Atomic Theory WS 5
Atomic Structure and Electrons in Atoms Review Sheet
A.
Completion
Use this completion exercise to check your knowledge of the terms and your understanding of the
concepts introduced in this unit. Each blank can be completed with a term, short phrase, or number.
Atoms of each element are different from the atoms of all other elements. Dalton theorized
that atoms are indivisible, but the discovery of subatomic particles changed this theory. We now know
that atoms are made up of electrons, which have a negative charge; protons, which have a positive
charge, and neutrons, which are neutral. The latter two particles are found in the nucleus of the atom.
It was Rutherford who discovered the nucleus of the atom. The nucleus has a positive
charge and it occupies a very small volume of the atom. In contrast, the negatively charged electrons
occupy most of the volume of the atom.
The number of protons in the nucleus of the atom gives the atomic number of that
element. Because atoms are electrically neutral, the number of protons and electrons are equal. The sum of
the protons and neutrons is the mass number. Atoms of the same element are identical in most respects, but
they can differ in the number of neutrons in the nucleus. Atoms that have the same number of protons
but different mass numbers are called isotopes.
The average atomic mass (molar mass) of an element is the weighted average of the masses of the
isotopoes of that element. Two isotopes of sulfur are 3216S and 3416S. are used to make new elements in the lab.
An atom of sulfur-32 isotope contains 16 protons and 16 neutrons.
Each of the three known isotopes of hydrogen has 1 proton(s) in the nucleus. The most common
hydrogen isotope has no neutrons. It has an atomic mass of 1 amu and is called hydrogen-1.
Rutherford pictured the atom as a dense concentration of positive charge (nucleus) surrounded by
orbiting electrons. In the Bohr model, the electrons move in paths of fixed orbits. The quantum mechanical
model is the modern description of the electrons in atoms. This model shows the 90% probability of finding an
electron as a cloud of negative charge. The shape of this cloud is called an orbital.
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Atomic Theory WS 5
The ways in which electrons are arranged around the nuclei of atoms are called electron
configurations. The Aufbau Principle tells us the sequence in which orbitals are filled. The
Pauli Exclusion Principle states that a maximum of only 2 electrons can occupy each orbital, spinning in
opposite directions. Hund’s rule states that the electrons pair up only after each orbital in a sublevel is occupied
by 1 electron.
Every element emits EMR (radiation) if it is heated by passing an electric discharge through its gas or
vapor. Passing this emission through a prism gives unique line spectrum of the element.
B.
True-False
Classify each of these statements as always true (AT); sometimes true (ST); or never true (NT).
__NT___ 1. According to Dalton’s atomic theory, atoms are composed of protons, electrons, and neutrons.
(single particle, like billiard ball)
__AT___ 2. Atoms of elements are electrically neutral.
__NT___ 3. The mass of an electron is equal to the mass of a neutron.
(weighted average – includes protons + neutrons, isotopes)
__AT___ 4. The charge on all protons is the same.
__NT__ 5. The atomic number of an element is the sum of the protons and electrons in the atom.
__NT___ 6. The atomic number of an element is the whole number that decreases as you read across each row
of the periodic table from left to right.
__ST___ 7. An atom of nitrogen has 7 protons and 7 neutrons. (isotopes have different number of neutrons)
__ST___ 8. Relative masses are measured in amus. (or grams, when expressed as molar mass)
__AT___ 9. The number of neutrons in the nucleus can be calculated by subtracting the atomic number from
the mass number.
__AT__ 10. Electrons must have a certain minimum amount of energy, called a quantum of energy, in order
to move from one energy level to a higher energy level.
__ST__ 11. Atomic orbitals are spherical in shape. (s orbitals only)
__NT__ 12. The number of sublevels in an energy level is equal to the square of the principal quantum
number of that energy level.
__S/AT 13. The Aufbau diagram can be used to obtain electron configurations for atoms.
(exceptions are in d and f blocks)
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Atomic Theory WS 5
C.
Problems
Answer the following questions or solve the following problems in the space provided. Show your work.
1. Complete the following table:
Element
Symbol
Atomic #
Mass #
# of protons
# of
electrons
# of neutrons
6C
6
12
6
6
6
19K
19
40
19
19
21
2He
2
4
2
2
2
2+
4
9
4
2
5
37N
7
15
7
10
8
Carbon-12
12
Potassium-40
40
Helium-4
4
Beryllium-9
ion
9
Nitrogen-15
ion
15
4Be
2. Given the relative abundance of the following naturally occurring isotopes of bromine, calculate the average
atomic mass.
Br-79 78.92 amu, 50.69%
Br-81 80.92 amu, 49.31%
78.92 amu x 50.69% = 4000. amu %
80.92 amu, 49.31% = 3990. amu %
7990. amu% 100% = 79.90 amu
3. What is the color and frequency of EMR that has a wavelength of 4.7 x 10-5 cm?
=c

= 3.00 x 108 m = 0.64 x 1015 s-1 = 6.4 x 1014 s-1
4.7 x 10-7 m s
 = 4.7 x 10-5 cm (1 m) (109 nm) = 4.7 x 102 nm = 470 nm BLUE
102 cm
1m
-7
= 4.7 x 10 m
4. Calculate the energy of a quantum of radiant energy whose frequency is 3.82 x 1012 s-1.
(h = 6.626 x 10-34J x s)
E = h
 = 3.82 x 1012 s-1
E = (6.626 x 10-34 J s)( 3.82 x 1012 s-1)
= 25.3 x 10-22 J
= 2.53 x 10-21 J
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Atomic Theory WS 5
5. For each group of sublevels, circle the one that fills last as electrons are added.
a. 3p 2p 1s 2s 3s
b. 4p 3p 2p 4s 4d 5s
c. 3d 4s 3p 3s 2s
6. Write the orbital diagram and complete electron configuration for the potassium atom.
19 e-‘s: 1s22s2sp63s23p64s1

1s

2s




2p

3s

3p


4s
7. What is the element with the electron configuration: 1s22s22p63s23p64s23d7
cobalt
8. Draw electron dot diagrams (Lewis structures) for:
radon
..
: Rn :
..
beryllium
.
Be
.
sulfur
..
.S:
.
nitrogen
.
:N.
.
iodine
..
: I:
.
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