Group 1 Metals with Water (DP IB Chemistry): Revision Note

Group 1 Metals with Water

• The Group 1 metals are called the alkali metals because they form alkaline solutions with high pH values when reacted with water

• Group 1 metals are lithium, sodium, potassium, rubidium, caesium and francium

• All Group 1 metal electron configurations end in ns¹:

  • Lithium = 2s¹

  • Potassium = 4s¹

Physical properties of the Group 1 metals

• The Group 1 metals:

  • Are soft and easy to cut, getting softer and denser as you move down the group

  • Have shiny silvery surfaces when freshly cut

  • Conduct heat and electricity

    • The conductivity is due to the delocalized electrons of the metallic bonding

  • Have low melting points

    • Melting point decreases down the group as atomic radius increases and metallic bonding gets weaker

  • Have low densities

Chemical properties of the Group 1 metals

• Group 1 metals react readily with oxygen and water vapour in air

  • This is why they are usually kept under oil to prevent unwanted reactions

• Group 1 metals react vigorously with water to form an alkaline metal hydroxide solution and hydrogen gas

group 1 metal + water → group 1 metal hydroxide + hydrogen

• Lithium

  • Lithium floats and reacts slowly

  • Bubbles of hydrogen gas are released

  • A clear, colourless solution of lithium hydroxide is formed

2Li (s) + 2H₂O (l) → 2LiOH (aq) + H₂ (g)

• Sodium

  • Sodium reacts more vigorously than lithium

  • Bubbles of hydrogen gas are produced

  • Enough heat is released to melt the sodium, which forms a small silvery ball that moves on the surface

  • A clear, colourless solution of sodium hydroxide is formed

2Na (s) + 2H₂O (l) → 2NaOH (aq) + H₂ (g)

• Potassium

  • Potassium reacts more violently than sodium

  • Hydrogen gas is released rapidly

  • The potassium melts into a shiny ball and dashes around on the surface

  • The reaction produces enough heat to ignite the hydrogen gas, producing a lilac flame

  • A clear, colourless solution of potassium hydroxide is formed 

2K (s) + 2H₂O (l) → 2KOH (aq) + H₂ (g)

Trend in reactivity down Group 1

• The reactivity of Group 1 metals increases down the group, because:

  • The atoms get larger as more electron shells are added

  • The outermost electron is further from the nucleus

  • There is more shielding from the inner electrons / shells

  • So, the attraction between the nucleus and the outermost electron becomes weaker

• Overall:

  • The outer electron is more easily lost, so the metals react more vigorously with water

  • This increase in reactivity reflects the increasing metallic character of the elements

    • Metallic character is how easily an atom loses electrons to form positive ions

Alkali metals with halogens

• All the alkali metals react vigorously with the halogens in Group 17

• The reaction results in an alkali metal halide salt

2Na (s) + Cl₂ (g) → 2NaCl (s)

• The reaction becomes increasingly vigorous going down Group 1 because:

  • The atoms of each element get larger going down the group

  • This means that the ns¹ electron gets further away from the nucleus and is shielded by more electron shells.

  • The further an electron is from the positive nucleus, the easier it can be lost in reactions