_____________ Bond• Between nonmetallic elements of similar

electronegativity.• Formed by sharing electron pairs• Stable non-ionizing particles, they are not

conductors at any state• FORM MOLECULES• Examples; O2, CO2, C2H6, H2O, SiC• Bonds in all the polyatomic ions and

diatomics are all covalent bonds

_____________ Chemical Bonds• According to the Lewis model

– an atom may lose or gain enough electrons to acquire a filled valence shell and become an ion. An ionic bond is the result of the force of attraction between a cation and an anion.

– an atom may share electrons with one or more other atoms to acquire a filled valence shell. A covalent bond is the result of the force of attraction between two atoms with relatively close electronegativities that share one or more pairs of electrons.

Material from karentimberlake.com and

H. Stephen Stoker

• If the difference in electronegativities is between:– 1.7 to 4.0: Ionic– 0.3 to 1.7: Polar Covalent– 0.0 to 0.3: Non-Polar Covalent

Try KF, H2O, Cl2

____________ or _________ ???

C. Johannesson

A. __________ of Bond Formation• Potential Energy

– based on position of an object– low PE =

high stability

C. Johannesson

Bond Energy

A. Energy of Bond Formation

Bond Length

• Bond Energy– Energy required to break a bond

C. Johannesson

A. Energy of Bond Formation

• Bond Energy– Short bond = ____________ bond energy

Drawing ________ Structures

1. Determine the number of valence electrons in the molecule

2. Decide on the arrangement of atoms in the molecule

3. Connect the atoms by single bonds

4. Show bonding electrons as a single line; show nonbonding electrons as a pair of Lewis dots

5. In a single bond, atoms share one pair of electrons; in a double bond, they share two pairs, and in a triple bond they share three pairs.

Covalent Bonds

Two nonmetal atoms form a covalent bond because they have less energy after they bonded

H + H H : H = HH = H2

hydrogen molecule

C. Johannesson

B. Lewis Structures• Electron Dot Diagrams

– show valence e- as dots– distribute dots like arrows

in an orbital diagram– 4 sides = 1 s-orbital, 3 p-orbitals– EX: oxygen

X

C. Johannesson

B. Lewis Structures• Octet Rule

– Most atoms form bonds in order to obtain 8 valence e-

– Full energy level stability ~ Noble Gases

Ne

Double Covalent Bond

2 pairs of electrons are shared between 2 atoms

Example O2

Triple Covalent Bond

3 pairs of electrons are shared between 2 atoms

Example N2

Lewis Structures

Other molecules having single covalent bonds

H2O

The hydrogens share their electrons w/ oxygen so that O has 8 e- and each H has 2 e-

Covalent Bonds in NH3

Learning Check• Examples

– draw a Lewis structure for hydrogen peroxide, H2O2

– draw a Lewis structure for methanol, CH3OH

– draw a Lewis structure for acetic acid, CH3COOH

C. Johannesson

C. Molecular Nomenclature• Prefix System (binary compounds)

1. Less e-neg atom comes first.

2. Add prefixes to indicate # of atoms. Omit mono- prefix on first element.

3. Change the ending of the second element to -ide.

C. Johannesson

PREFIXmono-di-tri-tetra-penta-hexa-hepta-octa-nona-deca-

NUMBER123456789

10

C. Molecular Nomenclature

C. Johannesson

CCl4

N2O

SF6

C. Molecular Nomenclature

C. Johannesson

arsenic trichloride

dinitrogen pentoxide

tetraphosphorus decoxide

C. Molecular Nomenclature

C. Johannesson

N O F

Cl

Br

I

H

C. Molecular Nomenclature

• The Seven Diatomic Elements

Br2 I2 N2 Cl2 H2 O2 F2

Material from karentimberlake.com and

H. Stephen Stoker

__________ Elements

• Elements that are naturally in molecules with 2 atoms each.

• “H NO Halogens” • Existing as diatomic molecule yields a stable octet• Gases that exist as diatomic molecules are H2, F2,

N2, O2, Cl2, Br2, I2

• Examples Fluorine & Bromine

Material from karentimberlake.com and

H. Stephen Stoker

Common Names:

Learning Check Fill in the blanks to complete the following names of covalent compounds.

CO carbon ______oxide

CO2 carbon _______________

PCl3 phosphorus _______chloride

CCl4 carbon ________chloride

N2O _____nitrogen _____oxide

© Karen Timberlake

Material from karentimberlake.com and

H. Stephen Stoker

Learning Check A. P2O5

B. Cl2O7

C. Cl2

Bond Polarity: PolarPolar covalent bondElectrons are shared between different

nonmetal atoms Due to differing electronegativities, some

elements will hold the e- more tightly than the other in a covalent bond, therefore one side of the molecule is partially (+) and one side of the molecule is partially (-).

Examples:Cl2O SO Cl3N

Material from karentimberlake.com and

H. Stephen Stoker

Material from karentimberlake.com and

H. Stephen Stoker

Chemical Bonding: The Covalent Bond Model

← Fig. 5.12(a) In the nonpolar covalent bond present, there is a symmetrical distribution of electron density. (b) In the polar covalent bond present, electron density is displaced because of its electronegativity.

C. Johannesson

+ -

+

B. Lewis Structures• ____________ Covalent - no charges

• _________ Covalent - partial charges

Chemical Bonding: The Covalent Bond Model

Fig. 5.13 (a) Methane is a nonpolar tetrahedral molecule. (b) Methyl chloride is a polar tetrahedral molecule.

- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

C. Johannesson

IONIC COVALENTBond Formation

Type of Structure

Solubility in Water

Electrical Conductivity

OtherProperties

e- are transferred from metal to nonmetal

high

yes (solution or liquid)

yes

e- are shared between two nonmetals

low

no

usually not

MeltingPoint

crystal lattice true molecules

B. Types of Bonds

Physical State solid liquid or gas

odorous