Valence Electrons l The electrons responsible for the chemical properties of atoms are those in the outer energy level. l Valence electrons - The electrons in the outer energy level or shell –the highest occupied energy level l Inner electrons -those in the energy levels below.

Keeping Track of Electrons l Atoms in the same column... –Have the same outer electron configuration. –Have the same valence electrons. l Easily found: same as the main group number on the periodic table. l Group 2: Be, Mg, Ca, Sr, Ba. –2 valence electrons

Electron Dot diagrams l A way of keeping track of valence electrons. l How to write them? l Write the symbol. l Put one dot for each valence electron l Don’t pair up until they have to. X

The Electron Dot diagram for Nitrogen l Nitrogen has 5 valence electrons. l First we write the symbol. N l Then add 1 electron at a time to each side. l Until they are forced to pair up.

Electron Configurations for Cations l Metals lose electrons to attain noble gas configuration (full outer shell). l They make positive ions (cations) l If we look at the electron configuration, it makes sense to lose electrons: l Na 2,8,1 1 valence electron l Na + 2,8 noble gas configuration

Electron Dots For Cations l Metals will have few valence electrons (usually 3 or less) Ca

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

Electron Dots For Cations l Metals will have few valence electrons l These will come off l Forming positive ions Ca 2+ noble gas configuration

Electron Configurations for Anions l Nonmetals gain electrons to attain noble gas configuration. l They make negative ions (anions) l Halide ions- ions from chlorine or other halogens that gain electrons l S (2,8,6) - 6 valence electrons l S 2- (2,8,8) - a noble gas configuration.

Electron Dots For Anions l Nonmetals will have many valence electrons (usually 5 or more) l They will gain electrons to fill outer shell. P P 3-

Stable Electron Configurations l All atoms react to achieve noble gas configuration. l Noble gases have 8 outer shell (valence) electrons. l This is also called the octet rule. Ar

Ionic Bonding  Between metals and non-metals  Transfer of electrons  Full outer shells  Oppositely charged ions created  Ions held to one another by electrostatic attraction  Giant structure formed

Ionic Bonds Characteristics of ionic compounds l Usually soluble in water l Electrical conductors when molten and when in aqueous solution. l High m.p. l Brittle, hard crystals

Ionic Bonding l Anions and cations are held together by opposite charges. l Ionic compounds are called salts. l Simplest ratio is called the formula unit. l The bond is formed through the transfer of electrons. l Electrons are transferred to achieve noble gas configuration.

Ionic Bonding NaCl

Ionic Bonding Na + Cl -

Ionic Bonding l All the electrons must be accounted for CaP

Ionic Bonding CaP

Ionic Bonding Ca 2+ P

Ionic Bonding Ca 2+ P Ca

Ionic Bonding Ca 2+ P 3- Ca

Ionic Bonding Ca 2+ P 3- Ca P

Ionic Bonding Ca 2+ P 3- Ca 2+ P

Ionic Bonding Ca 2+ P 3- Ca 2+ P Ca

Ionic Bonding Ca 2+ P 3- Ca 2+ P Ca

Ionic Bonding Ca 2+ P 3- Ca 2+ P 3- Ca 2+

Ionic Bonding = Ca 3 P 2 Formula 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 l Crystalline structure, usually solids l A regular repeating arrangement of ions in the solid l Ions are strongly bonded together. l Structure is rigid. l High melting points l Electrical conductors when melted l Electrical conductors in solution

Crystalline structure

Conducting electricity l Conducting electricity is allowing charges to move. l In a solid, the ions have charges but are locked in place. l Ionic solids are insulators. l When melted, the charged ions can move around. Melted ionic compounds conduct electricity. –To melt NaCl, it must get to about 800 ºC. l Dissolved in water (aqueous) the ions are now free to move and they conduct electricity.

Ionic solids are brittle

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

Solubility l Ionic solids are often (but not always) soluble in water. l Solubility usually (but not always) increases with increasing temperature.