Download Trends in the periodic table

Trends in the periodic table
Atomic radius
Atomic radii trends and explanations
• Atomic radius decreases across a period because
each successive element has one more proton in
its nucleus and one more electron is added to the
same valence shell.
• Therefore, each electron experiences a greater
effective nuclear charge so is attracted more
strongly to the nucleus resulting in a smaller
atomic radius.
• Atomic radius increases down a group because
as we progress down a group the valence
electrons are found in another shell much further
from the nucleus.
Ionic radius
Atomic vs ionic radius
• Cations: When cations form, all the valence
electrons are removed from the outer shell, so
the ions have one less shell than the atom.
This results in a smaller radius than the atom.
• Anions: When anions form, electrons are
added to the existing valence shell. Greater
repulsion between valence electrons results in
a larger radius than the atom.
Ionic radii trends and explanations
• Ionic radius increases down a group for the
same reason atomic radius increases.
• Ionic radius decreases across a period for the
cations for the same reason atomic radius
increases.
• However, here is a big jump in ionic radius
between cations and anions because the
anions have one more shell than the cations.
• The trend resumes for the anions.
1st ionization energy
1st ionization energy definition
• 1st ionization energy = amount of energy
needed to remove 1 mole of electrons from 1
mole of gaseous atoms (unit is kJ/mol).
• Endothermic process.
• Example equation:
Na(g)
Na+(g) + e-
Trends and anomalies
• 1st I.E increases across period because as effective
nuclear charge increases, valence electrons are held
more tightly, so more energy is needed to remove an
electron.
• Anomalies exist in trend due to more stable electron
configurations which require more energy to remove
electrons from half full or completely full subshells.
• 1st I.E increases down a group because valence
electrons are found in a shell much further from the
nucleus and are also shielded from the nucleus so are
not held as tightly and require less energy to remove.
Successive ionization energies
e.g sodium
Explanation of sodium successive I.E
Use the graph on the previous slide to explain
the successive ionization energies for sodium. In
your answer you should:
• Describe what 1st, 2nd, 3rd etc ionisation
energy means.
• Describe the overall trend.
• Explain the jumps in I.E by referring to which
shells and sub-shells electrons are being
removed from.
Electronegativity
• A measure of the attraction an atom has for electrons in a
bond.
• The four most electronegative elements are F, O, N and Cl.
• These elements have a high attraction for electrons in a
bond because their atomic radius is relatively small and
they have a high effective nuclear charge.
• Essentially F, O, N and Cl nuclei attract a pair of bonding
electrons more strongly than the nuclei of other elements
they are bonded to.
• Their nuclei are closer to the bonding electrons and they
have a higher effective nuclear charge to attract those
electrons.
Electronegativity and polarity of
bonds
• The difference in electronegativity helps to
determine whether a bond will be polar or
not.