Section 1.7: Periodic Trends in Atomic Properties
Mini Investigation: Organizing Aliens, page 38
A. Answers may vary. Sample answer: When I was arranging the cards, the first pattern I noticed
was the shape of the torso. The shapes were upright triangle, upside down triangle, rectangle,
circle, double circle. The next trait I noticed was the number and styles of the arms, then the
number and styles of the legs, then the number and styles of hair decorations.
B. Answers may vary. Sample answer: My alien table had three groups.
C. Answers may vary. Sample answer: My alien table had two periods.
D. Answers may vary. Sample answer: When the missing cards were included, there seem to be
six main groups based on torso style, leg style, hair style, face style, and number of arms.
Within each group, there were subgroups such as number of shapes and decoration for the torso,
number and style of legs, number of coifs per hair style, style of face, and style of arms.
E. Answers may vary. Sample answer: My table is analogous to the periodic table in that there
are several main groups with subgroups or periods. It is organized like the periodic table.
F. Answers may vary. Sample answer: A table with the headings “Solid,” “Liquid,” and “Gas” in
which the first 50 elements are sorted to show their state at standard temperature and pressure is
an example of a table in which items are organized by their properties.
Section 1.7 Questions, page 41
1. (a) The element actinium has the largest atomic radius in the halogen group.
(b) The element cesium has the largest atomic radius in the alkali metals group.
(c) The element radon has the largest atomic radius in the noble gases group.
2. F < C < Li < K < Rb < Cs
3. A magnesium atom has a radius of 150 pm. If the magnesium atom loses an electron, the
result is a magnesium cation. The force of attraction exerted by the nucleus on the each
remaining electron is greater, pulling each electron closer to the nucleus, so the radius is
decreased. If the magnesium atom gains an electron, the result is a magnesium anion. The force
of attraction exerted by the nucleus is less per electron, so the radius is increased.
4. Ionization energy is the quantity of energy required to remove an electron from an atom or ion
in the gaseous state, whereas electron affinity is the energy change that occurs when an electron
is added to a neutral atom in the gaseous state.
5. (a) Using Figure 2 in Section 1.7 and comparing the atomic radii:
(i) K > Ca (ii) Al > P (iii) I > F (iv) Ra > Li
(b) Using Figure 5 on in Section 1.7 and comparing the ionization energies:
(i) Ca > K (ii) P > Al (iii) F > I
(iv) Ionization energy decreases as you move down a group, so Ra will be less than Ba, but Ba is
less than Li, so Li has a higher ionization energy than Ra.
(c) Using Table 1 in Section 1.7 and comparing the electron affinities:
(i) Ca < K (ii) Al < P (iii) I < F
(iv) Electron affinity decreases as you move down a group, and it increases as you move across a
period. Ra is five rows below Li and one column over. As well, Ca has a much lower electron
affinity than K, so I predict that Ra will have a lower electron affinity than Li.
Copyright © 2011 Nelson Education Ltd.
Chapter 1: Atomic Structure and the Periodic Table
1.7-1
6. (a) The sulfide ion, S2–, is larger than the sulfur atom, S, because anions are always bigger
than their original neutral ions.
(b) The calcium ion, Ca2+, is smaller than the calcium atom, Ca, because cations are always
smaller than their original neutral atom.
(c) The fluoride ion, F–, is larger than the lithium ion, Li+. Students’ explanations may vary.
Sample explanation: From Figure 3 on page 37, it looks like the radius is about 100 pm larger
when the atom gains an electron and about 100 pm smaller when an electron is removed. The
atomic radius of Li is 167 pm, so the ionic radius of Li+ will be about 67 pm. The atomic radius
of F is 42 pm, so the ionic radius of F– will be about 142 pm.
(d) The bromine ion, Br–, is larger than the chloride ion, Cl–. Students’ explanations may vary.
Sample explanation: The bromine atom, B, is larger than the chlorine atom, Cl, so when each of
these two atoms gains an electron, bromine will likely remain larger.
7. There should be no significant differences between the first ionization energies of two isotopes
of a given element, because neutrons are uncharged particles.
8. (a) There are no anomalies for the periodic trend for atomic radius.
(b) For ionization energy in the second period, the ionization energy of B is less than that of Be.
This is unexpected and an anomaly for this trend. (This occurs because there is some stability
gained by the element when the first two electrons are placed in an energy level. This will be
examined in more detail in Grade 12U.)
9. (a) Answers may vary. Sample answer: I predict that francium will have an atomic radius of
310–330 pm. These values are determined by extending the trend for increasing atomic radius as
you descend down the alkali metal family.
(b) Answers may vary. Sample answer: I predict that ununseptium will have an atomic radius of
135–145 pm. These values are determined by extending the trend for increasing atomic radius as
you descend down the halogen family.
10. The sparks on the shiny silver rim of the plate indicate that the silver atoms are being ionized,
whereas the silicon and oxygen atoms are not being ionized. This is due to the fact that silver has
a lower ionization energy than silicon or oxygen. Microwaveable containers are usually made of
non-metallic materials because these materials have higher ionization energies and will not spark
in microwaves. Most pots and pans are metallic because metals conduct heat efficiently.
11. Answers will vary. Sample answers: Since Element 119 is an alkali metal, it will be soft,
silver-coloured, and a solid at room temperature. It should be extremely reactive with water and
air. It may have properties similar to those of francium or cesium.
12. Answers will vary. Sample answer: The atomic radii for the first three elements in Period 7
will most likely fall the in the following ranges: Fr (310–330 pm), Ra (280–300 pm), and
Ac (225–240 pm). These values are determined by extending the trend for increasing atomic
radius as you descend down the periodic table.
Copyright © 2011 Nelson Education Ltd.
Chapter 1: Atomic Structure and the Periodic Table
1.7-2