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-

Group Valence Electrons

1A 1

2A 2

3A 3

4A 4

5A 5

6A 6

7A 7

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: 2nd 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.