Building Science Champions

Covalent Bonds

Describe how covalent bonds form.Identify the properties of molecular

compounds.Distinguish between polar and nonpolar

bonds, and between polar and nonpolar compounds.

Objectives

Covalent bondDouble bondMolecular compoundPolarNonpolar

Key Terms

Co = share valent = valence electrons = shared electrons

A covalent bond is a chemical bond formed when two atoms SHARE electrons.

Form between 2 or more nonmetals. Oxygen, carbon, nitrogen and the halogen

family frequently bond with other nonmetals by sharing electrons.

Covalent Bond

F + F F F

Each fluorine has 7 valence electronsThey share 1 pairWhen you count the valence electrons, you count the

shared pair each time.By sharing they have 8 valence electrons. In a covalent bond, both atoms attract the 2

shared electrons at the same time.

Fluorine

Shared pair of electrons

There are 3 types of pairing for covalent bonds:

Single Bond – shares one pair of electronsDouble Bond – shares two pairs of electronsTriple Bond – shares three pairs of electrons

F F O O N N

Number of Bonds

Single Bond

Double Bond

Triple Bond

Properties Molecular Compounds

consist of molecules having covalently bonded atoms.

Weaker bonds than ionic bonds

Poor conductors of electricity

No charged particlesUsed for insulation: ie.

rubber and plastic

Compound Formula Melting Pt (0C)

Boiling Pt (0C)

Water H2O 0 100

Methane CH4 -182 -164

Carbon Dioxide

CO2 - -78.6*

Ammonia

NH3 -77.7 -33.6

Rubbing Alcohol

C3H7OH -89.5 82.4

Sugar C12H22O

11

185-186

decomposes

Molecular Compounds Melting and Boiling Points of

Molecular Compounds

*Carbon Dioxide changes from a solid to a gas

PolarA covalent bond

where electrons are not shared equally.

H O H

Pull is toward oxygen = Polar

A covalent bond where electrons are shared equally.

F Cl

Pull in opposite directions = nonpolar

Sharing of Electrons

Nonpolar

+ - +

Some atoms pull more strongly on the shared electrons than other atoms do. As a result, the electrons move closer to one atom, causing the atoms to have a slight electrical charge.

One electron is being pulled closer to one atom causing the atom losing an electron to become slightly positive and the one receiving an electron is slightly negative.

Unequal Sharing of Electrons

Valence electrons are shared between covalent bonds

Electrons are rapidly moving from one atom to another giving an atom a slight positive or negative charge

Review

Draw dot diagrams for the following compounds and write if they are Ionic or Covalent. IF THEY ARE COVALENT WRITE IF THEY ARE polar or nonpolar and what number bond they have. N2 MgO CO2O2 NaCl CaSRbI NH3 CH4Al2O3

Higher difficulty

Your Turn

ReferencesAnderson, M. et all (2012) Physical Science.

McGraw-Hill: ColumbusFrank, D.V et al (2001). Physical Science.

Prentice Hall: New Jersey