# Review Worksheet 272 - Unit 3 NAME______KEY__________ 1

```Review Worksheet 272 - Unit 3
1.
Subatomic particle
proton
neutron
electron
NAME______KEY__________
Mass
1 amu
1 amu
0 amu
Charge
positive
neutral
negative
Location
nucleus
nucleus
outside nucleus
2. The number of protons in an atom is the same as its __atomic number___.
3. The sum of the protons and neutrons is its ___mass number___.
4. Atoms that have the same number of protons, but a different number of neutrons are called ____isotopes_____.
5. Calculate the net charge of each:
6.
symbol
1
15
7
N3-
2
23
11
name
Protons
Neutrons
8
10
15
5
11
12
Atomic Mass
number number
Electrons
Charge
10
28
7+
11
0
Protons neutrons electron
s
Charg
e
nitrogen – 15
7
15
7
8
10
3-
Na
sodium – 23
11
23
11
12
11
0
3
18O28
oxygen – 18
8
18
8
10
10
2-
4
24
Mg
12
magnesium - 24
12
24
12
12
12
0
7. Which of these symbols represent isotopes of the same element?
a.
b.
c.
8. The periodic table uses the element _carbon - 12__ for the basis of the atomic masses.
9. The ____average atomic mass__________ of an element is the weighted average of the masses of the
isotopes of the element.
10. Calculate the average atomic mass:
Isotope
magnesium –24
magnesium –25
magnesium –26
mass
relative abundance
23.985
24.986
25.983
78.70% = 18.876
10.13% = 2.531
11.17% = 2.902
24.309 u
11. Neon has two major isotopes, Neon-20 and Neon-22. Out of every 250 neon atoms, 225 will be Neon-20
(19.992 g/mol), and 25 will be Neon-22 (21.991 g/mol). What is the average atomic mass of Neon?
225/250 = 90% and 25/250 = 10%
So… .90(19.992 u) + (.10(21.991 u) = x
17.9928 + 2.1991 = x
20.1919 u = x
12. The atomic mass of lithium is 6.94, the naturally occurring isotopes are 6Li = 6.015121 amu, and
7
Li = 7.016003 amu. Determine the percent abundance of each isotope.
6.015121(X) + 7.016003(1-X) = 6.94
6.015121(X) + 7.016003X - 7.016003) = 6.94
(6.015121x - 7.016003x) = 6.94 -7.016003
-1.000882x = -0.076003
X = 0.075936 = 7.59% so, the other % is 92.41%
13. Write the equation for the decay of polonium-218 by alpha (a) emission.
218
84 Po
14.
4
2
He +
214
82 Pb
Write the equation for the beta (b-) decay of uranium-237
237
92
U
237
93
Np +
0
-1 e
15. Thallium-208 has a half-life of 3.053 min. How long will it take for 120.0g to decay to 7.50 g? 120g/24 =
7.50 g so 4 half life’s – so 12.212 minutes
16. Gold-198 has a half-life of 2.7 days. How much of a 96g sample of gold-198 will be left after 8.1 days?
8.1/2.7 = 3 half lives so 96/23 = 12 grams
17. Which of Dalton’s postulates were not correct? Atoms are indivisible and atoms of the same element are
identical.
18. What did Rutherford conclude from his gold foil experiment? He concluded the there was a positive mass
to the atom called the nucleus.
19. How did the plum pudding model differ from Bohr’s planetary model? Thomson’s plum pudding model
was a positive mass with negative particles and no particular arrangement. Bohr established the idea of
energy levels for the electrons to occupy.
20. What is the difference between an atom’s ground state and its excited state? The ground state is the energy
level an electron normally occupies while the excited state occurs when the atom gains energy and
21. Electrons in the outermost energy level are called ___valence electrons_______.
22. Write the following in orbital box notation:
1s 2s
2p
3s
3p
F
4s
K
Element
F
K
Valence Shell
2
4
Valence electrons
7
1
Kernel electrons
2
18
023. Write the electron configuration for each:
Co
1s22s22p63s23p64s23d7
Ba
1s22s22p63s23p64s23d104p65s24d105p66s2
Element
Co
Ba
Valence Shell
4
6
Valence electrons
2
2
Kernel electrons
25
54
24.
How many p-orbitals would be occupied in an atom of fluorine? 3 p orbitals
25.
What is wrong with the following notation? There is no 2d sublevel and a d-sublevel should have 5
orbitals.
2d
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