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)

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

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 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

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

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

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