Chemistry Unit 1

Unit 1.6: The periodic table

The periodic table

Chemists classify elements according to their position in the periodic table. Periodicity is the term used to describe the repeating pattern of properties observed within the periodic table.

Electronegativity – decreases down the group as there is more electron shielding

Ionisation energy – decreases down the group (electron shielding and outer electron is further from the nucleus.

Group 1

Melting and boiling point decreases down the group due to metallic bonding: electrons are more widely spread out.

Reactivity increases down the group.

Group salts = insoluble

Ionization energy decreases down the group.

Electronegativity decreases down the group

 

Group 2

React with water to produce hydroxides.

They are bases.

Increase in reactivity down the group.

Increase in pH down the group.

Solubility decreases down the group.

All Group 2 carbonates are insoluble.

 

Barium sulphate (white precipitate)

Magnesium hydroxide (white precipitate)

Calcium carbonate (white precipitate)

 

 

Period 3 Elements

All trends listed here are for progression from left to right of the periodic table:

·         Reactions with water Na and Mg, Reactivity decreases

·         The elements progress from metals to non-metals.

·         Acidity increases

Halogens

Decrease in reactivity down the group.

Increase in boiling point down the group.

Decrease in electronegativity down the group.

Fluorine is the best oxidizer. Florine is a gas, iodine is a solid.

 

Uses of transition metals

V₂O₅ is used as a catalyst in the Contact Process (manufacture of sulfuric acid).

Cis-platin (a platinum complex) is a very effective anti-cancer drug.

Fe²⁺ is an important part of haemoglobin.

Ag(NH₃)₂⁺ is Tollen’s reagent (test for aldehydes).

Ag(S₂O₃)₂^3- is formed during photographic processing.

Ag(CN)₂^- is used in electroplating.

 

Group VII, the Halogens

Decrease in reactivity down the group.

Increase in boiling point down the group.

Decrease in electronegativity down the group.

Fluorine is the best oxidizer.

Florine is a gas, iodine is a solid.

 

Halogen

In pure form

In non-polar solvents

In water

Fluorine

Pale yellow gas

-

(Reacts with solvents)

-

(Reacts with water)

Chlorine

Pale greengas

Pale green solution

 

Pale green solution

Bromine

Dark red liquid

Orange solution

 

Orange solution

Iodine

Grey solid

Purple solution

-(Insoluble)

but forms a brown solution if excess KI is present

(Insoluble)

 

The halogens are usually used in aqueous solution. Although iodine is insoluble in water, it…