how many valence electrons do atoms want to obtain?
TRANSCRIPT
Find the correct formula for a compound!!•Use the oxidation #’s•Put the positive one first
H+1 + O-
2 H2O
Remember: A bond between a metal and a non-metal atom The metal keeps its name, and the non-metal ends in -ide
KBr
CaCl2
Potassium BromideCalcium Chloride
HON – 17
As pure elements, these seven elements form molecules containing two atoms
H2
N2 O2 F2
Cl2Br2
I2
HON – 17
As pure elements, these seven elements form molecules containing two atoms
Transition Elements
Atoms combine to form compoundsBy bonding atoms together, their properties change
I. Bonding
A.Chemical Bond
This is the attractive force between atoms or ions
Results from the rearrangement of valence electrons
B. Energy Changes
As a chemical bond forms, atoms are brought to a lower energy state
Free atoms have more energy than bonded atoms
H2O2H2O
EXOTHERMIC
As we said before, atoms can bond together by moving their valence electrons around
Actually, atoms can either lose, gain or share electrons. This gives us several types of bonds
Ionic Bond
BONDS BETWEEN ATOMSAtoms transfer electrons
Creates ions
Forming ions An ion is formed when atoms lose or gain electrons
Ion = Charged atom due to a loss or gain of electrons
e-e-e-e-e--+
Binary Ionic Compounds
- change the end of the non-metal to -ide
MgI2 Magnesium Iodide
CoBr2 K2O
CoBr3
Potassium Oxide
Cobalt (II) Bromide
Cobalt (III) Bromide
When you have more than two elements, refer to Ref. Table E.
NaOH Sodium HydroxideAmmonium NitritePotassium
PermanganateKMnO4
(NH4)(NO2)
Ni2(CrO4)3 Nickel (II) chromate
You must look at the types of atoms and their electronegativity differences.
Ionic - bond between a metal and a non-metal Electronegativity difference should be = to or > than 2.0 This means that one atom can pull an e- from another
atom
Results in the formation of ions
Mn + F
1.6 - 4.0 = 2.4
K + O 0.8 - 3.4 = 2.6
Big Dog vs Little Dog
Metal + nonmetal Ionic bond
• Further apart on the Periodic table
Higher ionic character• Greater difference in
electronegativity
High ionic character
Higher ionic character
=
You must look at the types of atoms and their electronegativity differences.
Covalent -
bond between two non-metals Electronegativity difference should be less than 2.0
This means that one atom is not able to pull an e- away
DOES NOT FORM IONS!!!
Two of the same sized dogs
C
+
Cl 2.6 - 3.2 = 0.6
I +
I 2.7 - 2.7 = 0.0
Covalent -
bond between two non-metals Specific Types
Polar Covalent Electronegativity differences of 0.5 – 1.9
- the unequal sharing of e-
Fe2O3 1.8 - 3.4 = 1.6
Results in partial charges on the atom
Non-Polar Covalent
- the equal sharing of e-
Electronegativity differences of 0.0 – 0.4
Usually only in diatomic molecules O2 3.4 - 3.4 = 0.0
Nonmetal + nonmetal• Covalent bond• Small difference
in electronegativity
Ternary substance- compound containing polyatomic ion
Polyatomic ion is covalently bonded together
Bond between polyatomic ion and atom is ionic
MgSO4
covalent
Ionic
Results in a compound having both IONIC and COVALENT bonds
Metal + Metal Metallic bond
Alloy -Different metal atoms mixed together
Brass –
= sea of electronsElectrons are free to move all over, not bound to one nucleus
Bronze – copper and tin
copper and zinc
Gold – Gold, silver, copper
Ionic compounds can also be drawn as Lewis structures.
Positive ion Cation
Since all the valence electrons are removed, no valence electrons are shown.
Na
Negative ion Anion
The charge is written above+
The added valence electrons indicate a full valence shell.
Cl
Brackets are added and the charge is written on the outside
-
LEWIS STRUCTURES OF IONS AND IONIC COMPOUNDS
Covalent compounds
First write element symbols and then draw their valance electrons.
H2
OH H O
Now move the atoms to pair up any unpaired electrons
HHO
CO2
Give the formula and dot diagram for the compound formed from the following compound:
EN difference ?
Fluorine and Magnesium
Give the formula and dot diagram for the compound formed from the following
elements:
EN difference ?
Strontium and Bromine
Give the formula and dot diagram for the compound formed from the following
elements:
EN difference ?
NH3
Give the formula and dot diagram for the compound formed from the following
elements:
EN difference ?
Give the formula and dot diagram for the compound formed from the following
elements.
Phosphorus and Chlorine
Pδ-
δ-
δ-
δ+
Cl
Cl
Cl
Cl
Cl
Cl
What are they? • The attractive force between the hydrogen attached to a highly electronegative atom of one molecule and a highly electronegative atom (N, O, F only) of a different molecule.
• Only found in polar covalent compounds
• Individually a very weak bond
•Very High M.P. and B.P.
•Less dense as a solid
•High Heat of Vaporization• Sweating, climate moderation
•High Surface Tension
Unique properties of water
Fewer molecules to be attracted to therefore a stronger attraction
Hydrogen bonding is the strongest of the intermolecular bonds!!!!
(click for video)
Strontium and Iodine
Give the formula and dot diagram for the compound formed from the following
elements:
Sr II
-1
-1
+2
BUBBLES
The Jesus lizard – the Basilisk lizard
scroll down to view movie
Rules are similar to ionic compounds, just need to add prefixes for the number of
atoms1
2
3
4
5
6
7
8
9
10
mono-di-
tri-
tetra-
penta-
hexa-
hepta-octa-
nona-
deca-
Try the following:
CO2
CCl4
Dinitrogen monoxide
Diphosphorus pentoxide
Carbon dioxide
Carbon tetrachloride
N2O
P2O5
A. State evidence that indicates that NH3 has stronger intermolecular forces of attraction than CF4.
B. Draw the lewis dot diagram for CF4. Is it a polar or non-polar molecule
Physical Properties of CF4 and NH3 at STP
Compound MP (ºC) BP (ºC) Solubility in water @ 20ºC
CF4 -183.6 -127.8 Insoluble
NH3 -77.7 -33.3 Soluble
Molecules -are only covalently bonded
Polarity of molecules - - completely dependent on the shape of the molecule
A molecule is either polar or non-polar with respect to charge
- molecules are only polar if they have polar covalent bonds
- if you can draw one straight line and all the (+) are on one side and all the (-) are on the other side, the molecule is polar
DipoleMolecule which has a + side and a - side
Assigning + and - to atoms
The atom with the higher electronegativity gets the -The atom with the lower electronegativity gets the +
Examples
O == C== O H--Cl
N
H H H- + -
nonpolar
+ -
polar
-
+ + +polar
Symmetrical charge distributionEqual distribution of charge
- results in the formation of a Nonpolar molecule
Asymmetrical charge distributionNegative(-) end and Positive(+) end
- results in the formation of a Polar molecule
A substance containing free ions that makes the substance electrically conductive
The process where ionic compounds split (separate) into their respective ions
Draw the Dot Diagrams for the following compounds and
determine if they are polar or non-polar, and name them:
H2O
CH4
Connectors # Needed Spheres # Needed
Sticks 6
Black 2
Red2
Springs 4 Yellow 4
You might have to share with another group to get 4.
Green 1
Blue 1
III. VSEPRClass Shape Model Example
AX Linear HCl
AX2 Linear CO2
AX3Trigonal Planar
BH3
AX4 Tetrahedral CH4
: AX3 Pyramidal NH3
..
:AX2BENT H2O
A substance will conduct electricity IF it has freely moving charged particles Particles can be ions, electrons, etc. as long as they can move
Metal Conducts electricity in solid or liquid form
Freely moving electrons allows the electricity to flow.
Ionic substanceDoes NOT conduct in solid formIons are locked in placeHas charges, but not free movingLiquid When melted, can conduct electricityIons are mobile enough to move past each other
-+
--
---
+
+
++
+
SolutionIn solution, ions separate
Ions are free to move, conducts electricity
Dissociate
Covalent
Solid Doesn’t conduct electricity No charged particles
LiquidDoesn’t conduct electricity No charged particles
Solution Some types of covalent molecules can be broken down to make ions Ionization
Conducts some electricity, because only a few of the molecules in the sample are broken down
Used to determine a substances properties – only found in covalently bonded substances
Relatively weak compared to ionic, metallic, and even covalent bondsExamples
Dispersion forces – for your college educationDipole-Dipole forces – again something for collegeHydrogen bonding – we’ve done theseMolecule-ion attractions – we’ll look at these
FORCES BETWEEN MOLECULES(IMF)’S
Molecule-Ion Attractions – the attraction between the ions and molecules of water in a solution
A Good Animation
Ionic•Hard
•Good Conductors• Not as solids
•High MP & BP
•Dissolve in Polar Substances - water
Covalent•Generally soft
•Poor Conductors• No charged particles
•Low MP & BP
AKA – Molecular Substances
Coordinate Covalent Bond
Hydronium ion
Ammonium ion
- one atom donates BOTH electrons that are shared
OH
H
+ H+
HOH H
+
NHH
+ H+
H NH
H
HH +
Give the name of a substance that can NOT conduct
electricity in the solid phase but can as a liquid. Explain
why.
Covalent bonds are classified as single,
double,
or triple bonds depending on the number of electrons shared between the two nuclei.
Intermolecular Forces
11.2
Intermolecular forces are attractive forces between molecules.
Intramolecular forces hold atoms together in a molecule.
Intermolecular vs Intramolecular
• 41 kJ to vaporize 1 mole of water (inter)
• 930 kJ to break all O-H bonds in 1 mole of water (intra)
Generally, intermolecular forces are much weaker than intramolecular forces.
“Measure” of intermolecular force
boiling point
melting point
DHvap
DHfus
DHsub
Types of Intermolecular Forces
3. Dipole-Dipole Forces
Attractive forces between polar molecules
Orientation of Polar Molecules in a Solid
11.2
Sodium Atom Chlorine Atom
+11 -11
Total charge
Atom is considered
Total charge
Atom is considered
+17 -17
0
neutral
0
neutral
IN AN IONIC BOND, ONE ELECTRON FROM SODIUM IS TRANSFERRED TO CHLORINE
-10
+1
a positive ion
-18
Called a Cation
-1 a negative ion
Called an Anion
CationAnion
Positive ion due to the loss of electronsNegative ion due to the gain of electrons
meow.
Examples - Determine the type of ion shown and explain how it was made from a neutral atom.
Ion Type of Ion How it was made
K+
Ca+2
O-2
Br-
cation Lost 1 electron
cation
anion
anion
Lost 2 electrons
Gained 2 electrons
Gained 1 electron
Draw the electron dot formula for neutral atoms of Na and F
Na F
All atoms want a full octet in their valence shell. This is a stable configuration. When ionic bonding occurs,the one valence electron in Na is transferred to F
+ -
Notice how both atoms have a full octet?F has gained an electron to get a total of 8.
Na uses its full shell underneath as a full valence
Na2
8 1
+
The attraction between the + and - ion causes the bond
Review Ionic bonds
1. Electrons are transferred2. Ions are created Cation lost e-, anion gained e-3. Very strong bond. Has high melting and boiling points, and a very rigid structure4. Creates ionic substances
Covalent Bondsa. Electrons in bonds
- No transfer of electrons- Electrons are shared between valence shell of atoms
- Weaker bonds than ionic
In covalent bonding, atoms get a full octet by sharing
electrons between their valence shells
Hydrogen and helium do not need 8 electrons, only 2
H HSo the molecule H2 looks likeH H
In covalent bonding, atoms still want to achieve a noble gas configuration
But rather than losing or gaining electrons, atoms now share an electron pair.
The shared electron pair
is called a bonding pair
COVALENT BONDS
The octet rule
Look at the parts of H2O
H H O O
H
H
This indicates that H2O looks likeH---O | H
Not H--O--H
Or H--H--O
Review
In a covalent bond, electrons are shared between valence shellsThere is NO transfer of electrons, so no ions are formedTheir bonds are weaker, have lower melting and boiling points
If atoms are covalently bonded, they make