2. AN IONIC BOND IS FORMED WHEN ONE OR MORE ATOMS LOSE THEIR VALENCE ELECTRONS AND ANOTHER ONE OR MORE ATOMS GAIN THESE SAME ELECTRONS TO ACHIEVE NOBLE GAS ELECTRON CONFIGURATIONS. IN IONIC BOND FORMATION, THE NUMBER OF ELECTRONS LOST MUST EQUAL THE NUMBER OF ELECTRONS GAINED. ELECTRONEUTRALITY MUST BE MAINTAINED.

3. AN ION IS AN ATOM OR GROUP OF ATOMS WITH A CHARGE. THE NET ELECTRIC CHARGE ON AN ION IS THE NUMBER OF PROTONS MINUS THE NUMBER OF ELECTRONS. IT IS THE ELECTROSTATIC FORCE OF ATTRACTION THAT HOLDS IONIC COMPOUNDS TOGETHER. IN AN IONIC COMPOUND, THE NUMBER OF POSITIVE CHARGES HAS TO EQUAL THE NUMBER OF NEGATIVE CHARGES.

4. POSITIVE IONS ARE CALLED CATIONS. NEGATIVE IONS ARE CALLED ANIONS. THE NUMBERS OF ATOMS OF VARIOUS ELEMENTS INVOLVED IN AN IONIC COMPOUND ARE DETERMINED BY: 1)THE TOTAL ELECTRICAL CHAGE MUST BE ZERO 2)ALL THE ATOMS HAVE NOBLE GAS CONFIGURATION

5. IN IONIC COMPOUNDS, YOU DON’T REALLY HAVE MOLECULES, AS THE ENTIRE CRYSTAL IS MADE UP OF ALTERNATING POSITIVE AND NEGATIVE IONS. SO, WE TALK OF FORMULA UNITS RATHER THAN MOLECULES. FORMULA UNITS ARE THE SMALLEST WHOLE NUMBER RATIO OF THE IONS IN THE COMPOUND.

6. IN COVALENT COMPOUNDS, PAIRS OF ELECTRONS ARE SHARED. THIS PRODUCES MOLECULES – GROUPS OF ATOMS CHEMICALLY COMBINED WHICH BEHAVE AS A UNIT.

7. An example would be when hydrogen reacts with oxygen. In the resulting molecule, there is a shared pair of electrons between each hydrogen and the oxygen. This gives each hydrogen a share in two electrons - a complete outer shell.

8. And, it gives oxygen a share in 8 electrons - a complete outer shell. A shared pair of electrons between two atoms is called a single covalent bond. We could also represent this as a single line. H O This would be the structural formula.

9. In reality, the electron clouds would surround the nuclei of both atoms, and the molecule would probably look more like the model below: For convenience, we simply write the formula for water as H 2 O.

10. Most molecular substances are formed between nonmetals. Several elements exist in nature as diatomic molecules. H 2 F 2 Cl 2 I 2 O 2 N 2 Formulas that show the actual number of atoms in a molecule are called molecular formulas. Formulas that indicate the simplest whole number ratios of atoms present are called empirical formulas. For ionic compounds, we are generally using the empirical formulas.

11. CHARACTERISTICS OF COVALENT COMPOUNDS 1.Have low melting points and boiling points - many would be gases or liquids at room temperature. 2.Would not conduct electricity. 3.Many are not soluble in water or other polar solvents.

12. Rules for naming binary molecular compounds: 1.The name of the element farthest to the left in the periodic table is given first. 2.If both elements are in the same group, the lower one is named first. 3.The name of the second element is given an -ide ending. 4.Greek prefixes are used to indicate the number of atoms present. Examples: Cl 2 O dichlorine monoxide NF 3 nitrogen trifluoride N 2 O 4 dinitrogen tetroxide

13. Name the following compounds: a.SO 2 b.PCl 5 c.N 2 O 3 Give the chemical formula for: a.Silicon tetrabromide b.Disulfur dichloride