Valence Electrons
the electrons in an atom's outermost orbital
Valence electrons ...
• have the highest energy
• are held loosely
• determine how the atom will bond
Nitrogen
How many valence e ­ does Nitrogen have?
5
Valence Electrons and the Periodic Table
• In groups 1 & 2, the number of valence e­ is equal to the group number
ve ­
7 ve ­
6 ve ­
5 ve ­
4 ve ­
3 2 ve ­
8 1 ve ­
ve ­
• In groups 13­18, the number of valence e­ is equal to the group number ­ 10
all atoms strive to have their outer orbital full.
• For most atoms, their goal is to have 8 valence electrons­ filling their outer orbital
• Hydrogen and Helium are exceptions.
They only need 2 valence electrons to fill their outer orbital.
• Atoms will reach their goal by bonding with other atoms!
Drawing orbital diagrams
1. Draw the nucleus
2. Calculate the number of TOTAL electrons..
3. Place the first 2 electrons in the closest orbital
4. Place 8 electrons in every orbital after.
Example:
18 p+
18 e-
18
Ar
Argon
39.948
Magnesium
Using your periodic table, place the electrons in the correct orbitals.
How many ve­ does Mg have?
Drawing Electron Dot Diagrams
1. Draw the element symbol
2. Determine the number of VALENCE e­ in the atom. 3. Starting on the right side, place a dot representing a ve­. 4. Continue until all ve­ are represented.
All sides must have 1 dot before pairs can be made!
7 ve­
5 ve­
N
Cl
Try this...
Draw electron dot diagrams for each
Na Cl
Li F
Ca O
Stability of Elements
• The most stable elements have a full outermost orbital (8ve­)
Octet Rule ­­> elements tend to form bonds in a way that gives them 8 valence electrons.
Sodium
Chlorine