The Periodic Table of Elements - Elements in Group 1

The Periodic Table of Elements

the periodic table of elements

Related Content

group 1 elements

Group 1 Elements

The elements in Group 18 are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).  

Group 1 elements are:

  • also known as alkali metals (see why under chemical properties)
  • shiny when cut, but quickly tarnished upon exposure to air
  • soft and can be cut with a knife
  • are very reactive (they have to be stored in paraffin oil to prevent contact with oxygen and water in the air)

Group 1 is located at the left end of the periodic table. (refer to the periodic table above)

Reactivity of Group 1 Elements

atomic radius
Atomic radius increases down the group.

The reactivity of Group 1 elements increases down the group. This is because:

    • Group 1 elements react by donating 1 electron from the outermost shell (valence electron).
  • M → M+ + e
    • This makes alkali metals electropositive (they have a tendency to donate electrons).
    • The valence electron is held in place by the electrostatic force of attraction with the positively charged nucleus.
    • The atomic radius of elements increases down the group (refer to diagram).
    • The distance between the nucleus and the valence electron increases.
    • This causes the electrostatic force of attraction between the nucleus and the valence electron to weaken.
    • Therefore, it gets easier to donate the valence electron going down the group. (The electropositivity of alkali metals increases down the group)

Physical Properties of Group 1 Elements

metallic bond
Metallic bonding in alkali metals
  • Atomic radius increases down the group. This is due to an increase in the number of electron shells down the group.
  • Density increases down the group. As the atomic mass increases, the density increases (density = mass/volume). However, alkali metals have relatively low densities – lithium, sodium and potassium float on water.
  • Melting and boiling points of the elements decrease down the group.
    • Atoms of alkali metals are held together by metallic bonds (refer to diagram).
    • The distance between the positive nucleus (M+and the delocalised electron (blue circles) increases down the group.
    • This causes the strength of the electrostatic force of attraction between the positive nucleus and the delocalised electron to decrease down the group.
    • As a result, less heat energy is required to break the bonds between atoms.
    • Therefore, the melting and boiling points of the elements decrease down the group.
  • Since alkali metals are indeed metals, they are good conductors of electricity and heat.
  • They are soluble in water (see chemical properties).

Chemical Properties of Group 1 Elements

alkali metals react with oxygen, water and halogen

Alkali metals react with:

  • Oxygen
  • Water
  • Halogens

Reaction of Group 1 Elements with Oxygen

Reaction of Group 1 elements with oxygen
Reaction of Group 1 elements with oxygen

Alkali metals react with oxygen to form metal oxides.

Alkali metal + Oxygen → Metal oxide

4Li (s) + O2 (g) → 2Li2O (s)
Lithium + Oxygen → Lithium oxide

4Na (s) + O2 (g) → 2Na2O (s)
Sodium + Oxygen → Sodium oxide

4K (s) + O2 (g) → 2K2O (s)
Potassium + Oxygen → Potassium oxide

Observations (refer to diagram)

  • Lithium burns with a red flame in excess oxygen.
  • Sodium burns with a bright yellow flame in excess oxygen.
  • Potassium burns with a very bright lilac flame in excess oxygen.

All three reactions produce a white solid.

Metal oxides react with water to form an alkaline solution of metal hydroxide.

Metal oxide + Water → Metal hydroxide

Li2O (s) + H2O (l) → 2LiOH (aq)
Lithium oxide + Water → Lithium hydroxide

Na2O (s) + H2O (l) → 2NaOH (aq)
Sodium oxide + Water → Sodium hydroxide

K2O (s) + H2O (l) → 2KOH (aq)
Potassium oxide + Water → Potassium hydroxide

All three reactions produce colourless solutions that turn red litmus paper blue (alkaline solutions).

Reaction of Group 1 Elements with Water

Reaction of Group 1 elements with water
Reaction of Group 1 elements with water

Alkali metals react with water to form an alkaline solutions of metal hydroxides and hydrogen gas.

Alkali metal + Water → Metal hydroxide + Hydrogen gas

2Li (s) + 2H2O (l) → 2LiOH (aq) + H2 (g)
Lithium + Water  Lithium hydroxide + Hydrogen gas

2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g)
Sodium + Water  Sodium hydroxide + Hydrogen gas

2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g)
Potassium + Water  Potassium hydroxide + Hydrogen gas

Observations (refer to diagram)

  • Lithium moves slowly on the surface of the water.
  • Sodium moves rapidly on the surface of the water while burning with a yellow flame.
  • Potassium moves very rapidly on the surface of the water while burning with a lilac flame.

All three reactions produce colourless solutions that turn red litmus paper blue (alkaline solutions).

This is why Group 1 elements are called alkali metals.

TIME TO THINK

Why do lithium, sodium and potassium move on the surface of the water?

  • First, remember that all three alkali metals are less dense than water. This enables them to float on the surface of the water.

PHYSICS LINK – think about the conservation of momentum.

  • When hydrogen gas is produced, it creates momentum in the direction that it is released. 
  • By the law of conservation of momentum, the alkali metal must experience a momentum with equal magnitude in the opposite direction!
  • This is what causes the alkali metal to move on the surface of the water.
  • The more reactive the alkali metal, the higher the rate of hydrogen produced, the faster it moves on the surface of the water.

Reaction of Group 1 Elements with Halogens (Group 17 Elements)

Reaction of Group 1 elements with halogen
Reaction of Group 1 elements with halogen

Alkali metals react with halogens to form metal halides.

Alkali metal + Halogen → Metal halide

2Li (s) + Cl2 (g) → 2LiCl (s)
Lithium + Chlorine → Lithium chloride

2Na (s) + Cl2 (g) → 2NaCl (s)
Sodium + Chlorine → Sodium chloride

2K (s) + Cl2 (g) → 2KCl (s)
Potassium + Chlorine → Potassium chloride

This reaction also occurs in the same manner with bromine gas and iodine vapour.

Observations (refer to diagram)

  • Lithium burns with a red flame.
  • Sodium burns with a bright yellow flame.
  • Potassium burns with a very bright lilac flame.

All three reactions produce a white solid.

Practice Questions

Scroll to Top