Topic 3 study sheet
1) Atomic radius:
a. Atomic Radius increases down a group; this is because the atoms down a
group have increasingly more electron shells- so the shielding effect
increases- meaning that there is more repulsion between the nucleus and
the valence electrons.
b. Atomic radius decreases across a period; this is because the nuclear
charge increases across the period with no significant change in
shielding- so the shielding effect decreases- meaning that there is less
repulsion between the nucleus and the valence electrons.
2) Ionic radius:
a. The ionic radii of positive ions are smaller than their atomic radii;
this is because a main energy level is lost- with the loss of an
electron- becoming closer to the nucleus. Other than that, the effective
nuclear charge of the ion is greater, meaning greater attraction between
the nucleus and the valence electrons.
i. The higher the positive charge, the smaller the ion.
b. The ionic radii of negative ions are greater than their atomic radii;
this is because the electrons are added to the same valence energy
level. Other than the effective nuclear charge of the ion is less,
meaning less attraction between the nucleus and the valence electrons.
i. The higher the negative charge, bigger the ion.
3) Ionization energy: The energy required to remove each atom in one mole of
gaseous atoms under standard conditions.
a. Down a group, the first ionization energy decreases; this is because the
number of main energy levels increases, the distance between the valence
electron and the nucleus increases, the valence electron is less
strongly attracted to it, making it easier to remove from the atom
b. Across a period, the first ionization energy increases; this is because
of an increase in nuclear charge across the period, the number of main
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energy levels stays the same, the distance between the nucleus and the
valence electron stays the same, the nuclear charge increases meaning
that the attraction between the valence electron and the nucleus is
greater so more energy is required to remove the valence electron.
o Exceptions:
o Groups 2 and 13: The valence electrons in group 2 are in sub energy
level s, while in group three the valence electrons are in sub
energy level p. Sub energy level p has higher energy than sub
energy level s meaning that it is farther away from the nucleus,
therefore less energy is required to remove the electron in it.
Other than that, sub energy level s in group two is relatively
stable and removing an electron disturbs this stability, which
requires more energy.
o Groups 15 and 16: Group 15 valence electron is removed from half a
full sub energy level which is relatively stable, removing an
electron disturbs this stability, which requires more energy. In
group 16, the valence electron is removed from a full p orbital and
the electron-electron repulsion between the two electrons in the
orbital reduces the amount of energy required to remove the valence
electron
4) Electron affinity: The enthalpy (energy) change when one electron is added
to each atom in one mole of gaseous state under standard conditions.
a. Going down group 17, the electron affinity decreases; this is because
the electron is added to a shell farther away from the nucleus, so the
attraction force between the nucleus and the added electron decreases
which means lower electron affinity (less exothermic as it releases less
energy).
o F is an exception because it is smaller than Cl, so the electrons
are closer together and there is more repulsion which reduces the
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1) Atomic radius:
a. Atomic Radius increases down a group; this is because the atoms down a
group have increasingly more electron shells- so the shielding effect
increases- meaning that there is more repulsion between the nucleus and
the valence electrons.
b. Atomic radius decreases across a period; this is because the nuclear
charge increases across the period with no significant change in
shielding- so the shielding effect decreases- meaning that there is less
repulsion between the nucleus and the valence electrons.
2) Ionic radius:
a. The ionic radii of positive ions are smaller than their atomic radii;
this is because a main energy level is lost- with the loss of an
electron- becoming closer to the nucleus. Other than that, the effective
nuclear charge of the ion is greater, meaning greater attraction between
the nucleus and the valence electrons.
i. The higher the positive charge, the smaller the ion.
b. The ionic radii of negative ions are greater than their atomic radii;
this is because the electrons are added to the same valence energy
level. Other than the effective nuclear charge of the ion is less,
meaning less attraction between the nucleus and the valence electrons.
i. The higher the negative charge, bigger the ion.
3) Ionization energy: The energy required to remove each atom in one mole of
gaseous atoms under standard conditions.
a. Down a group, the first ionization energy decreases; this is because the
number of main energy levels increases, the distance between the valence
electron and the nucleus increases, the valence electron is less
strongly attracted to it, making it easier to remove from the atom
b. Across a period, the first ionization energy increases; this is because
of an increase in nuclear charge across the period, the number of main
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, Topic 3 study sheet
energy levels stays the same, the distance between the nucleus and the
valence electron stays the same, the nuclear charge increases meaning
that the attraction between the valence electron and the nucleus is
greater so more energy is required to remove the valence electron.
o Exceptions:
o Groups 2 and 13: The valence electrons in group 2 are in sub energy
level s, while in group three the valence electrons are in sub
energy level p. Sub energy level p has higher energy than sub
energy level s meaning that it is farther away from the nucleus,
therefore less energy is required to remove the electron in it.
Other than that, sub energy level s in group two is relatively
stable and removing an electron disturbs this stability, which
requires more energy.
o Groups 15 and 16: Group 15 valence electron is removed from half a
full sub energy level which is relatively stable, removing an
electron disturbs this stability, which requires more energy. In
group 16, the valence electron is removed from a full p orbital and
the electron-electron repulsion between the two electrons in the
orbital reduces the amount of energy required to remove the valence
electron
4) Electron affinity: The enthalpy (energy) change when one electron is added
to each atom in one mole of gaseous state under standard conditions.
a. Going down group 17, the electron affinity decreases; this is because
the electron is added to a shell farther away from the nucleus, so the
attraction force between the nucleus and the added electron decreases
which means lower electron affinity (less exothermic as it releases less
energy).
o F is an exception because it is smaller than Cl, so the electrons
are closer together and there is more repulsion which reduces the
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