Chapter 16- The Periodic Table

• The periodic table is a list of elements arranged in order of increasing proton number.
• It is divided into horizontal rows called periods and vertical columns called groups.
• There are seven periods and eight groups. The eighth group is sometimes called the group O.
• Between group II and III, there is a block of metals called transition metals.

GENERAL TRENDS OF A PERIODIC TABLE

1. Group--- vertical column

2. Period--- horizontal row

3. There is a decrease in metallic properties across a period

4. Same group--- same valency/number of valence electrons

5. Same period--- same number of shells

6. Left to right--- gradual change from metals to non-metals

7. Group I to Group III--- lose electrons to form cations

8. Group V to Group VII--- gain electrons to form anions

9. Group IV--- can either gain or lose electrons

   10. Transition elements between Group II and III have variable valency
   11. Group VIII/O--- are stable and do not react
   12. Atomic size--- decreases across a period, increases down a group.

   The group number determines the number of valance electrons (and thus, valency) of the element while the period determines the number of electron shells in an atom of that element.

ALKALI METALS- GROUP I

Properties:

1. Soft, can be easily cut
2. Low melting and boiling points
3. Low densities, are light
4. Good thermal and electrical conductors
5. Highly reactive
6. React with cold water to form alkali and hydrogen: 2Na + 2H20 2NaOH + H20
7. React with halogens to form halides: 2Na + Cl2 2NaCl
8. Form ionic compounds
9. Are powerful reducing agents

Trends:

1. Increases down the group: density, reactivity, softness
2. Decreases down the group: Melting and boiling points

HALOGENS- GROUP VII

Properties:

1. Coloured
2. Low melting and boiling points
3. Highly reactive
4. Exist in diatomic state
5. Undergo displacement reactions: 2NaBr + Cl2 2NaCl + Br2
6. Are powerful oxidizing agents

Trends:

1. Increases down the group: Melting and boiling points, density, colour (darker)
2. Decreases down the group: Reactivity, state (gas to solid)

NOBLE GASES- GROUP O

Properties:

1. Low melting and boiling points
2. Colourless
3. Insoluble in water
4. Unreactive, provide inert situations

Trends:

1)       Increases down the group: Boiling point, mass

Uses:

1. Helium: for filling balloons and airships

2. Argon: for filling tungsten bulbs

3. Neon: used in lights and advertising signs

4. Xenon: used in vehicle headlamps

5. Argon: to provide inert atmosphere for processes like welding

6. Oxygen: welding, oxygen tents and tanks.