Chemical BondingChemical Bonding

Chemical Bonding is the mutual electrical Chemical Bonding is the mutual electrical attraction between the nuclei and valence attraction between the nuclei and valence electrons of different atoms that binds the electrons of different atoms that binds the atoms together.atoms together.

chemical formulachemical formula..

The composition of a formula is given by The composition of a formula is given by its its chemical formulachemical formula..

A chemical formula indicates the relative A chemical formula indicates the relative number of atoms combined using atomic number of atoms combined using atomic symbols and numeric subscriptssymbols and numeric subscripts

HH22O, CO, C66HH1212OO88, FeCl, FeCl33, CaS, Li, CaS, Li33PP

Diatomic moleculesDiatomic molecules

Di = twoDi = twoAtomic = atomsAtomic = atoms

two atomstwo atomsDiatomic molecules contain only two Diatomic molecules contain only two atoms.atoms.

FF22

HH2 2

NaCl NaCl

Learn the following diatomic Learn the following diatomic elementselements

FF22

ClCl22BrBr22

II22

AtAt22

HH22

OO22

NN22

HalHONHalHONAll the hologens plus Hydrogen, Oxygen and Nitrogen All the hologens plus Hydrogen, Oxygen and Nitrogen

Lewis StructuresLewis Structures

Lewis Structures only show the valence Lewis Structures only show the valence electrons. electrons.

Write the element symbol Write the element symbol

CC

Lewis StructuresLewis Structures

Place one dot to the right of the symbolPlace one dot to the right of the symbol

C C

Lewis StructuresLewis Structures

Then add the next electron below the Then add the next electron below the symbolsymbol

C C

Lewis StructuresLewis Structures

The next electron goes to the leftThe next electron goes to the left

C C

Lewis StructuresLewis Structures

Continue moving around the symbol until all Continue moving around the symbol until all electrons have been added.electrons have been added.

N N

Lewis StructuresLewis Structures

Using electron dot diagrams, a diatomic Using electron dot diagrams, a diatomic molecule of hydrogen can be molecule of hydrogen can be represented asrepresented as

HH

B period ¼

H

Write the Lewis Structures for the Write the Lewis Structures for the following elementsfollowing elements

Li Li BeBe B B CC

NN OO F F NeNe

Lewis Structures are useful in seeing Lewis Structures are useful in seeing where an atom is willing to make a bondwhere an atom is willing to make a bond

Atoms can not bond when electrons are Atoms can not bond when electrons are pairedpaired

Helium has full shell with two electrons So Helium has full shell with two electrons So it is writtenit is written

HeHe: :

N has N has 55 valence electrons valence electrons

NN: :

It can only bond in three spots It can only bond in three spots

Chemical BondingChemical Bonding

There are several types of bonds –There are several types of bonds –

IonicIonic

CovalentCovalent

MetallicMetallic

Covalent bondsCovalent bonds

Covalent bondsCovalent bonds are when nonmetallic are when nonmetallic elements share an electron pair.elements share an electron pair.

Nm Nm + Nm + Nm

This can be two hydrogen atoms, HThis can be two hydrogen atoms, H22 or or

many different elements such as in many different elements such as in sucrose (Csucrose (C66HH1212OO66))

Molecular compoundMolecular compound

Molecular compoundMolecular compound is the simplest unit is the simplest unit for molecules.for molecules.

Remember that only the valance electron Remember that only the valance electron are involved in bonding.are involved in bonding.

A molecule is a A molecule is a neutralneutral group of atoms group of atoms that are held together by covalent bonds.that are held together by covalent bonds.

Atoms Atoms shareshare electrons electrons

Covalent bondsCovalent bonds

are when nonmetallic elements share an electron pair.are when nonmetallic elements share an electron pair.Nm Nm + Nm+ Nm

  1s1s 2s2s 2p 2p

F F . . F F . .

  F F F F F F F F

  This is the octet rule for covalent bonding.This is the octet rule for covalent bonding.

There are several types of covalent bonds. There are several types of covalent bonds.

PolarPolar

NonpolarNonpolar

Coordinate Coordinate

They tell how well elements share electrons They tell how well elements share electrons

Polar CovalentPolar Covalent

is a covalent bond that does not share the is a covalent bond that does not share the electrons equally. electrons equally.

One side is slightly + and the other is One side is slightly + and the other is slightly –slightly –

Because there are two poles of charge Because there are two poles of charge involve, the bond is a involve, the bond is a dipole.dipole.

H OH O

A dipole caused by the polar covalent bond

of the water molecule

Nonpolar CovalentNonpolar Covalent

is a covalent bond where the electrons are is a covalent bond where the electrons are evenly shared.evenly shared.

F FF F

Electronegativity!Electronegativity!

So how do we know what type of bond we So how do we know what type of bond we have?have?

Electronegativity! Electronegativity!

Covalent Covalent

Nonpolar Nonpolar Polar Ionic Polar Ionic

E 0-0.3E 0-0.3 0.3-1.7 1.7-3.3% 0.3-1.7 1.7-3.3%

Use the electronegative difference to Use the electronegative difference to determine the bond type. The determine the bond type. The electronegativity can be found on the electronegativity can be found on the periodic tableperiodic table

Sulfur and Hydrogen Sulfur and Hydrogen

Sulfur’s electronegativity is 2.5Sulfur’s electronegativity is 2.5

Hydrogen’s electronegativity is 2.1Hydrogen’s electronegativity is 2.1

S – H = S – H = 2.5-2.1 = 0.42.5-2.1 = 0.4

Where does it fall?Where does it fall? Polar covalent

Which element is least negative?Which element is least negative?

HH

So it is written first in the formulaSo it is written first in the formula

Try some moreTry some more

FF22 or F – F, SF or F – F, SF44, LiF, LiF

CompoundCompound FF22 SFSF44 LiFLiF

Electronegativity Electronegativity DifferenceDifference

Type of BondType of Bond

The HF (Hydrofluoric) can be written:The HF (Hydrofluoric) can be written:

+ + --H – F HH – F HFF

The 'The '+' and '+' and '-' symbols indicate partial -' symbols indicate partial positive and negative charges. positive and negative charges.

Coordinate covalentCoordinate covalent

bond is a bond formed when one atom bond is a bond formed when one atom provides both electrons in a shared pair.provides both electrons in a shared pair.

HH NN HH

HH

How do we know if a double or How do we know if a double or triple bond in needed?triple bond in needed?

Using the equations to correctly draw the Using the equations to correctly draw the Lewis Structure and Structural Formula for Lewis Structure and Structural Formula for each of the following.each of the following.

All Single BondsAll Single Bonds6(N) + 2 = VE6(N) + 2 = VE

N= number of atoms (not counting H)N= number of atoms (not counting H)

VE = # of valence electronsVE = # of valence electrons

p+

e-

p+

e-

No interaction between atoms

p+

e-

p+

e-

Attraction begins

Covalent bond forms

p+ p+

e-

e-

Network SolidsNetwork Solids

"Covalent Crystals" (crystal is used to "Covalent Crystals" (crystal is used to describe Ionic structures) (Diamonds) describe Ionic structures) (Diamonds) – Hard Hard – Good insulators Good insulators – Transparent Transparent – High Melting Point High Melting Point

Properties of Covalent Properties of Covalent CompoundsCompounds

These are poor conductors of electricity in These are poor conductors of electricity in the fused or dissolved state the fused or dissolved state

Nonelectrolytes-do not conduct electricity Nonelectrolytes-do not conduct electricity in water in water

Poor conductors of heat and electricity Poor conductors of heat and electricity

Brittle or cleave rather than deform Brittle or cleave rather than deform

Covalent CompoundsCovalent Compounds

Exist as neutral molecules (CExist as neutral molecules (C66HH1212OO22))

Solids, liquids, or gases (CSolids, liquids, or gases (C66HH1212OO22(s), (s),

HH22O(l), COO(l), CO22(g))(g))

Lower melting and boiling points (i.e., Lower melting and boiling points (i.e., often exist as a liquid or gas at room often exist as a liquid or gas at room temperature)temperature)

Covalent CompoundsCovalent Compounds

Relatively weak force of attraction between Relatively weak force of attraction between moleculesmolecules

Remain as same molecule in water and will Remain as same molecule in water and will not conduct electricitynot conduct electricity

HH22O(l),O(l),

CC66HH1212OO22(s) (s) → → CC66HH1212OO22(aq) (aq)

Naming Covalent CompoundsNaming Covalent Compounds

All covalent compounds have two word All covalent compounds have two word names.  The first word is the first element names.  The first word is the first element in the formula and the second corresponds in the formula and the second corresponds to the second element in the formula to the second element in the formula except that "-ide" is substituted for the except that "-ide" is substituted for the end.  end. 

Rules for Naming Binary Covalent Rules for Naming Binary Covalent CompoundsCompounds

Rule 1 Rule 1

A binary covalent compound is composed of A binary covalent compound is composed of two different nonmetal elements. For two different nonmetal elements. For example, a molecule of chlorine trifluoride, example, a molecule of chlorine trifluoride, ClFClF33 contains 1 atom of chlorine and 3 contains 1 atom of chlorine and 3

atoms of fluorine.atoms of fluorine.

Rules for Naming Binary Covalent Rules for Naming Binary Covalent CompoundsCompounds

Rule 2.Rule 2. The second element in the name is The second element in the name is named as if it were an anion, i.e., by named as if it were an anion, i.e., by adding the suffix adding the suffix -ide-ide to the name of the to the name of the element.element.

Rules for Naming Binary Covalent Rules for Naming Binary Covalent CompoundsCompounds

Rule 3.Rule 3. If both elements are in the same If both elements are in the same group, the element with the bigger period group, the element with the bigger period number is written first in the name.number is written first in the name.

So , BrF is named “bromine fluoride", So , BrF is named “bromine fluoride", because bromine is the first element and because bromine is the first element and fluorine is the second element. fluorine is the second element.

Rules for Naming Binary Covalent Rules for Naming Binary Covalent CompoundsCompounds

Rule 4.Rule 4. Greek prefixes are used to indicate Greek prefixes are used to indicate the number of atoms of each nonmetal the number of atoms of each nonmetal element in the chemical formula for the element in the chemical formula for the compound.compound.

Exception: The only time “mono” is used Exception: The only time “mono” is used is with oxygenis with oxygen

Naming Covalent CompoundsNaming Covalent Compounds

If there is more than one atom of an element If there is more than one atom of an element in a molecule, we need to add prefixes to in a molecule, we need to add prefixes to these words to tell us how many are these words to tell us how many are present.  Here are the prefixes you'll need present.  Here are the prefixes you'll need to remember: to remember:

Prefixes for CovalentPrefixes for Covalent Number of atomsNumber of atoms PrefixPrefix

11 mono- mono- (use only for oxygen)(use only for oxygen)

22 di-di-

33 tri-tri-

44 tetra-tetra-

55 penta-penta-

66 hexa-hexa-

77 hepta-hepta-

88 octa-octa-

99 Nona-Nona-

1010 Deca-Deca-

Naming PracticeNaming Practice

SHSH2

P2S3

C4F10

NO

sulfur dihydride

diphosphorous trisulfide

tetracarbon decafluoride

nitrogen monoxide

Some important exceptionsSome important exceptionsTo the naming scheme occur because the To the naming scheme occur because the compounds were originally named before compounds were originally named before the methodical naming scheme above the methodical naming scheme above became widespread.  Nowadays, these became widespread.  Nowadays, these names are so common that they're names are so common that they're officially recognized: officially recognized:

HH22O is "water" O is "water"

NHNH33 is "ammonia" is "ammonia"

CHCH44 is "methane" is "methane"