Exercise/atomic structure
Kit Sam Lam Bing Yim Secondary School
Atomic structure
Exercise
1.
Decide whether each of the following statements is true or false.
(a) All atoms contain protons, electrons and neutrons.
(
)
(b) One isotope of carbon has an atomic number of 6 and a mass number of 12. This
means that it has twice as many neutrons as protons.
(
)
(c) Electron shells are negatively charged.
(
)
(d) The second electron shell of an atom can hold a maximum of 8 electrons.
(
)
2.
(a) Complete the following table for atoms A to F. (The letters are not symbols of the
atoms)
Atom
Atomic
number
Mass
number
A
3
6
Number of
protons
neutrons
8
10
B
C
D
electrons
12
16
Electronic
configuration
2,8,1
16
E
16
F
27
8
2,8,3
(b) Name the atoms A, B and C.
(c) Which of the above atoms are isotopes?
3.
Give the names and symbols of the following elements (A to D) from the descriptions
given:
Element
Description
Name
A
Its atomic number is 7.
B
Its atom has 12 protons.
C
Its atom has 18 electrons.
D
The electronic configuration
of its atom is 2,8,8,1
P.1
Symbol
Exercise/atomic structure
4.
5.
6.
Draw electron diagrams for atoms of the following elements:
(a) Fluorine
(b) Calcium
(c) Phosphorus
(d) Sodium
An atom of element E contains 19 protons and 20 neutrons. The representation of this atom
is
A. 20
19 E
B.
20
39
E
C.
19
20
E
D.
39
19
E
Consider the information given in the table below:
Atom
Atomic number
Mass number
Number of neutrons
P
6
14
8
Q
7
14
7
R
6
13
7
S
8
18
10
T
10
20
10
Which of the following atoms are isotopes?
A. P and Q
B. P and R
C. R and S
D. S and T
7.
Element X occurs in nature as two isotopes, 63 X and 65 X. If the relative atomic mass of
X is 63.5. what is the relative abundance of the 63 X isotope?
A. 25%
B. 60%
C. 75%
D. 90%
P.2
Exercise/atomic structure
8.
Lithium occurs naturally in two isotopic forms. The relative abundance of each of these
isotopes is shown in the table below:
Isotope
6
Relative abundance (%)
7.4
Li
7
Li
92.6
(a) What is the meaning of the term 'isotope'?
(b) Calculate the relative atomic mass of lithium.
9.
Gallium occurs naturally in two isotopic forms, gallium-69 and gallium-71. The atomic
number of gallium is 31.
(a) How many neutrons are there in gallium-69?
(b) How many neutrons are there in gallium-71?
(c) The relative atomic mass of gallium is 69.8. Deduce the relative abundance of each
isotope in natural gallium.
10. Take the notation
39
19
X to represent an atom of the element X.
(a) State the number of protons, neutrons and electrons in an atom of X.
(b) Draw an electron diagram for an atom of element X.
(c) Name the element X.
P.3
Exercise/atomic structure
Kit Sam Lam Bing Yim Secondary School
Atomic structure
Suggested answers to exercise
1.
(a) False
The atom of hydrogen 11H does not contain neutron.
(b) False
The isotope has 6 protons and 6 neutrons.
(c) False
Electrons that occupy the shells are negatively charged.
(d) True
The maximum number of electrons the second electron shell can hold is 2(2)2, i.e. 8.
2.
(a)
Atome
Atomic
number
Mass
number
Number of
A
3
6
3
3
3
2,1
B
8
18
8
10
8
2.6
C
11
23
11
12
11
2,8,1
D
16
32
16
16
16
2,8,6
E
8
16
8
8
8
2,6
F
13
27
13
14
13
2,8,3
protons
neutrons electrons
Electronic
arrangement
(b) A - Lithium
B - Oxygen
C - Sodium
(c) B and E
3.
Element
Description
Name
Symbol
A
Its atomic number is 7.
Nitrogen
N
B
Its atom has 12 protons.
Magnesium
Mg
C
Its atom has 18 electrons.
Argon
Ar
D
The electronic arrangement of its atom is 2,8,8,1.
Potassium
K
P.4
Exercise/atomic structure
Kit Sam Lam Bing Yim Secondary School
Atomic structure
4.
(b)
(a)
(c)
(d)
5.
D
6.
B
7.
C
8.
(a) Atoms which have the same atomic number but different mass number are known as
isotopes.
(b) The relative atomic mass of lithium = 6×7.4% + 7×92.6%
= 6.926
9.
(a) 38
(b) 40
(c) Let the relative abundance of gallium-69 and gallium-71 be y% and (100-y)%
respectively.
69.8 = 69×y% + 71×(100-y)%
6980 = 69y + 7100 - 71y
2y = 120
y = 60
The relative abundance of gallium-69 is 60% and that of gallium-71 is 40%.
10. (a) Number of protons = 19
Number of neutrons = 20
Number of electrons = 19
(b)
(c) Potassium
P.5