1. Unit 7: Compounds and Chemical Reactions
Section 7.2
Ionic Bonds
March 9, 2011
Page 175/177

2. Ionic compounds
Ionic bonds are bonds in which electrons are transferred from one atom to another.
Sodium and chlorine form an ionic bond because the positive sodium ion is attracted to the negative chloride ion.

3. Ions An ion is an atom with a charge
When an atom gives an electron (-) to another atom, it becomes a positive ion
Metals make positive ions.
When an atom gets an electron (-) from another atom, it becomes a negative ion
Non-metals make negative ions.

5. Ionic Compounds
Since pluses like minuses, positive ions are attracted to negative ions - this is what holds ionic compounds together.
Atoms in ionic compounds don’t hang out alone – they group together in repeating patterns called crystals
How atoms line up in forming bonds determine the shape of the crystal

6. Crystalline Solids
If the atoms are in an orderly, repeating pattern, the solid is called crystalline.
Examples of crystalline solids include salts, minerals, and metals.

7. Oxidation numbers
An oxidation number indicates the charge on the remaining atom (ion) when electrons are lost, gained, or shared in chemical bonds.
A sodium atom always ionizes to become Na+ (a charge of +1) when it combines with other atoms to make a compound.
Therefore, we say that sodium has an oxidation number of 1+.
What is the most common oxidation number for nitrogen?

9. Al2O3 Li2S Calculating Formulas
To figure out the formula for an ionic compound, use the Criss Cross method:
Write the oxidation numbers above the element
The oxidation number for the first element is the subscript for the second and vice versa (criss cross)
Reduce common factors and remember you don’t write ones +3 -2 +1 -2
Al2O3
Li2S

10. Electrons and chemical bonds
Chemical bonds are formed only between the electrons in the highest unfilled energy level.
These electrons are called valence electrons.

12. Electrons and chemical bonds
Going from left to right across a period each new element has one more valence electron than the one before it.
How many valence electrons does nitrogen have?

13. Lewis dot diagrams
A clever way to keep track of valence electrons is to draw Lewis dot diagrams.
A dot diagram shows the element symbol surrounded by one to eight dots representing the valence electrons.
What is the dot structure for nitrogen?

15. Predicting a chemical formula
When elements combine in molecules and ionic compounds, the total electric charge is always zero.

16. As heat energy is added to ice, the temperature increases until it reaches 0°C.
Then the temperature stops increasing.
As you add more heat, more ice becomes liquid water but the temperature stays the same.
This is because the added energy is being used to break the intermolecular forces and change solid into liquid.
Once all the ice has become liquid, the temperature starts to rise again if more energy is added.