Grade 10
Term nd2
20182017
تستخدم أوراق العمل للمساعدة على أداء األنشطة داخل الصف،
وال تغين عن الكتاب املدرسي
Covalent Bond
10th Grade
2nd Term, 2018
( 1 ) http://chemya.weebly.com/
Chemistry
Stability
All atoms are electrically neutral, because the number of positive protons forming the
nucleus is equal to the number of negative electrons rotating around the nucleus. In
repulsion, not all atoms are stable. Many atoms have high energy that makes them
unstable, forcing them to try to reach stability by reducing their energy. Chemical bonds
where the atom loses or acquires or shares valence electrons with other atoms.
Covalent bond: is the force of attraction that holds together two atoms that share a pair of
valence electrons.
Molecule: is the smallest particle of a covalent compound that still has the properties of the compound.
➢ As with ionic bonds, the electrons involved in covalent bond formation are those
occupy the last level of atoms (valence electrons)
➢ Covalent bonds often consist of non-metals.
➢ The covalent bond binds the atoms in diatomic molecules (H2, F2, O2, Cl2)
Why Covalent Bonds Form?
Covalent bonds form because they give atoms a more
stable arrangement of electrons. Look at the Oxygen
atoms in the Figure above. Alone, each Oxygen atom has
six valence electrons. By sharing two pairs of valence
electrons, each Oxygen atom has a total of eight valence
electrons. This fills its outer energy level, giving it the most
stable arrangement of electrons. The shared electrons are attracted to both Oxygen nuclei,
and this force of attraction holds the two atoms together in the Oxygen molecule.
Forces in molecules Fluorine atom (9F) has an electron configuration (1s22s22p5). Each Fluorine atom has seven
valence electrons and needs only one electron to reach the Octet. As the Fluorine
approaches each other, the electrical forces affect the state of the atoms.
The closer the two atoms are, the greater the attraction between the nucleus and the
electrons of the other atom until it reaches a point where the attraction forces between the
nuclei and electrons are greater than the repulsion forces between the nuclei, as well as
between the electrons in both atoms. Here the covalent bond is composed in the Fluorine
molecule (F2).
Attraction
The shared electrons are attracted to the nuclei of both atomsBetween The electrons
of both atoms
Between The nuclei
of both atoms
Repulsion
Forces
10th Grade
2nd Term, 2018
( 2 ) http://chemya.weebly.com/
Chemistry
By sharing one pair of electrons the two atoms reach an electron configuration similar to the
electron configuration of the nearest noble gas.
For each Fluorine atom, one pair of shared electrons (bonded electrons) and three not shred
pairs (unbonded electrons).
Numbers of bonds
Single covalent bonds
Sometimes atoms need a single electron to reach an electron configuration similar to noble
gas, with the participation of one pair of electrons. These atoms reach the stability state, as
in Fluorine in the previous example, or as Hydrogen Molecule H: H or H-H
The atom does not necessarily have to be associated with another atom of the same kind to
stabilizes, two different atoms can make a covalent bond by the participation of the electrons.
Single Bond
When only one paire of electrons is shared
When three paires of electrons is shared
When two paires of electrons is shared
Multible Covalent Bonds
Trible Bonds Double Bonds
Covalent Bonds
10th Grade
2nd Term, 2018
( 3 ) http://chemya.weebly.com/
Chemistry
Group 17 elements contain seven (7) valence electrons, they lack a single electron until
they reach stability. For example, the bond between Hydrogen and Fluorine is as follows,
H· + H ـــ
Group 16 elements, contain six (6) valence electrons, they need two electrons until the last
level complete with 8 electrons. Oxygen, for example, with electron configuration (1s22s22p4)
have two single covalent bonds with Hydrogen, one Oxygen atom shares a pair of electrons
with each Hydrogen atom to form a water molecule.
Group 15 elements, contain five (5) valence electrons, they need three electrons to reach
the last level complete with 8 electrons. Nitrogen , for example, its electron configuration
(1s22s22p3) have three single covalent bonds with Hydrogen, they share three pairs of
electrons, a pair with each Hydrogen atom to form the ammonia molecule.
Nitrogen can also combine with an element of group 17 such as Chlorine to form a Nitrogen
trichloride compound.
+
Group 14 elements, contain four (4) valence electrons, each one need four electrons until
it reaches the last level complete with 8 electrons. Carbon, for example, its electron
configuration (1s22s22p2) have four single bonds with atoms that share one pair of electrons,
it shares four pairs of electrons, a pair with each atom. For example, in a Chlorofluorocarbon
(CFC) used in refrigeration, the carbon atom is connected to four Chlorine and Fluorine
atoms,
· · · F :
· ·
· · F :
· ·
·
· N :
·
· ·
· Cl :
· ·
─ N :
· ·
: Cl :
│
· ·
: Cl
· ·
│
: Cl :
· ·
3
· · C ·
·
· · · Cl :
· ·
─ C
· · : Cl : │
· · : F
· · │
: Cl : · ·
· · · F :
· ·
· · ─ Cl :
· · 3 + +
10th Grade
2nd Term, 2018
( 4 ) http://chemya.weebly.com/
Chemistry
1) How does the covalent bond form?
_____________________________________________________________________________________________________________________
2) What is the smallest unit of the Covalent Compound formed by the chemical bonding of two or more atoms?
_____________________________________________________________________________________________________________________
3) Which types of elements used to form covalent bonds?
_____________________________________________________________________________________________________________________
4) What is the result of the participation of two atoms of the same element in valence electrons?
_____________________________________________________________________________________________________________________
5) Why do molecules consist of atoms rather than being atoms alone?
_____________________________________________________________________________________________________________________
6) What types of forces influence the components of atoms in molecules?
_____________________________________________________________________________________________________________________
7) Complete the following table,
Influential Forces
Suitable situation to form the bond
8) Draw the shape of the fluorine molecule
a) How many pairs of electrons are involved in each atom? ______________________________
b) How many pairs of unconnected atoms per atom? _______________________________________
9) What is the bond formed by the participation of one pair of electrons?
_____________________________________________________________________________________________________________________
10) Sketch Hydrogen molecule using Lewis structure.
10th Grade
2nd Term, 2018
( 5 ) http://chemya.weebly.com/
Chemistry
11) Complete the following tables.
Group 14 Group 15 Group 16 Group 17
# Valence electrons
# Electrons required for stability
# Electrons participate in the formation of the bond
# Created bonds
12) Draw the Lewis structure for
Cl2 HCl
13)
water H2O H2S
14)
NH3 phosphine PH3
15)
CH4 SiH4 CCl4
10th Grade
2nd Term, 2018
( 6 ) http://chemya.weebly.com/
Chemistry
Hybridization The electron configuration in the carbon atom is (1s22s22p2). As it is clear, the carbon atom
ends with a (p) sub-level containing only two electrons, it is easy to conclude that only these
two electrons are involved in the bond formation. But we have studied that carbon has four
bonds, and the reason is hybridization.
Electronic configuration of carbon atom
Hybridization between level 2s and 3p levels
produces four hybrid levels sp3
Hybridization: mixing sub-levels to form new hybrid levels
The number of hybrid levels produced is equal to the total number of levels entered in the
hybridization process. In the previous example, one orbital of 2s with three orbitals of 2p was
hybridized to produce four sp3 hybrid levels.
The sublevel (s) consists of a single orbital and sublevel (p) of three orbitals, making three
possibilities of hybridization, and the number of orbitals resulting from the hybridization is
equal to the total number of hybridized orbitals.
Orbitals overlapping The shapes of the orbitals in the sub-levels are varied. The sub-level (s) has a spherical
shape, while the three orbitals of the sub-level (p) are pear shaped in each of the three
directions.
s orbital p orbital
Hyberdization between s,p
Sp3 sp
* Form when the sub-
level (s) is mixed with
one sub-level (p) orbital.
* Produces two hybrid
orbitals with two non-
hybridized (p) orbitals.
* Form when the sub-
level (s) is mixed with
three sub-level (p)
orbitals.
* Produces four
hybrid orbitals.
* Form when sub-level
(s) is mixed with two
sub-level (p) orbitals.
* Produces three hybrid
orbitals with a non-
hybridized (p) orbitals.
Sp2
10th Grade
2nd Term, 2018
( 7 ) http://chemya.weebly.com/
Chemistry
Bonds are formed when orbitals overlap and there are two possibilities for such overlapping,
Multiple covalent bonds We have learned before that it is enough to some atoms to share one pair of electrons to
reach stability, such as bromine, while some atoms need to share more than one pair to be
stable like the elements in groups 14, 15 and 16 so the atoms of these elements make more
than one bond.
Double bonds
The Oxygen atom at the top of group 16 has 6 valence electrons, needs two electrons for a
noble-gas configuration. This is what happens when interacting with two Hydrogen atoms to
form a water molecule. But there is another way, by sharing two pairs of electrons with
another Oxygen atom. The two atoms are bound together by two bonds, one of them is
sigma (σ) and the other is pi (π).
Triple bonds
The elements in group 15, such as Nitrogen , have 5 valence electrons and need three
electrons for a noble-gas configuration, so they bonded by three pairs of electrons. The
Nitrogen atom can make three single bonds with other elements such as Hydrogen or a triple
bond with a similar Nitrogen atom.
Hed to hed (end to end) Side by side (parallel)
* The electronic density is low and
the bond is weak.
* The pi bond (π) is formed.
(s) with ( s)
(p) with ( p)
(s) with (p)
When hybrid levels
are involved in
association formation
* The electronic density is high and the
bond is strong.
* The sigma bond (σ) is formed
Orbitals overlaping
One σ bond, one π bond
One σ bond, two π bond
10th Grade
2nd Term, 2018
( 8 ) http://chemya.weebly.com/
Chemistry
Covalent bond strength
Remember that there are forces of attraction and repulsion between the electrons and nuclei
of the atoms that participate together to form a covalent bond. The molecule stabilizes when
the forces of attraction overcome the forces of repulsion. To break these forces we need
energy, the forces of attraction and repulsion vary in the compound, so the energy values
that are needed to break the covalent bond vary.
Bond length
Covalent bond length: the distance between the two the two bonded nuclei at the position of
maximum attraction.
The strength of the bond depends on the length of the bond. The length of the bond depends
on the strength of the attraction between the charges involved in the composition of the bond
and depends on the number of charges, the greater the number of charges the stronger the
attraction between them and thus the length of the bond decreases and its energy increase.
Molecule Bond type Bond length Bond-Dissociation Energy
F2 Single bond 1.43 × 10-10 m 159 kJ /mol
O2 Double bond 1.21 × 10-10 m 498 kJ /mol
N2 Trible bond 1.10 × 10-10 m 945 kJ /mol
It is clear from the table that trible bonds are shorter and have higher energy than double
bonds as well as double bonds are shorter than single bonds and higher energy.
Energy and bonds
It emits energy when forming bonds and in contrast we need energy to break those bonds.
Bond-Dissociation Energy: energy needed to break the covalent bond.
From the above table, it is clear that the bond dissociation energy depends on its type as
well as the length of the bond, the shorter the bond the greater energy needed to break.
The chemical reaction is simply defined as the breaking down bonds and forming new bonds.
As we have already said, breaking bonds requires energy. While the formation of bonds
produces energy, the reaction finally has energy equals to the difference between the energy
value we need to break the bonds and the energy that results from the bonds formation.
Endothermic Reaction Exothermic Reaction
When the energy emitted by the bonds
in the outputs is lower than the energy
needed to break the bond in the
reactants.
When the energy emitted by the bonds
in the outputs is greater than the
energy needed to break the bond in
the reactants.
The difference between the energy generated by the bonds formation and the energy needed to break the bonds
10th Grade
2nd Term, 2018
( 9 ) http://chemya.weebly.com/
Chemistry
16) Compare between the Sigma bond and the pi bond
Sigma bond σ pi bond π
How does it consist?
Bond energy
Number between two atoms
presence of electrons
17) What is the result when atoms share with more than one pair of electrons? _____________________________________________________________________________________________________________________
18) What is the result when atoms share with two pairs of electrons?
_____________________________________________________________________________________________________________________
19) Draw the Lewis structure of oxygen molecule O2
20) How many Sigma and Bi bonds are in the Oxygen molecule?
_____________________________________________________________________________________________________________________
21) What is the result when atoms share with three pairs of electrons?
_____________________________________________________________________________________________________________________
22) Draw the Lewis installation of the Nitrogen molecule N2
23) How many Sigma and Bi bonds are in the Nitrogen molecule? _____________________________________________________________________________________________________________________
24) How can I break the covalent bond? _____________________________________________________________________________________________________________________
25) Defined Covalent Bond Length. _____________________________________________________________________________________________________________________
26) Draw the Lewis structure for ethyne C2H2.
10th Grade
2nd Term, 2018
( 10 ) http://chemya.weebly.com/
Chemistry
27) What is the relationship between the length of the bond and the number of electrons involved?
_____________________________________________________________________________________________________________________
28) What is the relationship between the length of the bond and the strength of the bond?
_____________________________________________________________________________________________________________________
29) Draw a graphical curve between the length of the bond versus the energy of the bond and clarify the relationship between them.
_____________________________________________________________________________________________________________________
30) Defined Bond-Dissociation Energy. _____________________________________________________________________________________________________________________
31) What is the relationship between the length of the bond and the its dissociation energy? _____________________________________________________________________________________________________________________
32) What is the relationship between (bond formation / breaking) and (energy)? _____________________________________________________________________________________________________________________
What type of reaction when, 33) The energy generated by the bonds formation in products is greater than the energy needed to break the bonds in the reactors? _____________________________________________________________________________________________________________________
34) The energy produced by the bonds formation in products is less than the energy needed to break the bonds in the reactors? _____________________________________________________________________________________________________________________
35) Which of the following compounds has the shortest bond between its components? * H2 *O2 * Cl2 * N2
36) Select Sigma and Bay bonds in the following vehicles.
37) Define double Bond _____________________________________________________________________________________________________________________
10th Grade
2nd Term, 2018
( 11 ) http://chemya.weebly.com/
Chemistry
1) 38)which one of the Nitrogen -carbon bonds are shorter and weaker in the following compounds?
The table represents the bond energy values of some bonds between elements.
39) Predict the dissociation energy of covalent bonds for all that comes,
10th Grade
2nd Term, 2018
( 12 ) http://chemya.weebly.com/
Chemistry
Naming molecules Naming of binary molecular compounds
To name simple covalent compounds, follow these rules:
• Start with the name of the element closer to the left side of the periodic table.
• Follow this with the name of element closer to the right of the periodic table. Give this
second name the suffix –ide.
• Use prefixes to represent the numbers of the different atoms in each molecule of the
compound.
The binary molecular compounds consist only of two non-metals, such as P2O5, which is
used as a dehydrating substance.
5O2P
Di Phosphorus penta oxide Prefix #atoms Prefix #atoms
hexa 6 mono 1
hepta 7 di 2
octa 8 tri 3
nona 9 tetra 4
deca 10 penta 5
NameCompoundNameCompound
Nitrogen dioxideN2ONitrogen trifluoride NF3
Carbon dioxide CO2 Carbon tetrachloride CCl4
Common names Some compounds have common names and this is because they have been used for a long
time and have been given names by people even before they are chemically categorized,
such as,
Chemical name Common name
Hydrogen dioxidewaterH2ONitrogen dioxideNitrous OxideN2ONitride tri Hydride AmmoniaNH3
Di Nitrogen tetrahydride HydrazineN2H4 Nitrogen monoxide Nitric OxideNO
Prefix (penta)
Number of atoms
Oxygen
2nd non-metal
Prefix (di)
Number of atoms
Phosphorus
1st non-metal
10th Grade
2nd Term, 2018
( 13 ) http://chemya.weebly.com/
Chemistry
Naming acids Acid: The compound produces Hydrogen ions (H+) in solution, it is an acid.
When hydrochloric acid is placed in water it breaks down to H+ and Cl-
HCl H+ + Cl-
There are Two common types of acids exist binary acids and oxyacids.
naming binary acids Binary acids: An acid made up of Hydrogen and a non-metal.
Naming rules 1) We use the (Hydro) prefix at the beginning of the name.
2) followed by the name root of the non-metal followed by the suffix (ic)
3) We end with the conclusion (acid)
HCl
Hydrochloric acid
Naming Oxyacids Oxyacid: An acid that contains both a Hydrogen atom and an oxyanion.
Oxyanion ions: polyatomic ion containing one or more oxygen atoms.
Naming rules 1) We start with the name of the non-metal or its root.
2) We conclude with the suffix suitable for number of Oxygen atoms in Oxyanion that can be
deduced from the following table,
3) Second word is always (Acid)
OxyacidOxyanion
FormulaNameSectionSectionNameFormula
HClO hypochlorous acidhypo--ousHypo--itehypochlorite ClO-
HClO2Chlorous AcidousiteChloriteClO2-
HClO3Chloric acidicatechlorateClO3-
HClO4perchloric acidperr--ic perr--ate PerchlorateClO4-
** Some acids are multi-atoms but do not contain Oxygen, so we use the same rules that we
use with binary acids. Such as HCN, which is called hydrocyanic acid. Whose name is
derived from the cyanide ion (CN).
conclusion (acid)
suffix (ic)
Non-metal name root (Chlor)
Prefix (Hydro)
10th Grade
2nd Term, 2018
( 14 ) http://chemya.weebly.com/
Chemistry
Names and formulas for some famous acids
Name Formula Name Formula
Hydrobromic acid HBr Sulfurous acid H2SO3
Acetic acid HC2H3O2 (or HCH3COO, or HCH3CO2)
Chlorous acid HClO2 Chloric acid HClO3
Hydrochloric acid HCl Nitric acid HNO3
Phosphoric acid H3PO4 Carbonic acid H2CO3
Hydrofluoric acid HF Perchloric acid HClO4
Hypochlorous acid HClO Permanganic acid HMnO4
Sulfuric acid H2SO4 Boric acid H3BO3
Hydrocyanic acid HCN Nitrous acid HNO2
Hydroiodic acid HI Phosphorous acid H3PO3
40) Write the names for the following covalent compounds:
1. SiCl4 ___________________________________ 2. CO2 _______________________________________
3. SCl4 ___________________________________ 4. SiBr6 _______________________________________
5. NCl3 ___________________________________ 6. SeBr2 _______________________________________
7. P2O3 ___________________________________ 8. N2O5 _______________________________________
9. SCl6 ___________________________________ 10. OF2 _______________________________________
11. NF3 ___________________________________ 12. Si3N4 _______________________________________
13. SF4 ___________________________________ 14. CS2 _______________________________________
15. P2S5 ___________________________________ 16. As2O3 _______________________________________
17. PBr5 ___________________________________ 18. B2O3 _______________________________________
19. SeF6 ___________________________________ 20. NF4 _______________________________________
21. CO2 ___________________________________ 22. NO _______________________________________
23. SO2 ___________________________________ 24. SeO3 _______________________________________
25. NF3 ___________________________________ 26. SO3 _______________________________________
27. CCl4 ___________________________________ 28. N2O4 _______________________________________
29. P2O5 ___________________________________
10th Grade
2nd Term, 2018
( 15 ) http://chemya.weebly.com/
Chemistry
41) Write formulas for the following:
1. Tetraiodine nonoxide _______________ 2. tetraphosphorus decoxide _______________
3. DiNitrogen trioxide _______________ 4. Phosphorus triiodide _______________
5. Iodine heptafluoride _______________ 6. Diboron hexahydride _______________
7. Silicon tribromide _______________ 8. Iodine trichloride _______________
9. Phosphorus trihydride _______________ 10. Nitrogen tribromide _______________
11. Hexaboron silicide _______________ 12. DiNitrogen pentoxide _______________
13. Carbon monoxide _______________ 14. Sulfur hexachloride _______________
15. Carbon tetrachloride _______________ 16. Phosphorus trinitride _______________
17. Hydrogen monosulfide _______________ 18. Diphosphorus pentoxide _______________
19. Diboron tetrabromide _______________ 20. Disulfur decafluoride _______________
21. Sulfur trioxide _______________ 22. Boron trichloride _______________
23. Silicon dioxide _______________ 24. Hydrogen monoiodide _______________
25. Chlorine dioxide _______________ 26. tetraphosphorus
decoxide _______________
27. disulfur trioxide _______________ 28. diPhosphorus trioxide _______________
29. Nitrogen dioxide _______________ 30. Decafluoride disulpher _______________
31. trioxide diarsenic _______________ 32. Sulfur hexafluoride _______________
33. Hydrogen dioxide _______________ 34. Disulpher tetrafluoride _______________
35. Chlorine trifluoride _______________
10th Grade
2nd Term, 2018
( 16 ) http://chemya.weebly.com/
Chemistry
42) When The molecular compound can be named as an acid?
43) Complete the following table,
Name Oxyanion (if available)
Formula
HI
HClO3
HClO2
H2SO4
H2S
HNO3
HNO2
H2Se
H3PO4
Hydrobromic acid
Bromose acid
Iodic acid
Hydroflric acid
Chloric acid
Sulforic acid
Hydrochloric acid
10th Grade
2nd Term, 2018
( 17 ) http://chemya.weebly.com/
Chemistry
Molecular structures Structural formulas PH3 is a phosphine molecule. Its molecular formula shows that it consists of a phosphorus
atom and three Hydrogen atoms, but this formula does not explain how these four atoms are
bonded. To illustrate how these atoms bonded, one of the following methods can be used.
The previous models reflect the structural forms of the Phosphine compound.
Structural formula: The formula in which symbols and bonds are used to show the relative
positions of atoms.
Molecular formula: A formula that uses symbols and numbers to indicate the types and
numbers of elements involved in the composition of a molecule.
Lewis structures To draw Lewis structures for a specific molecule we follow the following steps,
Step 1: Identify the central atom:
✓ When the molecule contains more than one element, it is necessary to determine which
of these elements will be at the centre of the molecule. The atom of this element is the
lowest in the electronegativity and can be easly identified as it is always far from the
Fluorine element, which is the highest in the electronegativity.
✓ The corresponding table shows the
electronegativity values of a set of elements where
the number below the element is the value of the
electronegativity and shows that the carbon (2.55)
farthest from the Fluorine has a lower
electronegativity than the Nitrogen (3.04) closest
to Fluorine, which in turn has a lower
electronegativity than Oxygen (3.44) because
Oxygen is closer to Fluorine.
✓ Hydrogen is always a side atom.
10th Grade
2nd Term, 2018
( 18 ) http://chemya.weebly.com/
Chemistry
Step 2: Identify the bonds created:
1) Determine the number of electrons involved in the formation of bonds, which are, of
course, valence electrons, where we combine all the numbers of valence electrons for
all atoms involved.
2) Determine the number of bonds in the molecule, dividing the number from the previous
step by 2, where each bond is formed by the participation of two electrons (one in each
atom).
3) Put one bond between central atom and each subsidiary atom.
4) Select the number of bonds you've already set and compare them with the number of
bonds you've found in step (2).
5) Determine whether the central atom is bonded to binary or trigonal bonds with some
central atoms or one and draw double or triple bonds as appropriate for the central atom.
Carbon atoms, Oxygen, and Nitrogen are often multi-bonded, while Hydrogen atoms are
only single bonds.
Example,
Draw the Lewis structure for NH3
Step 1: Identify the central atom
The ammonia molecule consists of a Nitrogen atom and three Hydrogen atoms, and the
Nitrogen atom is the central atom.
Step 2: Identify the bonds created
1) Number of electrons involved,
The Nitrogen atom has 5 valence electrons and each Hydrogen atom has a single
equivalence electron.
(3 × 1) + 5 = 8 valence electrons
2) determine the number of bonds in the molecule,
(8 Valence electrons) / (2 electrons for each bond) = 4 bonds
3) Molecule drawing
We have a Nitrogen atom and three Hydrogen atoms
H─N─H│H
4) Calculate the remaining electrons
We have three 3 bonds with six 6 electrons and basically, we have 8 electrons,
leaving a pair of electrons and the final form will be,
. . H─N─H
│H
10th Grade
2nd Term, 2018
( 19 ) http://chemya.weebly.com/
Chemistry
Example Draw Lewis' structure for the CO2 molecule.
Step 1: Identify the central atom
The molecule consists of a carbon atom and two Oxygen atoms, so the carbon atom
is the central atom.
O C O
Step 2: Identify the bonds created
1) Number of electrons involved,
The Oxygen atom (in group 16) has six valence electrons,
The carbon atom (group 14) has four valence electrons,
(6 × 2) + 4 = 16 valence electrons
2) determine the number of bonds in the molecule,
(16 Valence electrons) / (2 electrons for each bond) = 8 bonds
3) Molecule drawing
O = C = O
4) Calculate the remaining electrons
We have three 4 bonds for eight electrons and basically, we have 16 sixteen
electrons, leaving four pairs of electrons and the final form will be,
. .. .O = C = O . . . .
10th Grade
2nd Term, 2018
( 20 ) http://chemya.weebly.com/
Chemistry
Example: Draw the Lewis structure of the ethylene molecule C2H4
Step 1: Identify the central atom
The compound consists of two Carbon atoms and four Hydrogen atoms, and the
carbon atoms are in the centre.
HH
CC
HH
Step 2: Identify the bonds created
1) Number of electrons involved,
The Hydrogen element atom (in group 1) has one equal electron,
The carbon element atom (group 14) has four valence electrons,
(4 × 2) + (1 × 4) = 12 valence electrons
2) determine the number of bonds in the molecule,
(12 Valence electrons) / (2 electrons for each bond) = 6 bonds
3) Molecule drawing
HH
C = C HH
4) Calculate the remaining electrons
We have 6 bonds in 12 twelve electrons and basically, we have twelve electrons 12
no pairs of electrons left and the final form will be,
HH
C = C HH
10th Grade
2nd Term, 2018
( 21 ) http://chemya.weebly.com/
Chemistry
Lewis structures for polyatomic ions The polyatomic ion is treated as a single-atom ion. The atoms are bonded by covalent bonds.
Because of ion charge, there is a difference in the numbers of valence electrons. In the
positive ions, the valence electrons are lower and, conversely, in the negative ion, the
number of valence electrons is higher.
Example: Draw Lewis structure of phosphate ion PO43-
Step 1: Identify the central atom
The molecule consists of a phosphorus atom and four Oxygen atoms, so the
phosphorus atom is the central atom.
O
OPO
O
Step 2: Identify the bonds created
1) Number of electrons involved,
The Oxygen atom (in group 16) has six valence electrons,
The phosphorus atom (group 15) has four valence electrons,
The ion charge (-3), so we add 3 three more electrons.
32 = (6 × 4) + 5 + 3 valence electrons,
(6 × 4) + 5 + 3 = 32 valence electrons
2) determine the number of bonds in the molecule,
(16 Valence electrons) / (2 electrons for each bond) = 8 bonds
3) Molecule drawing
O│
O ─ P ─ O │ O
4) Calculate the remaining electrons
We have four 4 bonds for eight electrons and basically, we have thirty two 32 electrons,
which leaves twenty-four electrons, or 12 pairs of electrons, and the final will be,
. . : O :
. . │ . .
O : ─ P ─ :O . .│
. .
: O :
. .
-3
10th Grade
2nd Term, 2018
( 22 ) http://chemya.weebly.com/
Chemistry
44) How many Hydrogen atoms in a molecule phosphine were observed phosphorous PH3? _____________________________________________________________________________________________________________________
45) highlight the ways of expression of phosphine were observed so that bearing the name of the way under the appropriate form. Structural formula * Ball and stick molecular model * Molecular formula * Lewis structure *
Space-filling molecular-model
figure
Expression
46) Fill in the following table for each atom
Atom Group # # Of Valence Electrons Electron Dot Notation # Of Possible Bonds
Ca
Se
Kr
C
Cs
Al
F
P
10th Grade
2nd Term, 2018
( 23 ) http://chemya.weebly.com/
Chemistry
47) Draw Lewis structure for the ammonia molecule NH3
48) Draw Lewis structure for BH3
49) Draw Lewis structure for carbon dioxide molecule CO2
10th Grade
2nd Term, 2018
( 24 ) http://chemya.weebly.com/
Chemistry
50) Draw Lewis structure for Phosphate ion PO43-
51) Draw Lewis structure for NH4+
52) Draw Lewis structure Lion ClO4-
10th Grade
2nd Term, 2018
( 25 ) http://chemya.weebly.com/
Chemistry
Resonance When attempting to draw a Lewis structure for NO3
-nitrate ion we find that there is a range
of possibilities
These possibilities are called resonance forms.
Resonance: A state occurs when there is more probability of drawing a Lewis structure for
the same molecule.
Note,
1) The location of electron pairs varies.
2) The presence of atoms does not change.
3) The bonds converted from single to double bonds and vice versa.
4) The molecule must contain different bonds, single and double.
5) Molecules that contain only single bonds have only one shape - no resonance -.
6) The molecule appears to have only one shape.
7) The lengths of the real bonds are equal to the average of the lengths of the bonds in
the resonance shapes.
Other examples for resonance situations,
O3Ozone
SO2Sulfur
dioxide
NO2-Nitrite
Ion
SO32-Sulfur
ion
10th Grade
2nd Term, 2018
( 26 ) http://chemya.weebly.com/
Chemistry
53) Define the resonance.
_____________________________________________________________________________________________________________________
Resonance Structures for a Carbonyl Group
54) How many total electrons are in structures I ( ) and II ( )?
55) Is the total number of electrons in each structure the same? (yes or no)
56) How many single bonds are in structures I ( ) and II ( )?
57) Is the number of single bonds the same in each structure? (yes or no)
58) How many lone pair electrons are in structures I ( ) and II ( )?
59) Is the number of lone pair electrons the same in each structure? (yes or no)
60) How many pi bonds are in structures I ( ) and II ( )?
61) Is the number of pi bonds the same in each structure? (yes or no)
62) Based on the answers above, describe what is different between structures I and II (in
terms of electrons)?
_____________________________________________________________________________________________________________________
63) Is the net charge of structure I the same as the net charge of structure II? (yes or no)
64) What do the curved arrows show in the above structure?
_____________________________________________________________________________________________________________________
65) draw resonance shapes for NO2-
66) draw resonance shapes for SO2
67) draw resonance shapes for O3
68) draw resonance shapes for SO32-
Normally atoms get eight valence electrons when bonded by a covalent bond, but some elements do not follow the Octet rule,
#VE: number of valence electrons
Exceptions to the Octet rule
Odd number of valence electrons Expanded octets
If we want to know how many
bonds are formed in a molecule, we
divide the total number of valence
electrons by 2, which means that
the number of valence electrons
should be an even number.
But some compounds have an odd
total number of valence electrons
and cannot be divided by 2.
#VE Lewis
structure Molecule
17NO2
19ClO2
11NO
Some elements, such as
phosphorus present in group 15,
contains 5 valence electrons, can
share five electrons in the formation
of covalent bonds as in the PCl5
phosphorus pentachloride.
The molecules in which the central
atom is connected to more than four
bonds have more than eight
electrons in its outer shell.
Some compounds reach stability by
less than eight electrons, which are
rare, including the element of boron,
which has three valence electrons
and stabilizes when it has three
bonds, it has only six electrons.
These compounds are reactable
because they can receive a pair of
electrons.
When an atom in a molecule received a pair of electrons from another atom, a bond is formed between two molecules called a Coordinate covalent bond.
Suboctets and coordinate
10th Grade
2nd Term, 2018 Chemistry
( 27 ) http://chemya.weebly.com/
69) Write three cases elements do not follow the Octet rule. _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________
70) complete the following table with the exception of the Octet rule.
Molecule
Exception
Molecule
Exception
71) What is the name of the phenomenon in the previous figure (between nitrogen, boron)? How composed? _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________
10th Grade
2nd Term, 2018 Chemistry
http://chemya.weebly.com/ ( 28 )
10th Grade
2nd Term, 2018
( 29 ) http://chemya.weebly.com/
Chemistry
Molecular shapes Most of the properties of the compounds depend on how their components are bonded and
on the shape of the molecule. Lewis structures can be used to identify the shape of the
molecule.
The shape of the molecule (molecular geometry) depends on.
1) The way the orbitals of different atoms overlap.
2) Number of shared electrons.
3) Number of unshared electrons (lone pairs).
VSEPR model
Valence Shell Electron Pair Repulsion (VSEPR). It depends on the formation of a shape in
a particular order that will reduce the repulsion to the lowest possible degree between the
pairs of shared and unshared electrons around the central atom.
Bond Angle
When connecting balloons together in different numbers it takes different shapes, these
shapes distinguished by the angles formed between balloons, we find these possibilities,
according to the number of balloons involved form the final.
Likewise, the pairs of electrons that exist around the atoms forming the molecule act as
balloons, forcing them to form certain shapes, separating the central atom from side atoms
by specific angles.
Bond Angle: angle between two lateral atoms and central atom.
The taste of the molecule is controlled by its shape. The taste receptors on the tongue
recognize the taste through the form of food particles. They can distinguish the tastes (salty,
acid, bitter, sweet, monosodium glutamate)
10th Grade
2nd Term, 2018
( 30 ) http://chemya.weebly.com/
Chemistry
When linking hybridization with the number of bonds formed we find that
Example# pi bonds# Sigma bondsHybridization
04sp3
13sp2
22sp
The type of hybridization in the compound can be deduced from the number of bonds formed.
For example, in an aluminium chloride compound in which three Chlorine atoms branching
from the central Aluminium atom by three sigma bonds, which resembles a sp2 hybridization.
We always consider the pair of unconnected electrons to be a sigma bond. For example, in
water molecule, consisting of a central oxygen atom and two hydrogen atoms, there are two
Sigma bonds between oxygen and hydrogen with a couple of unshared electrons. That
oxygen is surrounded by four Sigma bonds, so, hybridization in water molecule is sp3.
10th Grade
2nd Term, 2018
( 31 ) http://chemya.weebly.com/
Chemistry
Each molecule has its own shape, which depends on the number of shared and unshared
electron pairs as well as on the elements that are associated with the central atom.
10th Grade
2nd Term, 2018
( 32 ) http://chemya.weebly.com/
Chemistry
72) Write three variables affecting the shape of the molecule. _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________
73) What is the name of the model used to express the shapes of particles? what it based on?
_____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________
74) Identify the bond angle.
_____________________________________________________________________________________________________________________
75) What types of taste, which distinguished by the tongue?
_____________________________________________________________________________________________________________________
76) Complete the following table
Examble# π bonds# σ bondsHyberdization
sp3
sp2
sp
77) What is the maximum number of hybrid orbitals could the Carbon atom form? _____________________________________________________________________________________________________________________
78) What is the molecular form for each of the following? (consider that there is no unshared electrons)
Shape Molecule
10th Grade
2nd Term, 2018
( 33 ) http://chemya.weebly.com/
Chemistry
79) Complete the following table
Molecular
geometry Hybridization
#
unshared
pairs
#
shared
pairs
#
Electron
pairs
Lewis st. Molecule
BeCl2
AlCl3
CH4
PH3
H2O
80) Whenever the hydrazine molecule (PH3) has the same structure of Aluminum chloride (AlCl3) molecule, consists of a central atom and three terminal atoms but it has a different form, why? _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________
81) The bond angle in the water molecule is not 180o, while, water molecule consists of a central atom and two terminal atoms, why? _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________
10th Grade
2nd Term, 2018
( 34 ) http://chemya.weebly.com/
Chemistry
Electronegativity and polarity
Basic Information About Electronegativity ➢ Fluorine has the highest Electronegativity 3.98 while francium has the lowest 0.7
➢ Most tables do not include values for noble gases because they are often not involved
in reactions.
➢ In the case of an inert gas included in a compound its Electronegativity will be very
high, close to halogens values.
➢ Lanthanides and actinides range from 1.12 to 1.7
➢ As the Electronegativity increases, the atom attraction to the bond electrons increases,
the electrons in the bond are close to the higher Electronegativity atom.
The atoms of the same type attract electrons from both sides equally,
the electrons are present in approximately equal proportions.
The different atoms attract the electrons with different forces, where the electrons are closer to the higher
Electronegativity atom.
Electron affinity Electronegativity
measure of the tendency of an atom to accept an electron
The relative ability of an atom to attract
electrons in a chemical bond Excluding noble gases, it increases with
increasing atomic number within a period.
Decreases with increasing atomic number within a group
Decreases with increasing atomic number within a group
Values were measured Values were assigned
Increases with increasing atomic number within a period.
Electronegativity and Electron affinity
Bond character The bond type depends on the attraction force of the atoms to the bond electrons.
We use the Electronegativity difference between the atoms involved in the formation of the bond to determine the type of bond
between them,
bond typeElectronegativity
difference
Non-polar covalent
(pure covalent) 0
Often covalent Less than 0.4
Polar covalent Between 0.4 and 1.7
Often ionic Greater than 1.7
Affect by the electric field
Location of the bond electronsBond typeThe ratio of
the ionicDifference in the Electronegativity
Types of atoms
Not affectedElectrons evenly distributed
between atoms (H2)pure covalent (non-
polar covalent)ZeroZero
Two atoms of the same type
Not affectedIn the middle of the distance but slightly near the higher
Electronegativity atomcovalent non-polar Between zero
and 5%Between zero
and 0.4
Atoms of different types Affected Near the higher
Electronegativity atom (HI)Covalent
Between 5% and 50%
Between 0.4 and 1.7
Affected Electron moves to the higher atom (NaCl)
IonicGreater than
50%Larger than 1.7
10th Grade
2nd Term, 2018 Chemistry
( 35 ) http://chemya.weebly.com/
Polarity The electrodes (+ve or -ve) are made up of any material when the charges on the material
differ. For example, the battery carries a positive charge on one end and a negative charge
on the other end and we call it the battery poles.
By the same way, the molecule is polar, ie, has electrodes when one of the ends carries a
positive charge and the other carries a negative charge. When the molecule is from the same
element atoms, the electrons rotate around it in the same way and spend similar times
around the atoms, making them neutral all the time. They do not have poles. Therefore, we
call the bond (non-polar)
Polar Covalent bonds The polar covalent bond is formed when the Electronegativity difference between the atoms
forming the bond is greater than 0.4. The force of attracting bonding electrons by one atom
is larger than the other atom. The electrons spend much longer time around the higher atom
in the Electronegativity making it carry a partial negative charge symbolized by the symbol
(δ-), The other atom carries a positive molecular charge (δ+).
Dipole: The polar bond resulting from the formation of partial charges on atoms forming a
covalent molecule.
Polarity and molecular form The polarity sometimes depends on the shape of the molecule. When comparing the water
molecule (H2O) and the carbon tetrachloride (CCl4) molecule, we find the following,
Carbon tetrachloride (CCl4) Water (H2O)
0.611.24Electronegativity difference
polarpolarBonds Polarity
non-polarpolarMolecule polarity
Geometry
The symmetry (regular shape) of
CCl4 molecule (tetrahedron)
makes equal distribution of the
charges, making the molecule as a
whole acting as neutral, without
molecular charges.
The irregular shape of the water
molecule (bent) makes unequal
distribution of the charges,
forming poles carrying positive
and negative molecular charges.
Interpretation
10th Grade
2nd Term, 2018 Chemistry
http://chemya.weebly.com/ ( 36 )
10th Grade
2nd Term, 2018
( 37 ) http://chemya.weebly.com/
Chemistry
Solubility of polar molecules
Solubility: The ability of a substance to dissolve in another substance.
What determines the solubility of a molecule?
1) Type of bonding.
2) Shape of the molecule.
The polar and ionic molecules dissolve in water, on the other hand, the
non-polar substances dissolve in non-polar solvents.
properties of covalent compounds The bond between atoms in the molecule is strong, but the intermolecular forces between
the different molecules is rather weak, unlike the bond between ions in ionic compounds,
which is stronger because they are between all the ions of substance in the crystal.
The forces that bind the molecules Van der Waals forces: weak attraction forces between molecules.
Van der Waals forces
Hydrogen bond Dipole-dipole force Dispersion force
It consists of a hydrogen atom at a
dipole of a molecule and an atom
(oxygen, nitrogen or fluorine) at a
dipole of a nearby molecule.
the forces that bind
different partially charged
ends in neighbouring
molecules
A force that binds non-
polar molecules
Stronger than dipole-dipole force Stronger (but still weak) Very weak
Forces and properties Because the forces between molecules in covalent compounds are weak, their melting and
boiling points are low compared to ionic compounds. That is why sugar melt faster than salt
and too many molecular compounds (covalent) in room temperature are in the gaseous
state, such as carbon dioxide (CO2).
Even covalent solid compounds are as soft as paraffin wax, and solids come in a grid similar
to the crystalline network of ionic compounds, but of course they are weaker.
Covalent Network Solids
Covalent Network Solids: substances whose components are
connected by a network of covalent bonds.
They are often brittle and not connecting heat or electricity, but they
are very tough, such as diamonds in which each carbon atom is
attached to four other carbon atoms in a grid, so it forms a strong
crystalline arrangement which has a high melting point.
10th Grade
2nd Term, 2018
( 38 ) http://chemya.weebly.com/
Chemistry
82) Compare between Electronegativity and Electron affinity
Electron affinityElectronegativity
Definition
Trend cross group
Trend cross period
How to calculate the value?
83) What is the highest element in the value of Electronegativity? _____________________________________________________________________________________________________________________
84) Electronegativity values for noble gases do not written in some tables, why? _____________________________________________________________________________________________________________________
85) How much the electronegativity value for inert gases when involved in compounds? _____________________________________________________________________________________________________________________
86) To which in the molecule, electrons will be close? _____________________________________________________________________________________________________________________
87) Examine the pictures then answer
Describe the percent of electrons presence around the atoms.
compare Electronegativity in both
cases
Explain the similarity of the atoms in the
molecule, are similar or different?
10th Grade
2nd Term, 2018
( 39 ) http://chemya.weebly.com/
Chemistry
88) complete the following table
bond typeElectronegativity difference
0
Less than 0.4
Between 0.4 and 1.7
Greater than 1.7
Use this graph to answer following questions 89) Molecule A has (0) difference in the Electronegativity between the components. describe it. _____________________________________________________________________________________________________________________
90) classify the following molecules, HI: _________________________________________________________________________________________________________________
LiF: ________________________________________________________________________________________________________________
91) What does the symbol (δ) refer to? _____________________________________________________________________________________________________________________
92) defined the Dipolar force. _____________________________________________________________________________________________________________________
Per
cen
t io
nic
ch
ara
cter
75%
50%
25%
3.0 2.0 1.0
Electronegativity difference
LiF
LiI
CaO
HI
HF
CsCl
0.4 1.7 A
10th Grade
2nd Term, 2018
( 40 ) http://chemya.weebly.com/
Chemistry
93) Compare between Ammonia molecule (NH3) and Boron trifluoride molecule (BF3).
Boron trifluoride (BF3). Ammonia (NH3)
21.46Electronegativity difference
Bonds Polarity
Molecule polarity
Geometry
Interpretation
94) What determines the solubility of a molecule? _____________________________________________________________________________________________________________________
95) point to the negative atom in the following
C-N C-O C-S C-H 96) in any substance do the polar compound dissolved? _____________________________________________________________________________________________________________________
97) in any substance do the nonpolar compound dissolved? _____________________________________________________________________________________________________________________
98) Compare the forces between the components in a crystalline ionic compound and in a Covalent Network Solids. _____________________________________________________________________________________________________________________
_____________________________________________________________________________________________________________________
10th Grade
2nd Term, 2018
( 41 ) http://chemya.weebly.com/
Chemistry
99) What are the forces that bind the molecule components? Describe its strength. _____________________________________________________________________________________________________________________
100) Compare Van der Waals different forces.
Van der Waals forces
101) Sugar melts faster than salt, why? _____________________________________________________________________________________________________________________
102) What are the Covalent Network Solids? _____________________________________________________________________________________________________________________
_____________________________________________________________________________________________________________________
_____________________________________________________________________________________________________________________
103) Write under each of the following if it is polar or nonpolar
10th Grade
2nd Term, 2018
( 42 ) http://chemya.weebly.com/
Chemistry
104) List all types of intermolecular forces that would occur in each of the following,
a. CH3CF3 ______________________________________________________
b. CCl4 ______________________________________________________
c. SO2 ______________________________________________________
d. BrF ______________________________________________________
e. (CH3)3N ______________________________________________________
f. PCl5 ______________________________________________________
105) Circle all of the species below that can form a hydrogen bond in its pure form. Explain why the other species couldn't hydrogen bond.
C2H6 CH3NH2 KCl CH3CH2CH2OH CH3OCH3
_____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________
_____________________________________________________________________________________________________________________
106) Rank the following compounds from weakest intermolecular forces to strongest. Justify your answers.
H2S I2 N2 H2O _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________
107) Rank the following from weakest intermolecular forces to strongest. Justify your answers.
H2Se H2S H2Po H2Te _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________
_____________________________________________________________________________________________________________________