1. 5.3

2. Valence Electrons Elements in a group have similar properties because they have the same number of valence electrons. A valence electron is an electron that is in the highest occupied energy level of an atom.

3. Valence Electrons & Group Number When the A groups in the periodic table are numbered from 1 through 8, the group number matches the number of valence electrons in the electron configuration of an element in that group. Valence electrons play a key role in chemical reactions. Properties vary across a period because the number of valence electrons increases from left to right.

4. Alkali Metals Group 1A 1 Valence Electron Extremely Reactive and thus found only in nature as compounds

5. Alkaline Earth Metals Group 2A 2 Valence Electrons Highly Reactive Spinach plant Oyster shell with pearl Plaster cast

6. Boron Family Group 3A 3 Valence Electrons Ex: Aluminum = Most abundant metal in Earth’s Crust Lab Glass materials

7. Carbon Family Group 4A 4 Valence Electrons

8. Nitrogen Family Group 5A 5 Valence Electrons Elements with a wide range of physical properties Used a lot in fertilizer

9. Oxygen Family Group 6A 6 Valence Electrons Ex: Oxygen is the most abundant element in the Earth’s crust

10. Halogens Group 7A 7 Valence Electrons Found as gas, liquid or solid Despite these differences, chemical properties are the same

11. Noble Gases He has 2 valence electrons All the others have 8 Colorless, odorless and extremely unreactive = STABLE

12. Noble Gases But, when electric current passes through noble gases, they emit different colors. Helium emits pink, neon emits orange-red, argon emits lavender, krypton emits white, and xenon emits blue.

13. Electron Dot Diagram When is an atom unlikely to react? When the highest occupied energy level of an atom is filled with electrons, the atom is stable and not likely to react.

14. Electron Dot Diagram The chemical properties of an element depend on the number of valence electrons. An electron dot diagram is a model of an atom in which each dot represents a valence electron. The symbol in the center represents the nucleus and all the other electrons in the atom.

15. Electron Dot Diagram