Covalent Bonding

Quick ReviewCovalent bond – two atoms held together by

sharing electrons -- Usually occurs between nonmetals.

Octet Rule – chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest energy level.

Valence electrons – the electrons in an atom’s outer energy level

Electron-dot diagramsshows an atom’s valence electrons

Draw electron-dot diagrams for:

N F Na O

New TermsMolecule – a neutral group of atoms held

together by covalent bonds

Molecular formula – shows the types and numbers of atoms combined in a single molecule (ex: H2O, CO2, H2SO4)

Diatomic molecule – molecule containing two atoms

(Examples: H2, N2, O2, F2, Cl2, Br2, I2, HCl, NO)

Using Electron Dot Notation diagramsH2 molecule (nonpolar covalent = EQUAL sharing)H· ·H H : H Structural formula: H-H (Use single line

for e- pair)

the hydrogen orbitals

overlap

· · · ·

F2 molecule

·· ·· ·· ·· : F· ·F : : F : F :

·· ·· ·· ··Structural formula: F-FEach fluorine atom has 8 electrons in the

outer energy level.

HCl molecule

H Cl H ClH – ClEach atom now has a filled outer energy level.

Usually there will be more than two atoms bonding together.Water H2O Each hydrogen atom is bonded to oxygen

atom

H O H O

H H Structural formula H O H

Try these molecules: NH3, ClI, H2O2NH3 moleculeEach hydrogen atom is bonded to the

nitrogen atom.

H N H

H

ClI molecule (chlorine and iodine)

Cl I Cl I

Structural formula Cl – I

H2O2 moleculeH O H O O H O H

Structural Formula H O O H

Bond Length and EnergyBond length – the average distance between

bonded atoms

Bond energy – energy required to break a chemical bond and form neutral isolated atoms.

Single BondsSingle bonds – a covalent bond produced by

the sharing of one pair of electrons between two atoms.

All of the examples so far have been of single

bonds.

Double BondsDouble bonds – a covalent bond produced by

the sharing of two pairs of electrons between two atoms.

O2 molecule

O O Structural formula O=O

Triple BondsTriple bonds – a covalent bond produced by

the sharing of three pairs of electrons between two atoms.

N2 molecule

N N Structural formula N≡N

RelationshipsBetween bond length and # of bonds:

As the number of bonds INCREASES, the bond length DECREASES

Between bond energy and # of bonds:As the number of bonds INCREASES, the

energy required to break those bonds INCREASES

How to draw Lewis Structures (AKA electron dot diagrams)

Two Types of Electron Pairs:Shared Pair – a bonded pair; exists between 2

atoms in the same molecule. Represented by a straight line between the bonded atoms.

Unshared Pair – a lone pair; belongs entirely to one atom. Represented by a pair of dots on that atom.

Rules for Drawing Lewis Structures:

1) Draw a skeleton structure for the compound by joining the atoms with single bonds (single straight lines). The central atom is usually:

a) The one with the highest number of valence electrons

b) The largest atom

c) The least electronegative atom

Rules for Drawing Lewis Structures:

d) Hydrogen will NEVER be a central atom

e) Oxygen will only be central if bonded to H or F

Rules for Drawing Lewis Structures:2) Count/Tally the number of total valence

electrons

3) Determine the number of electron pairs by dividing the total number of valence electrons (step #2) by 2

4) Determine the number of available electron pairs by subtracting the number of pairs already used in the skeleton structure

Rules for Drawing Lewis Structures:5) Place LONE PAIRS around the terminal/end

atoms. If any pairs are left, put them as lone pairs on the central atom

6) Check the OCTET RULE. If the central atom is not yet surrounded by 8 electrons, form multiple bonds.

Rules for Drawing Lewis Structures:Example: draw the Lewis Structure for

Carbon Dioxide

Rules for Drawing Lewis Structures:Draw the Lewis Structure for Methanal

(Formaldehyde) CH2O

Rules for Drawing Lewis Structures:CF4 PCl3

OCl2 O2