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Each period number signifies the total number of electron shells an atom of the elements in that
period have, e.g. all elements in Period 3 (Na, Mg, Al, Si, P, S, etc.) have a total of 3 electron shells.
Similarly, all elements in Period 4 (K, Ca, Sc, Ti, V, Cr, etc.) have a total of 4 electron shells, and so
on.
The Trends in Groups of the Periodic Table
• In the periodic table, you need to know about: Group I, Group II, Group VII, Group VIII, as
well as the transition elements.
Group I (Alkali Metals):
The Group I elements include:
• Lithium (Li)
• Sodium (Na)
• Potassium (K)
• Rubidium (Rb)
• Caesium (Cs)
• Francium (Fr)
They are soft metals and have 1 electron in their outer-shell.
The Group I trends include:
• Melting/Boiling points decrease down the group.
• Density increases down the group.
• Reactivity increases down the group.
e.g. of reactions with water:
Observations of Group I metals reacting with water:
• The metal floats on the surface of the water and then dissolves.
• Effervescence/Bubbles of gas produced (produces popping sound with lighted splint).
• Colourless solution is formed which has a high pH value.
Group II (Alkaline Earth Metals):
The Group II elements include:
• Beryllium (Be)