Covalent Bonding & PolarityChapter 6.2

Chemical Bonding Ionic Bond – Force that holds cations

and anions together and which involves the transfer of electrons. Occurs between a metal and a nonmetal.

Ionic Bonding Elements achieve stable electron configurations

by transferring or sharing electrons between atoms

Transferring Electrons - Those with <4 valence electrons “LEND” them

(Metals)These elements “lose” valence electrons

OR Those with >4 valence electrons “BORROW”

them (Nonmetals)These elements “gain” electrons

Chemical BondingWhat do you think will happen

when 2 nonmetals bond? Will there be a transfer of electrons?

Why?

FF

Covalent Bonding When two nonmetals meet - one atom is

NOT strong enough to take electrons from the other! So they must share them Covalent

Bond!

Covalent bond - is a chemical bond in which two atoms share one or more pairs of valence electrons.

Covalent BondingElectrons want to be in pairs –

4 pairs of 2 to fulfill the octet rule.Paired electrons are ‘happy’!Unpaired electrons are ‘sad’

Paired or Unpaired

Paired Electron Unpaired Electron

How it Works

+

How it works!

Sharing Creates a Bond

F F

Outer Level Still only hold 8!!!!

Electron Configuration & Lewis Dot Structures

All 3 figures represent the same thing!BAR = Bond of shared electrons

F F

F F F F

This illustration shows four ways to represent a covalent bond between two hydrogen atoms.

As a space shuttle lifts off, it leaves a water vapor trail. A reaction of hydrogen and oxygen produces the water.

Diatomic means “two atoms”.

Many nonmetal elements are often found as diatomic molecules.

Atoms of same element share bonding electrons equally.

Balanced

Covalent Bonds

Single Bond

FFF F OR

Each atom now “Feels Like” it has 8 valence electrons!

Single Bond =

• One Pair of e- Shared Between Two Atoms.• Each atom gives one e- to the shared pair

How Will These Two Bond?

Oxygen and Oxygen

O O

Double Bond

OR

•Two Pairs of Electrons are Being Shared•Each atom gives one e- to each shared pair

O O

O O

Another example!Sharing Creates a Bond

CO2

Since each are sharing two pairs Double Bond!

CO O

How Will These Two Bond?Nitrogen and Nitrogen

N NN

Triple Bond

OR

• Three Pairs of Electrons Being Shared

N N

N N

Covalent Bonding Problems:

Make a molecule out of Oxygen and two

Fluorine

Covalent Bonding Problems:

FOF

Formula: OF2

OF F

Covalent Bonding Problems:

Try Carbon and two Oxygen

Covalent Bonding Problems

OCO

CO OFormula: CO2

Unequal Sharing of Electrons Diatomic compounds share electrons

equally. Equal forces pulling on the shared

electrons

What happens when atoms do NOT share electrons equally? Unequal forces pulling on the shared

electrons

Polar Covalent Bond:Electrons not transferred from one atom to another, but…

Atom with greater attraction for electrons has a partial negative chargeOther atom has a partial positive charge.

Types of atoms determine whether a molecule is polar or non-polar.

Unequal Sharing of Electrons

Unequal Sharing of ElectronsElectronegativity = Atom’s attraction for

electrons Bigger value stronger attraction

Electronegativity trends (attraction for electrons): Right side of periodic table: high

Exception for noble gases (Group #8A) - none Left side of periodic table: low Top of a group: higher Bottom of a group: lower

Prof Mokeur’s Periodic Table

Shared electrons in a hydrogen chloride molecule spend less time near the hydrogen atom than near the chlorine atom.

Unequal Sharing of Electrons

How to predict what type of bond will form between two

atoms:Non-polar covalent

Electronegativity difference is <0.5Polar covalent

Electronegativity difference is >0.5 and <2.0

Ionic bondElectronegativity difference is >2.0

ExamplesBoron and Hydrogen

Electronegativities: B = 2.0 H = 2.1Difference: 0.1 non-polar covalent

Potassium and Iodine: Electronegativities: K = 0.8 I = 2.7Difference: 1.9 polar covalent

Sodium and ChlorineElectronegativities: Na = 0.9 Cl = 3.0Difference: 2.1 ionic