Why do elements in the same group/family have similar properties?

Valence Electrons Elements in a group have similar properties –they have the same number of valence e- GroupValence Electrons 1A1 2A2 3A3 4A4 5A5 6A6 7A7

Representative Elements Elements in groups 1A through 8A

Hydrogen 1 valence e- Lavoisier: –Named b/c it forms water –Hydro (water) genes (to form) Cavendish –Flammable air –Easily reacts with air

Alkali Metals Group 1A Most reactive metals –Reactivity increases from the top to the bottom. –Many are kept under oil to prevent reacting with water or oxygen.

Alkali Metals One Valence e- –Forms atoms with +1 charge Soft Found in nature only in a compound –NaCl (Table salt) Form bases

Alkaline Earth Metals Group 2A 2 Valence Electrons (form 2+ ion) Reactivity shown by reactivity with water Harder: not as reactive as 1A –Hard water Form bases

Boron Family Group 3A 3 Valence electrons 1 metalloid (Boron) Five metals Aluminum is the most abundant metal in the Earth’s crust. –Usually combined with oxygen

Carbon Family Group 4A 4 Valence Electrons Wide range of properties –1 Nonmetal –2 Metalloids –3 Metals Most of the compounds in your body contain carbon.

Carbon cont Forms allotropes –Forms of an element with different structures and properties Silicon: 2 nd most abundant element in the earth’s crust after oxygen –(glass, sand, quartz)

Nitrogen Family Group 5A 5 Valence Electrons Very different properties Nitrogen: –78% of atmosphere –Forms explosive compounds –Fertilizer

Nitrogen Continued Phosphorus –2 allotropes

Oxygen Family Group 6A 6 valence e- Oxygen has 2 allotropes Sulfur has 10 allotropes

Halogens Group 7A 7 Valence electrons –Forms ions with -1 charge Known as “Salt Formers” Forms compounds with almost all metals 5 nonmetals 1 Unknown: (Astatine: radioactive no known uses)

Noble Gases Group 8A 8 Valence Electrons Un-reactive Odorless and colorless Used in light bulbs

Properties of Metal, Nonmetals, and Metalloids

Metals versus Nonmetals Metals tend to form cations. Nonmetals tend to form anions.

Metals Tend to be lustrous, malleable, ductile, and good conductors of heat and electricity.

Nonmetals Dull, brittle substances that are poor conductors of heat and electricity. Tend to gain electrons in reactions with metals to acquire noble gas configuration.

Metalloids Have some characteristics of metals, some of nonmetals. For instance, silicon looks shiny, but is brittle and fairly poor conductor.

Ionization: holding on to e- Electronegitivity: how much I want another e-

Answer: Because each group/ family has the same amount of valence electrons it’s useful in predicting atomic structure and, therefore, chemical properties.