1. Electron Configuration and Bonding Section 15.1
Think about the electron configuration of elements in the same group (Alkali Metals – all end in s1)
Mendeleev recognized similar properties of elements in groups (Alkali Metals all react violently in water)

2. Example: Carbon’s electron configuration = 1s22s22p2
Valence electrons are the number of electrons in the highest occupied energy level
Example: Carbon’s electron configuration = 1s22s22p2
In the 2nd energy level, carbon has 4 electrons (2 in s and 2 in p)
Therefore, Carbon has 4 valence electrons

3. How about you try!
How many valence electrons do the following elements have?
Calcium 2
Nitrogen 5
Oxygen 6
Neon 8
Potassium 1

4. Electron Configurations for Ions
All atoms want to be stable – they want to be noble gases
in order to be stable, they want to have 8 valence electrons in their highest energy level
Ions will either gain or lose electrons to become more stable (like a noble gas)
Cation – ion that has a positive charge because it has lost electrons to become more stable
Anion – ion that has a negative charge because it has gained electrons to become more stable

5. Electron Configurations for Cations
Calcium atom = 1s22s22p63s2
Calcium has 2 valence electrons (2 electrons in the 3rd energy level)
To act like a noble gas, calcium can either lose 2 electrons or gain 6 electrons
Once calcium loses it’s 2 valence electrons, it becomes a cation with a +2 charge
Calcium ion = 1s22s22p6
Nuclear Symbol
Protons
Neutrons
Electrons
40Ca 20
Nuclear Symbol
Protons
Neutrons
Electrons
40Ca+2 20 18

6. Electron Configurations for Anions
Chlorine atom = 1s22s22p63s23p5
Chlorine has 7 valence electrons (2 electrons in the 3p sublevel and 5 electrons in the 3p sublevel)
To act like a noble gas, chlorine can either lose 7 electrons or gain 1 electron
Once chlorine gains 1 valence electron, it becomes an anion with a -1 charge
Chlorine ion = 1s22s22p63s23p6
Nuclear Symbol
Protons
Neutrons
Electrons
35Cl 17 18
Nuclear Symbol
Protons
Neutrons
Electrons
35Cl- 17 18

7. After reading Section 15.1, you should know:
How to determine the number of valence electrons the Representative Elements (s and p sublevels)
How to write the electron configuration for cations and anions