AP Chemistry: Unit 2 BONDING

Ionic

Electrostatic attraction between ions

Covalent

Sharing of electrons

Metallic

Sea of electrons

Lattice energy

completely separate a mole of solid ionic compound into its gaseous ions

LATTICE ENERGY INCREASES WITH

increased charge of ions

decreased size of ions

Covalent bonding have several interactions…

• attraction between electrons and nuclei

• repulsions between electrons

• repulsions between nuclei

Formation of bonds is

exothermic

Breaking of bonds is

endothermic

Polar Covalent Bonds

Electrons are NOT always shared equally, more electron density on the electron that is pulling HARDER

What determines whether somethin is pulling harder?

electronegativity (increase from left to right, increase from bottom to the top)

When atoms share electrons unequally,

a bond dipole results

A dipole moment

produced by two equal but opposite charges separated by a distance r

What determines polar covalent strength?

The greater the difference in electronegativity, the stronger the polarity of the bond

Lewis Structures

Representation of molecules showing all electrons, bonding and non bonding

How to write Lewis Structures

• fill octet

Central atom in Lewis Structure is the _____ electronegative (that isn’t hydrogen)

LEAST

FORMATION OF MULTIPLE BONDS WITH LEWIS STRUCTURES

ONLY C,N,O,P, and S can form multiple bonds

Resonance

multiple structures can used to describe the same molecule

Resonance structure

delocalized, can move to any of the structures at any time

How determine the best lewis structures?

FORMAL CHARGES

How do we determine formula charges?

COUNT ITS ELECTRONS IN LONE PAIRS and HALF OF THE ELECTRONS IT SHARES WITH OTHER ATOMS, subtract that from valence electrons

If using formal charge to determine which structure is best and it’s impossible to get all 0 formal charges,

you choose the structure where the most electronegative element has the MOST electronegative element and the MOST negative charge

EXCEPTION TO OCTET RULE

-ions/molecules with an odd number of electrons

-ions or molecules with less than an octet

-ions or molecules with more than eight valence electrons (an expanded octet)