1. Periodic Table: Molecules & Ions
4-ch1_pt3

2. Reminder: Lewis Notation
Definition: A simplified representation of the atom where only the valence electrons are shown
Examples:
Sodium Argon Carbon Fluorine

3. Forming Molecules
Most elements do not exist in their elemental form (all alone) in nature
Most atoms BOND with other atoms to form MOLECULES
Molecule: a group of two or more atoms that are chemically bonded together

4. Why do Molecules Form?
Molecules form based on their ELECTRON CONFIGURATION
To understand how molecules form we need to look at the valence electrons of each atom
Atoms want to have a FULL valence shell (the outermost ring)

5. Note: Group Number = Number of Valence Electrons
The atom will either LOSE or GAIN electron through chemical bonding in order to do this – the atom will do whatever is easier!
Note: Group Number = Number of Valence Electrons
Group # IA
IIA
IIIA
IVA VA
VIA
VIIA
VIIIA
Example Element Li Be B C N O F Ne
# Valence electrons 1 2 3 4 5 6 7 8
(Except He)
Tendency
Lose 1 e-
Lose 2 e-
Lose 3e-
Gain or Lose 4e-
Gain 3e-
Gain 2e-
Gain 1e-
None
(Stable)

6. Ions: When Atoms Aren’t Neutral
Because the number of protons is equal to the number of electrons, atoms are usually electrically neutral
When an atom loses or gains electrons when forming molecules, the atom will no longer be neutral
Atoms that LOSE ELECTRONS become POSITIVE
Atoms that GAIN ELECTRONS become NEGATIVE
An ion is an atom that has become electrically charged (positive or negative)