Valence Electrons The electrons responsible for the

chemical properties of atoms are those in the outer energy level.

Valence electrons - The electrons in the outer energy level or shell

–the highest occupied energy level Inner electrons -those in the energy

levels below.

Keeping Track of Electrons Atoms in the same column...

–Have the same outer electron configuration.

–Have the same valence electrons. Easily found: same as the main group

number on the periodic table. Group 2: Be, Mg, Ca, Sr, Ba.

–2 valence electrons

Electron Dot diagrams A way of keeping track of

valence electrons. How to write them? Write the symbol. Put one dot for each

valence electron Don’t pair up until they

have to.

X

The Electron Dot diagram for Nitrogen

Nitrogen has 5 valence electrons.

First we write the symbol.

NThen add 1 electron at a time to each side.Until they are forced to pair up.

Electron Configurations for Cations

Metals lose electrons to attain noble gas configuration (full outer shell).

They make positive ions (cations) If we look at the electron configuration,

it makes sense to lose electrons: Na 2,8,1 1 valence electron Na+ 2,8 noble gas configuration

Electron Dots For Cations Metals will have few valence

electrons (usually 3 or less)

Ca

Electron Dots For Cations Metals will have few valence electrons These will come off

Ca

Electron Dots For Cations Metals will have few valence electrons These will come off Forming positive ions

Ca2+noble gas configuration

Electron Configurations for Anions

Nonmetals gain electrons to attain noble gas configuration.

They make negative ions (anions) Halide ions- ions from chlorine or other

halogens that gain electrons S (2,8,6) - 6 valence electrons S2- (2,8,8) - a noble gas configuration.

Electron Dots For Anions Nonmetals will have many valence

electrons (usually 5 or more) They will gain electrons to fill outer shell.

P P3-

Stable Electron Configurations All atoms react to achieve noble gas

configuration. Noble gases have 8 outer shell

(valence) electrons. This is also called the octet rule.

Ar

Ionic BondingBetween metals and non-metalsTransfer of electronsFull outer shellsOppositely charged ions createdIons held to one another by

electrostatic attractionGiant structure formed

Ionic Bonds

Characteristics of ionic compounds Usually soluble in water Electrical conductors when molten

and when in aqueous solution. High m.p. Brittle, hard crystals

Ionic Bonding Anions and cations are held

together by opposite charges. Ionic compounds are called salts. Simplest ratio is called the formula

unit. The bond is formed through the

transfer of electrons. Electrons are transferred to achieve

noble gas configuration.

Ionic Bonding

Na Cl

Ionic Bonding

Na+ Cl-

Ionic Bonding All the electrons must be accounted for

Ca P

Ionic Bonding

Ca P

Ionic Bonding

Ca2+ P

Ionic Bonding

Ca2+ P

Ca

Ionic Bonding

Ca2+ P 3-

Ca

Ionic Bonding

Ca2+ P 3-

Ca P

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ca

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ca

Ionic Bonding

Ca2+ P 3-

Ca2+P

3-

Ca2+

Ionic Bonding

= Ca3P2Formula Unit

Calcium Phosphide

Classwork problems (a)Show the bonding between the following

1. Magnesium and Oxygen

2. Potassium and Chlorine

3. Calcium and Fluorine

4. Lithium and Nitrogen

5. Aluminium and Fluorine

Properties of Ionic Compounds Crystalline structure, usually solids A regular repeating arrangement of

ions in the solid Ions are strongly bonded together. Structure is rigid. High melting points Electrical conductors when melted Electrical conductors in solution

Crystalline structure

Conducting electricity Conducting electricity is allowing charges to

move. In a solid, the ions have charges but are locked

in place. Ionic solids are insulators. When melted, the charged ions can move

around. Melted ionic compounds conduct electricity.– To melt NaCl, it must get to about 800 ºC.

Dissolved in water (aqueous) the ions are now free to move and they conduct electricity.

Ionic solids are brittle

+ - + -+- +-

+ - + -+- +-

Ionic solids are brittle

+ - + -

+- +-+ - + -

+- +-

Displacing the top layer (diagram) puts ions of the same charge near one another creating strong repulsion that breaks the crystal apart.

Solubility Ionic solids are often (but not always)

soluble in water. Solubility usually (but not always)

increases with increasing temperature.