Module 3 Practice

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Exercise \(\PageIndex{1}\)

For each isotope shown, give the number of protons, neutrons, and electrons.

a) ¹⁹₉F^1–

b) ⁵²₂₄Cr³⁺

c) ³¹₁₅P^3–

Answer a: 9 protons, 10 neutrons, 10 electrons
Answer b: 24 protons, 28 neutrons, 21 electrons
Answer c: 15 protons, 16 neutrons, 18 electrons

Exercise \(\PageIndex{1}\)

Given the number of protons, neutrons, and electrons, what would be the mass number and the charge number of each isotope? What would be the atomic number? The identity of the element?

d) 14 protons, 15 neutrons, 14 electrons

e) 3 protons, 4 neutrons, 2 electrons

f) 30 protons, 36 neutrons, 28 electrons

Answer d: Mass number is 29, charge is 0. Atomic number is 14, identity is silicon (Si).
Answer e: Mass number is 7, charge is +1. Atomic number is 3, identity is lithium (Li).
Answer f: Mass number is 66, charge is +2. Atomic number is 30, identity is zinc (Zn).

Exercise \(\PageIndex{1}\)

For each element shown, tell what charge it has when it forms an ion.

g) S

h) Ag

i) Ca

Answer g: –2
Answer h: +1
Answer i: +2

Exercise \(\PageIndex{1}\)

Give the electron configuration for each of the following atoms.

j) Mg

k) Mn

l) Sr

Answer j: 1s² 2s² 2p⁶ 3s² (total of 12 electrons)
Answer k: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁵ (total of 25 electrons)
Answer l: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² (total of 38 electrons)

Exercise \(\PageIndex{1}\)

Give the electron configuration for each of the following ions.

m) N^3–

n) S^2–

o) Rb¹⁺

Answer m: 1s² 2s² 2p⁶ (total of 10 electrons)
Answer n: 1s² 2s² 2p⁶ 3s² 3p⁶ (total of 18 electrons)
Answer o: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ (total of 36 electrons)

Exercise \(\PageIndex{1}\)

K Ca

Rb Sr

Out of the four elements listed above, choose the one that has

j) the largest radius

k) the least ionization energy

l) the most metallic character

Answer j: Rb
Answer k: Rb
Answer l: Rb

Exercise \(\PageIndex{1}\)

The element chlorine is found in nature as a mixture of ³⁵Cl and ³⁷Cl. Given that the average atomic mass of chlorine is 35.45 amu, which isotope is more abundant?

Answer: ³⁵Cl is more abundant. Since the average mass is closer to 35 amu, you have more of the isotope with a mass of 35 amu than you do of the isotope with a mass of 37 amu.

Exercise \(\PageIndex{1}\)

If there were chemists on another planet, their periodic table might be different because the elements might have different "natural" abundances. If on the other planet, the element sulfur had the following natural abundances, calculate the average atomic mass that the chemists on that planet would use.

68.44 % is ³²S with mass of 31.9721 amu

23.24 % is ³³S with mass of 32.9715 amu

8.32 % is ³⁴S with mass of 33.9679 amu

Answer

Add up (uncertain digits are underlined):

21.8817amu

7.6626 amu

2.8261 amu

Total is 32.3704 amu which rounds to 32.37 amu