Covalent Bonding

Chemical Bonding

…atoms share electrons to get a full valence shell

Covalent Bonds

C 2s2 2p2 (4 v.e–)

F 2s2 2p5 (7 v.e–)

both need 8 valence electrons for a full outer shell(octet rule)

1s2

1s2

Covalent bonding

F F

• Fluorine has seven valence electrons• A second F atom also has seven• By sharing electrons• Both end with full orbitals (stable octets)

8 Valence electrons

8 Valence electrons

Covalent Bonding

-

-

-

-

n = 1

O[He]2s22p4

n = 2

+

-

----

-

-

O2

Sharing of electrons to achieve a stable octet (8 electrons in valence shell).

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-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

O[He]2s22p4

Covalent/Molecular Compound

Silicon dioxide, SiO2, is a molecular compound. It is also a mineral called quartz (left).Quartz is found in nearly every type of rock. Most sand grains (center) are bits of quartz.Glass is made from sand.

A compound containing atoms of two or more elements that are bonded together by sharing electrons.

Covalent Bonding - True Molecules

Types of Bonds

Diatomic Molecule

Ammonia

Nitrogen

Water

Covalent vs. Ionic

Covalent

Transferelectrons

(ions formed)

+ / -

BetweenMetal andNonmetal

StrongBonds

(high melting point)

Shareelectrons

(polar vs. nonpolar)

BetweenTwo

Nonmetals

Weak Bonds

(low melting point)

Alike Different

Electronsare

involved

ChemicalBonds

Ionic

Different

Topic Topic

Lewis Structure

Lewis structure: a model of a covalent molecule thatshows all of the valence electrons

1. Two shared electrons make a single covalent bond,

four make a double bond, etc.

2. unshared pairs: pairs of un-bonded valence electrons

3. Each atom needs a full outer shell, i.e., 8 electrons. Exception: H needs 2 electrons

Lewis Structure

carbon tetrafluoride (CF4)

o

Co

o

o x

xx

x

x x

F x

o

Co

o

ox

xx

x

x x

F x

x x

x

x

x x

F x

x

xx

x

x

F x

x

x

xx

x x

F x

xCx

xx

x

x x

F

x x

x

x x

F x

x

xx

x F x

x

xx

x x

F x

x

covalent compounds = molecular compounds(have lower melting points than do ionic compounds)

Lewis Structure

o

Co

o o

x

Ho

Co

o oH x

x

H

xH

x H CH

H

H

H

x

xxx

x x

I xo

No

o o

o o

No

o ox

xxx

x x

I x

x x

xx

x x

I x

xxx

x x I x

x

o o

Nx

xxx

x x

I

x xx

x x

I x

xx

x x I x

x

o

o

Co

o o x

xxx

xO x

x

xxx

xO x

x

xxx

xO x

o

Co

o o O = C = O

x x

x x x x

x x

methane (CH4)

carbon dioxide (CO2)

nitrogen triiodide (NI3)