Atoms and Elements Assignment 1
Complete the following questions on a piece of loose leaf. Write neat and clear and when
appropriate box or circle your final answer.
1. Define each of the following:
a) Atomic number: The atomic number is the number of protons in the nucleus of an
atom.
b) Mass number: The mass of an atom that is equal to the number of protons and the
number of neutrons in the nucleus of the atom.
c) Isotope: Isotopes are atoms of the same element (THE SAME ATOMIC NUMBER
AND THE SAME NUMBER OF PROTONS), but with different number of neutrons (and
as a result, a different mass number).
d) Ion: Positively or negatively charged atoms.
2. Identify the elements according to the following atomic numbers:
3 - lithium
43 - technetium
19- potassium
30- zinc
3. An atom has 14 protons and 13 neutrons. What is its mass number?
Atom – Silicon
Mass # - 28.09 OR 28
4. An atom has 15 protons and a mass number of 31.
a) What is its atomic number?
15
b) How many electrons does it have?
15
5. An atom of aluminum has 14 neutrons and a mass number of 27. How many protons and
electrons does it have?
Protons – 13
Electrons - 13
6. Redraw and fill in the following chart:
7. Does K or Na have more neutrons? Explain.
Na has 11 protons and K has 19 protons. This means we would expect K to have more neutrons
because the neutrons are required to hold more protons together in the nucleus. And when we
calculate the number of neutrons, K = 20 and Na = 12 as expected.
8. a) Calculate the average atomic mass of Lithium from the following data. Then write the symbolic
representation for each isotope of Lithium. Show your work.
Isotope
Atomic mass (g/mol)
Lithium – 6
6.015
Lithium – 7
6.938
ANSWER: 6.85amu or 6.85g/mol
ANSWER: 63Li 73Li
Abundance (%)
9.68
90.32
NOTICE…
This column add up
to 100 %!!
c) Calculate the average atomic mass of Magnesium from the following data. Then write the
symbolic representation for each isotope of Magnesium.
Isotope
Atomic mass (g/mol)
Abundance
Mg – 24
23.98
0.7860
Mg – 25
24.99
0.1011
Mg – 26
25.98
0.1129
ANSWER: 24.308amu or 24.308 g/mol
ANSWER: 2412Mg 2512Mg 2612Mg
NOTICE…
This column add up
to 1!!
9. a) The element Strontium has four naturally occurring isotopes with atomic masses of 83.91amu,
85.91amu, 86.91amu, and 87.91amu respectively. If 8438Sr represents the first isotope, give the
symbolic representation for the other three isotopes.
ANSWER: 8638Sr 8738Sr 8838Sr
b) If the abundances of the four Strontium isotopes are 27.1%, 23.7%, 24.60% and 22.8%
respectively, calculate the average atomic mass for Strontium.
ANSWER: 84.524amu or 84.524 g/mol
10. You isolated a monatomic ion through experimentation; determine the identity of the ion given the
following information:
a) The atom has 20 protons and a plus two charge, what is the identity of the ion?
Ca2+
b) The atom has 18 electrons and a plus three charge, what is the identity of the ion?
Sc3+
c) The atom has 54 electrons and a negative two charge, what is the identity of the ion?
Te2d) The atom has 78 protons and a plus two charge, what is the identity of the ion?
Pt2+
e) The atom has 10 electrons and a negative two charge, what is the identity of the ion?
O2-
11. Copy and complete the chart:
Symbol
Atomic #
Mass #
Sn
50
110
In
116
49
207
Pb
82
47
Ag
107
Fr
87
223
Cd
48
110
12. Copy and complete the chart:
Anion, cation, or
element
2Te
anion
Ianion
Pb
element
K+
cation
Ne
element
4+
Sn
cation
Ar
element
Pb2+
Cation
Al3+
cation
2O
anion
Br anion
# of protons
50
49
82
47
87
48
# of neutrons
60
67
125
60
136
62
# of electrons
50
49
82
47
87
48
# of protons
# of electrons
52
53
82
19
10
50
18
82
13
8
35
54
54
82
18
10
46
18
80
10
10
36
13. Draw Bohr diagrams and Lewis structures for the following atoms and ions: Si, S2-, Be2+, P,
and B.
Si: Protons = 14, Neutrons = 14, Electrons = 14
Lewis Structure
Si
14 +
14 n
S2- : 16 protons, 16 neutrons, 18 electrons
-2
S
Be 2+: 4 protons, 5 neutrons, 2 electrons
+2
+2
Be
OR
Be
P: 15 protons, 16 neutrons, 15 electrons
P
B: 5 protons, 6 neutrons, 5 electrons
B