Homework
• Pg 6 and 7
#5, 8, 10, 11, 12
• Write down questions 11 and 12 now
#11: Which has a higher ionization energy: K or Ca? Explain.
#12 Which has a higher ionization energy: P or S? Explain.
Tips for a Good Answer
• Did you state what the trend is? (increase or
decrease)
• Did you explain WHY?
• Just saying “because it increases to the left” is not
enough
• Did you use as many vocab words as possible? (see
page 4 on your packet)
• Take 5 minutes to look over your homework
Go over homework answers
1)
Why does atomic radius decrease as you move
across the periodic table?
As you move from left to right on the periodic table
the number of core electrons stays the same but the
number of protons increases. This increase in
effective nuclear charge pulls the valence electrons
closer to the nucleus, resulting in a smaller radius.
2)
How are the trends of atomic radius and ionization
energy related? Explain in both groups and periods.
These trends are inverses of each other. As the size of the
atom increases, the ionization energy (energy required to
remove the electron) decreases because the electron
being removed is farther from the nucleus in a larger
atom. Less energy is required to remove an electron
further from the nucleus. [AR increases down a group
while IE decreases; AR decreases across a period while IE
increases.]
3)
What’s the difference between
electronegativity and ionization energy?
Electronegativity is related to the pull of a nucleus on
an electron being shared in a bond. Ionization energy
is the energy required to remove an electron from an
unbonded atom. Electronegativity is a ranking and
has no units. Ionization energy is an amount of
energy and has units such as kilojoules.
4)
What does it mean to be isoelectronic? Identify
the largest ion and smallest ion of the group: Se2-, Br1-, Kr,
Rb1+, Sr2+. Explain why.
Isoelectronic means a group of atoms/ions having the
same number of electrons. All of the atoms in this group
have 36 electrons; each atom/ion has the same number
of core electrons and the same amount of electron
shielding. What they don’t have in common (and what
accounts for the difference in size) is the number of
protons. The atom/ion with the most protons will be
smallest (Sr2+) while the atom/ion with the lowest
number of protons will be largest (Se2-).
5)
What does the octet rule have to do with the
periodic trends?
A trend like ionization energy is very closely related
to the octet rule. The halogens are the smallest of
atoms and the closest to the having a full octet. Since
gaining an electron would give these atoms a full
octet, the amount of energy required to remove an
electron (IE) would be very high. When determining
the charge an atom will have (as in number 4), the
number of electrons gained or lost is the number
required to have a full octet of electrons.
6)
The first ionization energy of beryllium is 9.322
eV, the second ionization energy is 18.211 eV, and
the third ionization energy is 153.893 eV. Explain
why the third ionization energy of beryllium so much
higher than the first two.
[eV is a electronVolt and is a unit of energy] When Be
has lost two electrons to become Be2+ it has the
electron configuration of a noble gas (He). This
electron configuration is very stable, so a much larger
amount of energy is required to remove the third
electron.
On your color coded periodic
table
• Using a marker, draw an arrow indicating the
direction that atomic radius increases across a
period and in a group
• Using a different colored marker, draw an arrow
indicating the direction that ionization energy
increases across a period and in a group
• Using a different colored marker, draw an arrow
indicating the direction that electronegativity
increases across a period and in a group
Mendeleev and the PT
Metals, Nonmetals, Metalloids
• Packet pg 3
Practice Quiz
• 15 minutes
• Get a sheet of paper out
• You need a writing utensil
1.Rank in order of increasing size:
iodine, selenium, krypton, and
bromide? Explain.
2.Explain the trend for atomic
radius down a group.
3.Explain the trend for ionization
energy across a row.
1
Kr, Br-, Se, I (1 point)
Kr, Br-, and Se are all on the same period. Since Kr
and Br- are isoelectronic, Kr is smaller because it has
more protons to pull in the electrons. Se is the
largest in that period because it has the lowest
effective nuclear charge (less protons). Iodine is the
largest because it has an additional energy level
(more core electrons, more electrons shielding). (2
points)
2
(1 point per underlined word= 4 points total) Atoms
get larger as you descend a column. Adding one
additional shell (energy level) increases the amount
of electron shielding within the atom. The additional
core electrons make the valence electrons farther
from the nucleus.
3
(1 point per underlined word= 5 points total) As you
move across a row, electrons are being added to the
same shell, so there is no change in the amount of
electron shielding, but the effective nuclear charge
also increases, pulling valence electrons closer to the
nucleus. Removing an electron closer to the nucleus
requires more energy.
How did you do?
• Test Monday/Tuesday
• Are you ready?