1. Unit 4 – Introduction to Bonding Valence Electrons Ionic Bonding

2. Chemical Bonds The following is true for chemical bonds: Always involves a +/- attraction. Occurs when one electron is simultaneously attracted by two nuclei. Bonds release energy when they are made. Energy is required to break a bond. Bonds involve only the valence electrons.

3. Valence and Electron Dot Notation A way to show the valence electrons that an element has. Group# valence e-’sElectron configuration Dot Diagram 11s1s1 X. 22s2s2.X..X. 133s2p1s2p1.. X. 144s2p2s2p2.. X..

4. Group# valence e-’sElectron configuration Dot Diagram 155s2p3s2p3. :X.. 166s2p4s2p4. :X:. 177s2p5s2p5.. : X... 188s2p6s2p6.. :X:..

5. Octet Rule Bonds between atoms in compounds tend to form so each atom has the electron configuration of a noble gas. (That means 8 electrons in the highest energy level “s” and “p” orbitals) The atom does this by Gaining, Losing or Sharing electrons.

6. Ions Ions form based on the Octet rule – Loss of valence electrons results in a (+) charged cation. – Cations are always metals. – Gain of valence electrons results in (-) charged anion – Anions are always non-metals.

7. Ionic Bonds Electrons are transferred from a metal to a non-metal. Ionic bond is due to electrostatic attraction. Ionic compounds are made up of a positive ion (cation) and a Negative ion (anion) The general formula for an ionic compound is Cation Anion Most ionic compounds are crystalline solids at room temperature.

8. Ionic Bonding Examples Nonmetals take electrons from metals until an octet is established. NaClNa + Cl 1-

9. Examples of Ionic bonds Na + Cl [ Na] + [ Cl ] 1- Formula: NaCl Mg + O [Mg] 2+ [ O ] 2- Formula: MgO

10. Ionic Compound Formulas The overall charge of an ionic compound is zero. Ex. NaCl, MgO This means that the positive and negative charges within an ionic compound must balance out to be zero. No Charges are ever written in the ionic compound formula!!!

11. Writing the Formulas of Ionic Compounds Write the symbols for the positive and negative ions (cation always is first). Ca Cl The charges are written as superscripts. Ca 2+ Cl 1- Criss-cross the charges into subscripts (Leaving out the + and – signs). Ca 2+ Cl 1- becomes CaCl 2 Simplify the numbers to lowest terms. (if needed) CaCl 2 Finally, remember that the number “1” can never be a subscript.

12. Example: Mg and O 1. Write Charges Mg 2+ O 2- 2. Criss- Cross the charges to become subscripts. Mg 2+ O 2- This forms Mg 2 O 2 Now we notice that both elements have “2” as subscript, so we reduce to lowest terms It becomes: MgO