ch. 6 chemical bonding valence a chemical bond occurs when valence electrons are lost, gained,...

Ch. 6 Chemical Bonding

A Chemical Bond occurs when valencevalence electrons are lost, gained, transferred or shared between two or more atoms.

The Octet RuleAtoms tend to gain, lose, or share electrons

until they have eight valence electrons.

This is called a “Stable Octet.”

Why Do Atoms form a Why Do Atoms form a Bond?Bond?

To form a state of lower potential energyTo form a state of lower potential energy. Bonded atoms require less energy

To become more stableTo become more stable. A Stable Octet of 8 electrons resembles the Nobel Gases.

The Three types of The Three types of BondsBonds

Ionic Bond –

Transfer of electrons from a

cation to an anion.

The Three types of BondsThe Three types of Bonds

Covalent Bond Sharing of electrons so that all atoms involved

maintain a Stable octet.

Three types of BondsThree types of Bonds

Metallic Bond Cations attracted to other Cations

by a sea of electrons

surrounding all of the positive ions.

Sea of electrons

Identifying the Bond

When MetalsMetals bond to Non-MetalsNon-Metals they will form an Ionic Bond

When Non-MetalsNon-Metals bond to other Non-MetalsNon-Metals they will form a

Covalent Bond

When MetalsMetals bond to other MetalsMetals they will form a Metallic Bond

Lewis Dot Diagrams

Lewis symbols show the valence electrons as dots arranged around the atomic symbol.

hydrogen:

sodium:

chlorine:

Na

H

Cl

Using Lewis Dot Diagrams for Ionic compounds and Covalent

molecules• Formation of sodium chloride:

• Formation of hydrogen chloride:

When filling up valence shells make sure all non-metals finish with a

stable octet. If possible all elements should finish with an octet.

Na + Na+ [ ]Cl

Cl

H + Cl

Cl

H

Basic Formula WritingWhen writing a formula the most metallic

element is written first.(leftmost on the P.table)Ex. NaCl and MgO not “ClNa” or “OMG”Ex. NaCl and MgO not “ClNa” or “OMG”

Subscripts are to be used to represent the number of elements or ions needed to make all species maintain a octet.

Ex. Ex. HH22O or AlBrO or AlBr33

(A subscript of 1 is understood and is not (A subscript of 1 is understood and is not written.)written.)

Bond Determination Using e-dot diagrams determine the formulas for the following.Using e-dot diagrams determine the formulas for the following.

Metal to Non-Metal Metal to Non-Metal Ionic Ionic Non-Metal to Non-Metal Non-Metal to Non-Metal Covalent Covalent

Ionic IonicIonicIonicIonic CovalentCovalent

HFCaCl2Al2O3

Cu3N or Cu3N2

K3PNBr3

As2S3

1. H + F2. Ca + Cl 3. Al + O4. * Cu + N5. K + P6. N + Br7. As + S

When writing the formula of a compound or molecule the more metallic element is always

written 1st ( furthest to the left)

Determining FormulasThe Criss-Cross Method

A short cut to formula writing can be accomplished using the oxidation or

charge of ions to determine the chemical formulas of compounds.

• Examples Na+1 + O-2

Ca+2 + P-3

C+4 + O-2

Na2O

Ca3P2

C2O4 reduced to CO2