TRENDS IN THE PERIODIC TABLE
ATOMIC SIZE
1) a) What kind of force exists between the particles in the energy levels and the
particles in the nucleus?
2) As you move across a period in the periodic table:
a) what happens to the nuclear charge?
b) what happens to the electron shielding?
c) What happens to the atomic radius of an atom as you move across the
period? Why? (use the proper terminology)
3) As you move down a group in the periodic table:
a) what happens to the effective nuclear charge?
b) what happens to the electron shielding?
c) What happens to the atomic radius of an atom as you move down a group?
Why? (use the proper terminology) (2 I)
4) For each pair of elements listed below, which has the smaller atomic radius? Explain
your answer using the correct terminology (3 A)
a) Zn and Ca
b) Kr and Ar
c) Al and F
IONIC RADIUS
Ions are formed when elements react. A cation is formed when an atom (usually a metal)
loses an electron and forms a positive ion. An anion is formed when an atom (usually a nonmetal) gains an electron and forms a negative ion.
5) When a cation is formed (use sodium and the sodium cation as your example).
a) What happens to the attractive force experienced by the electrons in the cation
as compare to the force experienced by the electrons in the neutral atom?
Explain.
b) Will the cation be smaller or larger than the neutral atom? Why?
6) When an anion is formed (use fluorine and the fluoride ion as your example)
a) What happens to the attractive force experienced by the electrons in the anion
as compare to the force experienced by the electrons in the neutral atom?
Explain.
b) Will the anion be smaller or larger than the neutral atom? Why?
7) In the following pairs of ions/atoms, determine which one will be larger and explain
your answer (3 A)
a) N3- and O2-
b) Al3+ and Na+
c) Ne and F-
IONIZATION ENERGY
Ionization energy is the energy required to remove an electron from an atom. Often the effect
of ionization energy is represented with the equation:
X(g) + energy  X+(g) + eIn this equation the energy is being added to a gaseous neutral atom and a cation is
produced with the release of the electron. The stronger the attraction of the charge in the
nucleus for the valence electrons, the larger the ionization energy will have to be. When
answering these questions use the correct terminology in your explanations.
8) Will the ionization energy of neutral atoms increase or decrease from left to right in a
period on the periodic table. Explain your answer. (2 I)
9) Will the ionization energy of neutral atoms increase or decrease down a group in the
periodic table? Explain your answer. (2 I)
10) Explain why hydrogen has a first ionization energy of 1310 kJ/mol which is more than
twice the first ionization of lithium even though hydrogen only has one proton in its
nucleus (on p. 54 of your text you can see that in all of the other groups the element at
the top of the group does not have twice the ionization energy of the next element
down, only hydrogen does). (2 I)
11) Will the second ionization energy (the energy required to remove the second valence
electron) be greater or smaller than the first? Explain (2I)
12) In the following pairs identify which element will have the greater first ionization
energy. Explain your answer. (2 A)
a) I and F
b) Si and Na
13) Potassium will have a relatively low first ionization energy but its second ionization
energy is much higher than the second ionization energy of calcium. Explain this
observation. (2 A)
ELECTRON AFFINITY
Electron affinity is a measure of the energy released when an electron is added to the outer
energy level of a neutral atom to form a negative ion. The effect of electron affinity is often
represented with the equation:
X(g) + e-  X-(g) + energy
You might be asking yourself: “Why is energy RELEASED when an electron is added?”. If we
consider the Law of Conservation of Energy, we know that energy cannot be created or
destroyed. Consequently, if energy is required to remove an electron from an atom (as we
saw with ionization energy), energy must be released when an electron is added to an atom.
The electron that is captured by the atom is travelling around the atom at approximately the
speed of light. When it is captured by the atom, its kinetic energy is reduced and converted to
potential energy (in the form of the attraction between the electron and the protons in
nucleus). Some energy is also released, and this is the electron affinity. The greater the
electron affinity, the more stable the resulting anion formed. For example sodium is a metal
which becomes more stable if it loses an electron, therefore if we try to add an electron we
are going to discover that a very small amount of energy is release because sodium is less
stable if an electron is captured. However, if fluorine captures an electron, we would expect a
very large amount of electron affinity because the fluoride anion is more stable than neutral
fluorine.
14) Will the electron affinity increases or decreases across a period in the periodic table?
Explain your answer. (2 I)
15) Will the electron affinity increase or decrease down a group? Explain your answer. (2
I)
16) Which element in each of the following pairs will have the lower electron affinity.
Explain your answer. (2 A)
a) O or Li
b) Cs or S
ELECTRONEGATIVITY
The electronegativity of an atom is a measure of the atom’s ability to attract electrons in a
chemical bond. The most electronegative element is fluorine because it has the least
shielding, the greatest effective nuclear charge and the smallest atomic radius.
17) Do you think the electronegativity of neutral atoms will increase or decrease from left
to right in a period on the periodic table. Explain your answer. (2 I)
18) Will the electronegativity of neutral atoms increase or decrease down a group in the
periodic table? Explain your answer. (2 I)
19) How would you characterize the electronegativity of the noble gases? Explain your
answer. (1 K/U)
20) Arrange the following elements in increasing order of electronegativity. Explain your
answer. (2 A)
a) Li, Br, Zn, La, Si
b) P, Ga, Cl, Y, Cs