Chemistry
Name_________________________
Atomic Structure
Period______Date_______________
I. OBJECTIVES:
A. The three atomic particles: the proton, the neutron and the electron. You should be aware of their mass
and charge relationships.
B. The reason for the neutrality of atoms: since it is the protons and electrons which contain the positive and
negative charges, you can say that in order to be electrically neutral, atoms have equal numbers of
protons and electrons.
C. Atomic number is the number of protons in an atom. Mass number is the sum of the protons and
neutrons in an atom. Isotopes are atoms of the same element that differ only in the number of neutrons
(and therefore, their mass numbers and masses.)
D. Write an isotopic symbol.
E. Atomic mass of an element is the weighted average of the mass numbers of all the isotopes of that
element. This average takes into account the proportion in which the isotopes occur in nature.
F. An ion is a charged atom that has lost or gained electrons. If an atom loses electrons, it is positively
charged and is called a cation. If an atom gains electrons, it is negatively changed and is called an anion.
G. Work with various concepts and definitions related to atomic number, mass number, charge, isotopic
symbols and ions.
H. Determine the atomic number, mass number, how many protons, neutrons and electrons are present in an
atom, charge of an ion, write correct symbols for isotopes.
II. PROBLEMS:
1. Summarize the information you have gained about subatomic particles in the table below:
Relative Mass
Location in the
Particle
Symbol
Electrical Charge
(AMU)
Atom
electron
neutron
proton
2. Why are atoms electrically neutral?______________________________________________________
1 - Atomic Structure Packet
3. Define the following terms:
A. atomic number
B. mass number
C. isotope
D. isotopic symbol
E. average atomic mass
F. ion
G. charge
4. A. A nitrogen atom has 7 protons and 7 neutrons. Calculate:
1. the atomic number ______
2. the mass number ______
B. A phosphorus atom has 15 protons, 18 electrons, and 16 neutrons. Calculate:
1. the atomic number ______
5.
2. the mass number ______
3. the charge
If a sulfur atom is neutral in charge and contains 16 protons in the nucleus, how many electrons are
present outside the nucleus? ______
6. Write the isotopic symbol for a lithium atom with 3 protons and 4 neutrons: _________
7. Which of the following are isotopes of each other? Why?______________________________________
A)
32
16
S
B)
36
16
S -2
C)
36
18
Ar
8. An isotope of silver has 47 protons, 46 electrons and 60 neutrons.
A) What is the atomic number? ______
D) Write the complete isotopic symbol for the element:
B) What is the mass number? ______
C) How many electrons are present? ______
9. Circle the one in each of the pairs of elements has the most neutrons.
A)
29
9
F
or
21
10
2 - Atomic Structure Packet
Ne
B)
42
20
Ca
or
46
22
Ti
10. In a nuclear reactor, an isotope of uranium, called U-235, is used. It has 92 protons and a mass number
of 235.
A) What is the atomic number? ______
D) Write the complete isotopic symbol
for the element:
B) How many electrons are present? ______
C) How many neutrons are present? ______
11. Complete the following table for each of the isotopes listed:
18
8
O -2
45
21
Sc
84
36
3
1
Kr
H +1
What is the atomic number?
What is the mass number?
How many protons?
How many neutrons?
How many electrons?
11. For each of the following pairs of elements, decide whether or not the pairs of elements are isotopes or
completely different elements.
A) Element A has 22 protons and 24 neutrons. Element B has 22 protons and 25 neutrons. __________
B) Element C has 29 protons and 34 neutrons.
Element D has 30 protons and 34 neutrons. __________
C) Element E has 24 protons and a mass of 50. Element F has the isotopic symbol
52
24
X . _____________
D) Element G has an atomic number of 28 and a mass of 64. __________________________________
Element H has 30 protons and the symbol 64
30 X .
E) Element I is neutral and has 78 electrons and 117 neutrons. _________________________________
Element J has the isotopic symbol 196
78 X .
12. A. An atom contains 15 protons, 16 neutrons and 15 electrons. Write the isotopic symbol: ___________
B. Write the isotopic symbol for a possible isotope of this atom: ___________
C. If the atom gains three electrons, write the isotopic symbol for the ion: ___________
3 - Atomic Structure Packet
13. Complete the following table:
Isotope
Atomic
Symbol
Name
Number
Mass
Number
Protons
Neutrons
Electrons
Sodium-23
Charge
0
57
26
Fe +2
27
32
15
32
7
+2
10
72
0
19
13
10
20
18
51
23
+3
0
14. With the help of the periodic table, tell the number of protons, neutrons and electrons in each of the
following isotopes:
A. carbon-14
p: _______ n:_______ e: _______
B. cobalt-60
p: _______ n:_______ e: _______
C. bromine-81
p: _______ n:_______ e: _______
D. strontium-90 p: _______ n:_______ e: _______
E.
27
13
Al +3
p: _______ n:_______ e: _______
F.
84
36
Kr
p: _______ n:_______ e: _______
G.
40
20
Ca +2
p: _______ n:_______ e: _______
H.
4
2
He
p: _______ n:_______ e: _______
15. Write isotopic symbols for neutral atoms with:
A. 9 p+ and 10 no __________
C. 31 p+ and 39 no
B. 25 p+ and 30 no ___________
D. 1 p+ and 0 no __________
4 - Atomic Structure Packet
__________
16. Which of the following atoms are isotopes?
A.
24
12
X
B.
12
6
X
C.
52
24
D. 63 X
X
E.
24
11
F.
X
23
11
X
17. Consult the periodic table and identify each of the elements listed in #16 above.
A. ________________
B. __________________
C. ___________________
D. ________________
E. __________________
F. ___________________
18. A certain isotope of cobalt is five times as heavy as
12
6
C . What is the mass number of this isotope? _____
19. Choose the best answer from the choices given and circle its number.
A. Neutral atoms have…
1) more negative charge than positive charge.
2) more positive charge than negative charge.
3) equal amounts of positive and negative charge.
4) variable charge.
B. The particle having the greatest actual mass is the…
1) electron
2) neutron
3) neutrino
4) proton
C. A particle that is present in every atom is the…
1) positron
2) proton
3) neutron
4) neutrino
D. The charge on the nucleus of an atom is due to…
1) neutrons
2) positrons
3) protons
4) electrons
E. All atoms of a given element have the same…
1) number of nucleons
3) number of neutrons
2) number of protons
4) mass number
F. Which atomic particle would NOT be deflected by an electrical field?
1) neutron
2) alpha particle
3) beta particle
4) proton
G. The neutrons of an atom…
1) revolve around the nucleus
2) contribute to atomic mass
3) are positively charged
4) determine atomic number
H. The subatomic particles which have equal but opposite charges are…
1) proton and electron
3) nucleus and neutron
2) proton and neutron
4) electron and neutron
I. Which particle has the least mass?
1) proton
2) neutron
3) alpha particle
4) electron
J. A pure substance whose atoms all have the same atomic number is a(n)…
1) compound
2) element
3) radical
4) mixture
5 - Atomic Structure Packet
K. Isotopes of an element have the same…
1) make-up of the nucleus
3) number of protons
2) number of atoms
4) number of neutrons
L. An atom containing 9 protons, 10 neutrons and 9 electrons has a mass number of…
1) 9
2) 18
3) 19
4) 28
M. As the number of neutrons in the nucleus of an atom increases, the atomic number of the element…
1) decreases
2) increases
3) remains the same
N. As the atomic numbers of the elements increases, the number of protons in the nucleus
1) decreases
2) increases
3) remains the same
O. The symbols 11 H , 21 H , and 31 H show that the three kinds of hydrogen atoms have…
1) the same atomic mass
3) the same number of protons
2) different atomic numbers
4) the same number of neutrons
P. The number of neutrons in the nucleus of a 31 H atom is…
1) 1
2) 2
3) 3
4) 4
Q. As the atomic mass of chlorine isotopes increases, the number of protons…
1) decreases
2) increases
3) remains the same
R. The number of protons in the nucleus of an oxygen atom is…
1) 8
2) 9
3) 20
4) 17
S. The number of neutrons in the nucleus of 37
17 Cl is…
1) 17
2) 18
3) 20
4) 37
T. The atom whose nucleus contains the largest number of neutrons is…
1) 245
2) 237
3) 239
4) 239
95 Am
93 Np
93 Np
92 U
U. The symbol which shows phosphorus with a mass number of 31 is…
31
P
1) 15
2) 30
3) 16
4) 15
31 P
15 P
15 P
V. What is the correct symbol for an element containing 6 protons and 8 neutrons…
1) 126 C
2) 146 C
3) 168 O
4) 148 O
W. If an atom gains an electron, it becomes…
1) a cation
2) an anion
3) neutral
X. A negative two (-2) charge indicates that the atom…
1) gained two electrons
3) gained two protons
2) lost two electrons
4) lost two protons
6 - Atomic Structure Packet
20. Average Atomic Mass: Use the concept of isotopes to explain why the atomic masses of elements
are not whole numbers. ___________________________________________________________________
Example: Use the following information to determine the atomic mass of chlorine. Two isotopes are
known: chlorine-35 (mass = 35.0 amu) and chlorine-37 (mass = 37.0 amu). The relative abundances are
75.4% and 24.6%, respectively.
Solution: Recall that the text defines atomic mass as the weighted average of the masses of the isotopes of
that element. To solve the problem:
Contribution of masses by each isotope = mass of isotope x relative abundance =
=
35.0 amu x 0.754
= 26.4 amu
=
37.0 amu x 0.246
= 9.10 amu
The sum of the individual isotope mass contributions will equal the atomic mass.
26.4 amu
+
9.10 amu
= 35.5 amu
Problems:
A. Two isotopes are known: carbon-12 (mass = 12.00 amu) and carbon-13 (mass = 13.00 amu). Their
relative abundances are 98.9% and 1.10% respectively. Determine the atomic mass of carbon.
B. Given the relative abundance of the following naturally occurring isotopes of oxygen, calculate the
average atomic mass of oxygen:
99.76% oxygen-16
0.037% oxygen-17
0.204% oxygen-18
C. Determine the atomic mass of an element which has 2 isotopes with numbers of 6 (mass = 6.02) and 7
(mass = 7.02). The relative abundances are 7.42% and 92.6%, respectively.
D. Calculate the average atomic mass of an element from isotope data. Element Y has 2 isotopes.
One has a mass number of 10, and a relative abundance of 20.%. The other isotope has a mass number of
11 and a relative abundance of 80.%.
7 - Atomic Structure Packet
Atomic Structure Review Sheet
Atoms of each element are ______________________ from the atoms of all other elements. Dalton
theorized that atoms are indivisible, but the discovery of _________________ particles changed his theory.
We now know that atoms are made up of electrons, which have a _______________________ charge;
__________________, which have a positive charge; and ___________________, which are neutral. The
latter two particles are found in the _____________________ of the atom.
It was ______________________ who discovered the nucleus of the atom. The nucleus has a
____________________ charge and it occupies a very small volume of the atom. In contrast, the negatively
charged __________________ occupy most of the volume of the atom.
The number of _________________________ in the nucleus of the atom is the atomic
____________________ of that element. Because atoms are electrically neutral, the number of protons and
_____________________ in an atom are equal. The sum of the __________________ and neutrons is the
mass number. Atoms of the same element are identical in some respects, but they can differ in the number of
________________ in the nucleus. Atoms that have the same number of protons but have different mass
numbers are called _______________________.
The ______________________ of an element is the weighted average of the masses of the isotopes of
that element. Two isotopes of sulfur are 32
16 S and
34
16
S . An atom of the sulfur-32 isotope contains
_______________ protons and ______________ neutrons. The sulfur-34 isotope has _______________
protons and ______________ neutrons.
Each of the three known isotopes of hydrogen has ________________ proton(s) in the nucleus. The
most common hydrogen isotope has ________________ neutrons. It has a mass number of
________________ amu and is called hydrogen-1.
8 - Atomic Structure Packet