Factors Affecting the Properties of Elements Answers
Sample Problems:
1. Which atom has the larger atomic radius, sodium or potassium? Explain your answer.
Potassium is larger since it has an additional filled energy lelvel (orbit).
2. Which atom is more metallic, magnesium or aluminum? Explain.
Magnesium is more metallic (i.e. more malleable, softer, better conductor) since it has a
weaker hold on its outer (valence) electrons. This is due to the fact that they both have 2
occupied energy levels (orbits), but magnesium has a weaker nuclear charge (fewer protons),
therefore it has a weaker hold on its outer electrons. This also makes magnesium more
reactive since metals usually lose electrons in reactions.
(Mg p12) 2,8,2 vs.
(Al p13) 2,8,3
3. Which atom is larger, chloride ion (Cl) or argon? Explain.
Note that a chloride ion and argon both have electron arrangements 2,8,8. (They are both
isoelectronic). However, argon has a greater nuclear charge pulling the outer electrons toward
the nucleus (electron orbits can be pulled closer to the nucleus). Therefore argon will be
smaller and
(Cl p17)2,8,8
vs
(Ar p18) 2,8,8
4. Which of these atoms would have the higher ionization energy, calcium or potassium?
Explain.
Calcium will have a higher IE since it has more protons. It will be more difficult to remove one
electron from this atom.
Trends in the Periodic Table Answers
1. a) How many valence electrons does nitrogen have?
5
b) Write the ionization equation for nitrogen.
N + 3eN3c) Based on the trends of the periodic table, what would you predict the charge would be on
a stable ion of arsenic? As3- since it is the same group (family) as nitrogen.
2. Consider the electron configuration (arrangement) of boron (2,3) and aluminum (2,8,3).
Why are they in the same group (family)?
Mendeleev arranged the elements into families based on their reactivity. Since they both
have 3 valence electrons they will have similar properties. For example, both will form
compounds with oxygen with the formula X2O3 (B2O3 and Al2O3).
3. a) Is a sodium atom larger or smaller than a magnesium atom?
Since Na has fewer protons, the valence electrons will be further from the nucleus.
b) Is a sodium atom larger or smaller than a sodium ion?
Sodium atom: (p11) 2,8,1
Sodium ion
(p11) 2,8
Since the atom has 3 filled energy levels, it will be much larger than the sodium ion.
4. a) Would you expect a neon atom to be larger or smaller than a sodium atom?
Nep10 2,8 compared with Nap11 2,8,1
The neon atom will be smaller since it has only 2 occupied energy levels.
b) Would you expect a neon atom to be larger or smaller than a sodium ion?
Since neon and a sodium ion are isoelectronic (they have the electron arrangement 2,8),
we must consider factor 2, the nuclear charge. The sodium ion has 11 protons and will
pull the electron orbits closer to the nucleus. Therefore the sodium ion is smaller and
the neon atom larger.
5. Explain why beryllium has a higher ionization energy than lithium.
Ionization energy always refers to how difficult it is to pull an electron off the atom,
forming a positive ion. So the reactions we are talking about are:
Bep4 2,2
Bep4 2,1 + 1e-
Lip32,1
Li+
+
1e-
Both are losing an electron from energy level (orbit) 2, so we ignore this factor.
Beryllium has a greater attraction for the electron due to its 4 protons compared to
lithium’s 3 protons. The greater the attraction, the higher the ionization energy.
Note that the lower the IE, the more reactive a metal is since it is easier for them to lose
electrons.
6. a) What is the most metallic element in the periodic table?
Francium (Fr)
b) What is the most nonmetallic element in the periodic table?
fluorine (F) or helium
(He) *fluorine is the most reactive non-metal.
7. Which of the following would have the smallest atomic radius?
O2-, F-, Ne, Na+, Mg2+
All these ions are isoelectronic (2,8). Since Mg has the most protons, it will be the smallest.
8. Consider the following electron configurations for neutral atoms:
i) 2,8,2
ii) 2,8,1
iii) 2,8
iv) 2,7
v) 2,5
Mg
Na
Ne
F
N
a) Which of these would you expect to have the lowest ionization energy? Na
b) Which do you expect to be a noble gas? Ne
c) List the five atoms in order of increasing ionization energy. Na < Mg < N < F <
Ne
9. Using their location of the periodic table, rank each set of elements in terms of increasing
atomic size (smallest to largest). Briefly explain the ranking in each case.
a) Cl < S < Mg
c) Ne < Ar <Xe
(as protons decrease, size increases)
(as # of orbits increase, size increases)
b) N < B < Al
d) Xe < Te < Rb
(N < B due to # protons; Al has more orbits) (as protons decrease, size increases)
10. Using their location of the periodic table, rank each set of elements in terms of decreasing
ionization energy (largest to smallest). Briefly explain the ranking in each case.
a) I < Br < Cl
c) K < Ca < Kr
(as # orbits increases, IE increases)
(as # protons increase, IE increases)
b) Ga < Ge < Se
(as # protons increases, IE increases)
d) Cs < Na < Li
(as # orbits decreases, IE increases)
11. Which element in each pair will have the lower electron affinity? Explain your response.
a) K or Ca
c) S or Se
(fewer protonsm weaker attraction
(more orbits, weaker attraction)
b) O or Li
(fewer protons weaker attraction)
d) Cs or F
(>>> orbits, much <<<< attraction)