BondingTypes of Bonds

PolarityIonic radius and ionic character

Why form bonds?

1. To get to a noble gas configuration (octet rule)– Ionic bonds (metal + nonmetal)• Metals want to lose their valence electrons• Nonmetals want to gain electrons

– Covalent bonds (nonmetals)• Both nonmetals want to share to reach a noble

gas configuration

2. To get to the lowest possible energy

Exceptions to the Octet Rule

• Hydrogen and helium want only 2

• Beryllium (metalloid) wants only 4

• Boron wants only 6

• 3rd energy level or below could be expanded if necessary– bonds using electrons in d orbitals

Reminders

• Electronegativity– How tightly an atom holds onto

electrons in a bond

– A measure of the attraction of an atom to another atom’s electrons in a bond

Reminders

• Ionic bond– Transfer of electrons

• Covalent bond– Sharing of electrons (a covalent bond is

always TWO shared electrons)

• Polarity – Unequal distribution of charge

Types of Bonds

• Based on the DIFFERENCE in electronegativity– System by Linus Pauling (1932)

– The more electronegative atom pulls the electrons in a bond

Types of Bonds

Types of Bonds

• Pauling’s system – Set fluorine as 4.0

– Differences in electronegativity• < 0.4 = nonpolar covalent• 0.4 – 2.0 = polar covalent• > 2.0 = ionic

Types of Bonds

• What it really means…– Same atom bonded to itself =

NONPOLAR

– Two different nonmetals bonded together = POLAR• The larger the difference, the more polar

the bond

– Metal and nonmetal = IONIC

More Ionic Bonding

• Coulomb’s Law– Describes the energy of interaction (attraction)

between a pair of ions

– Also called “lattice energy”

– C = Q1 x Q2 Q = charge of ion

r r = distance between centers of two

ions

More Ionic Bonding

• Coulomb’s Law– Examples:• NaCl vs. CaS – which has stronger

attraction / lattice energy?

• CaF2 vs. BaBr2 – which has stronger attraction/lattice energy?

More Ionic Bonding• Coulomb’s Law– Implications• A negative value means there is attraction

between the pair of ions, and you are getting lower energy by putting them together (good)• A positive value means there is repulsion,

and it’s endothermic (no bond formed)

• Charge larger influence than radius mathematically

More Ionic Bonding

• Ionic character– Measure of how ionic something is

– Can use locations on periodic table to predict• Shown – Which one is most ionic? NaF LiBr KBr NaI

More Covalent Bonding

• Two nonmetals sharing electrons

• Two different things bonded together is a polar bond

• Overall molecule may be polar or nonpolar based on symmetry

Bond Length Diagrams

• http://phet.colorado.edu/en/simulation/atomic-interactions

Bond Length Diagrams

• Balance of attractive/repulsive forces between nuclei and electrons

Bond Length Diagrams

• Location of dip = bond length

Bond Length Diagrams

• Size of dip = bond energy– Larger molecules = more energy– Double/triple bonds = more energy

More Covalent Bonding

• Nonpolar = symmetrical, equal pull in every direction

• Polar = not symmetrical, greater pull in one direction

• Polar and nonpolar don’t mix

More Covalent Bonding• Types of covalent bonds (rubber bands)

– Single bond• One shared pair of electrons• Sigma bond• Longest bond length• Lowest bond energy

– Double bond• Two shared pairs of electrons• Sigma bond + pi bond• Shorter bond length than single• Higher bond energy than single (less stable)

– Triple bond• Three shared pairs of electrons• Sigma bond + 2 pi bonds• Shortest bond length• Highest bond energy

More Covalent Bonding

• LOTS more to come with drawing and what the shape of each of these molecules is

• Stay tuned….

Lewis Structures

• G.N. Lewis (1916)

– Used lines and dots to represent bonding and valence electrons

– A line was a covalent bond (2 e-)– A dot represents each valence electron

Lewis Structures

• Atoms– The number of dots is equal to the

number of valence electrons in an atom– Fill each side of the symbol before

pairing any electrons (except H and He)

Examples:

Lewis Structures

• Ionic Compounds1. Draw symbol for each atom2. Transfer electrons until each metal has

0 valence electrons and each nonmetal has 8 valence electrons

3. Add multiple atoms of each type if necessary

Lewis Structures

• Ionic Compounds– Examples