Electron Configuration and BondingSection 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)

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

How about you try!

How many valence electrons do the following elements have?

Calcium 2

Nitrogen 5

Oxygen 6

Neon 8

Potassium 1

Electron Configurations for IonsAll atoms want to be stable – they want to be

noble gasesin order to be stable, they want to have 8 valence

electrons in their highest energy levelIons 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

Electron Configurations for CationsCalcium 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+2 20 20 18

Nuclear Symbol

Protons Neutrons

Electrons

40Ca 20 20 20

Electron Configurations for AnionsChlorine 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 17

Nuclear Symbol

Protons Neutrons

Electrons

35Cl- 17 18 18

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