Download Chemistry Practice Problems

Chemistry Practice Problems
The Atom and its Electronic Structure
Subatomic Particles: Protons, Neutrons and Electrons and
the Nucleus
Questions:
1. Examine the following isotopic symbols and determine the number of protons,
neutrons and electrons in each species.
A.
B.
C.
32
16 S
44
2+
20 Ca
81
−
35 Br
2. Write the isotopic symbol and charge for each of the following species.
A.
An isotope with 18 protons, 18 neutrons and 18 electrons.
B.
An isotope with 16 protons, 18 neutrons and 18 electrons.
C.
An isotope with 56 protons, 82 neutrons and 54 electrons.
Answers:
1.
A. The atomic number, 16, provides the number of protons. There are 16
protons.
The mass number, 32, provides the number of protons plus neutrons (n). 16 +
n = 32. There are 16 neutrons.
The species is neutral (an atom). The number of electrons must equal the
number of protons. There are 16 electrons.
B. The atomic number, 20, provides the number of protons. There are 20
protons.
The mass number, 44, provides the number of protons plus neutrons (n). 20 +
n = 44. There are 24 neutrons.
The species is a +2 cation. There are two fewer electrons than protons. There
are 18 electrons.
Chemistry Practice Problems
C. The atomic number, 35, provides the number of protons. There are 35
protons.
The mass number, 81, provides the number of protons plus neutrons (n). 35 +
n = 81. There are 46 neutrons.
The species is a –1 anion. There is one more electron than the number of
protons. There are 36 electrons.
2.
A. The atomic number is 18. Examination of a periodic table shows that the
element with an atomic number of 18 is argon, Ar.
The mass number is the sum of the protons and neutrons. A = 18 + 18 = 36
The charge of the species is obtained by examination of the number of
protons and electrons. The two values are both 18. Therefore, the species is
neutral.
36
18 Ar
B. The atomic number is 16. Examination of a periodic table shows that the
element with an atomic number of 16 is sulfur, S.
The mass number is the sum of the protons and neutrons. A = 16 + 18 = 34
The charge of the species is obtained by examination of the number of
protons and electrons. There are two more electrons than there are protons.
Therefore, the overall charge is –2.
34 2 16 S
C. The atomic number is 56. Examination of a periodic table shows that the
element with an atomic number of 56 is barium, Ba.
The mass number is the sum of the protons and neutrons. A = 56 + 82 = 138
The charge of the species is obtained by examination of the number of
protons and electrons. There are two more protons than electrons. Therefore,
the overall charge is +2.
138
2+
56 Ba