Chem 3.2

Define the terms first ionization energy and electronegativity

• First ionization energy of en element is the energy required to remove one mole of electrons from one mole of gaseous atoms.
• Electronegativity of an atom is its ability to attract electrons in a covalent bond

Describe and explain the trends in atomic radii, ionic radii, first ionization energies, electronegativities and melting points for the alkali metals (Li->Cs) and the halogens (F->I)

• The atomic radius increases down a group as the number of occupied electron shells (given by the period number) increases.
• The ionic radius increases down a group as the number of electron shells increases.
• Ionisation energies decrease down a group as the increased charge of the nucleus doesn't affect the outer electrons due to shielding and that the increased distance from the nucleus makes them easier to remove.
• Electronegativity decreases down a group as the bond electrons are furthest from the nucleus and so there is reduced attraction.
• Melting points decrease down the group for the alkali metals as metallic structures are held together by attractive forces between delocalized electrons and the positively charged ions. This attraction decreases with distance from the nucleus.
• Melting points increase down the group for halogens because the elements are held together by Van Der Waals forces and the increased number of electrons in the atom means the elements are held together more strongly.

Describe and explain the trends in atomic radii, ionic radii, first ionization energies and electronegativities for elements across period 3.

• Atomic radii decrease across a period as the occupied energy levels remain the same but as the charge of the nucleus increases there is no additional shielding attraction increases.
• Ionic radii have 4 trends: positive ions are smaller than their parent atoms; negative ions are larger than their parent atoms; ionic radii decrease from groups 1 to 4 for positive ions as nuclear charge increases; and ionic radii decrease from groups 4 to 7 for negative ions as the have the same electron configuration but greater nuclear charge.
• Electronegativity increases across a period due to an increase in nuclear charge resulting in an increased attraction between the nucleus and the bond electrons.

Compare the relative electronegativity values of two or more elements based on their positions in the periodic table.

• The most electronegative element is on the top right of the periodic table and the least electronegative element is on the bottom left.