SKC year 13 Chemistry: June 2010

Trends on the periodic table are as follows.

1. Atomic radii: (half the distance between adjacent atoms nuclei)
Decreases across the table and down the groups.
Across the table: electron shells remain the same, but number of protons is increasing = protons have a greater pull of outer electrons.
Down the group: electron shells are increasing so there is electron shielding from the pull of the protons.

2. Ionic radii: (half the distance between adjacent ions nuclei)
Cations are smaller than their atoms as they have lost electrons.
Anions are larger than their atoms as they have gained electrons.

3. Electronegativity: (A measure of the ability of an atom to attract towards itself an electron stared in a chemical bond)
Increases across the period and decreases down the group.
Across the table: Across the table: electron shells remain the same, but number of protons is increasing = protons have a greater pull on bonded electrons
Down the group: electron shells are increasing so there is electron shielding from the pull of the protons.

4. First ionization energy: (energy needed to remove the least tightly held electron form an atom in gaseous state)
Increases across the period and decreases down the group.
Across the table: Across the table: electron shells remain the same, but number of protons is increasing = protons have a greater pull on valence electrons, so are harder to remove.
Down the group: electron shells are increasing so there is electron shielding from the pull of the protons make the valence electron easier to remove.