Problem Set 5
Dr. Sparks, CH 301
1. Briefly describe the reasons for and effects of the following periodic trends across a row and down
a column: effective nuclear charge (Z
), atomic radii, ionic radii, ionization energy, electron affinity,
Across a period, the number of electrons and protons increase but the number of shielding electrons
(electrons in lower shells) remains the same, resulting in an increasing
effective nuclear charge
(ENC or Z
. Down a group the electrons occupy shells that are farther from the nucleus and these
electrons are more shielded, so ENC decreases.
decreases from left to right across a period because the ENC increases pulling
electrons closer to the nucleus.
increases down a group because of the increasing size
of orbitals with higher principal quantum numbers, and decreasing ENC.
decreases from left to right across a period. Elements experience a higher ENC and
electrons will be more tightly bound (closer to the nucleus).
In general, cations are smaller than
anions because they have lost electrons. Hence, they have usually lost a whole outer energy level and
they have more protons than electrons, allowing the protons to more effectively pull the electrons
closer in towards the nucleus.
increases as you go down a group because they have
more energy levels.
generally increases from left to right across a period due to increasing ENC. There
are some exceptions where atoms with half-filled shells are more stable than atoms with more
electrons, such as nitrogen, 1s
, versus oxygen, 1s
. Ionization energy decreases down
a group because electrons further away from the nucleus are more shielded.
generally increases (becomes more negative) across a period from left to right due
to increasing ENC, making it more attractive for an electron to join the atom. An element in Group
VIIA becomes more stable by gaining an electron and having a filled valence shell than does an
element in Group 1A. Down a group,
generally decreases. Any additional electrons
will be very shielded and not very attracted to the nucleus.
generally increases from left to right across a period. The atoms in groups on the
right side of the periodic table attract electrons to themselves in order to have a stable filled valence
orbital, like the noble gases. Down a group, ENC decreases, so atoms are less likely to attract
decreases down a group.
2. Arrange the following in terms of increasing effective nuclear charge