Group 1 (Alkali Metals) (Edexcel GCSE Chemistry: Combined Science)

• Elements are arranged on the Periodic table in order of increasing atomic number where each element has one proton more than the element preceding it
• The table is arranged in vertical columns called groups numbered I – VIII and in rows called periods
• The period number tells you the number of electron shells an atom has:
  • E.g. elements in period 3 have 3 electron shells

• The group number tells you how many outer electrons each atom has:
  • E.g. group 6 elements have atoms with 6 electrons in the outermost shell

• The periodic table positions elements based on their properties which are linked to their electronic configurations
• Elements with the same number of electrons in the outer shell and hence similar chemical properties are placed in the same group
• This allows us to use the table to predict the properties of elements based on their position
• Groups 1, 7 and 0 are elements which have been classified into their respective groups using the periodic table

The periodic table is a road map of all the elements

• The group 1 metals are known as the alkali metals
  • They form alkaline solutions when they react with water

• The group 1 metals are lithium, sodium, potassium, rubidium, caesium and francium and they are found in the first column of the periodic table

The alkali metals lie on the far left of the periodic table, in the very first group

• The alkali metals share similar characteristic physical properties
• Some of these properties are:
  • They are all soft metals which can easily be cut with a knife
  • They have relatively low densities and low melting points
  • They are very reactive (they only need to lose one electron to become highly stable) 

The melting points of the alkali metals

Reaction with water

• The reaction of the group 1 metals with water provides evidence for categorising these elements into the same chemical family
• The general pattern shown is:

group 1 metal + water ⟶  metal hydroxide + hydrogen

2M (s) + 2H₂O (l) ⟶ 2MOH (aq) + H₂ (g)

      where M is Li, Na, K, Rb or Cs

• The hydroxides formed all have the same general formula and are colourless, aqueous solutions
• The metals are so named because they form alkalis in water

Sodium reacts vigorously with cold water

• Trends are patterns of behaviour in physical or chemical properties
• Following these trends seen in lithium, sodium and potassium, we can say that:
  • Rubidium, caesium and francium will react even more vigorously with air and water than the first three alkali metals

• Of the alkali metals, lithium is the least reactive (as it is at the top of group 1) and francium would be the most reactive (as it’s at the bottom of group 1)
• Using the information given in the trends we would predict that rubidium:
  • would be a soft grey solid
  • would appear shiny when freshly cut
  • would be more dense than potassium (> 0.86 g cm^-3)
  • would have a lower melting point than potassium (< 63.5 ^oC)