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Isotopes - P. 496 - P. 494
Physical Science Classwork 02/17/17
PS.05, 06
1) How are the number of neutrons in the nucleus of an atom calculated?
A) add the number of electrons and protons together
B) subtract the number of protons from the mass number
C) add the mass number to the number of electrons
D) subtract the number of electrons from the number of protons
1)
2) How do the isotopes hydrogen-1 and hydrogen-2 differ?
A) Hydrogen-2 has one neutron; hydrogen-1 has none.
B) Hydrogen-2 has two protons; hydrogen-1 has one.
C) Hydrogen-1 has no protons; hydrogen-2 has one.
D) Hydrogen-2 has one more electron than hydrogen-1.
2)
3) How do the isotopes helium-3 and helium-4 differ?
A) Helium-4 has one more electron than helium-3.
B) Helium-3 has no protons; helium-4 has one.
C) Helium-4 has four protons; helium-3 has three.
D) Helium-4 has two neutrons; helium-3 has one.
3)
AVERAGE ATOMIC MASS - P. 497
4) Why do chemists use relative comparisons of masses of atoms?
A) The actual masses of protons and neutrons are very small.
B) The number of subatomic particles in atoms of different elements varies.
C) The actual mass of an electron is very large compared to the actual mass of a proton.
D) The actual masses of protons, electrons, and neutrons are not known.
5) What unit is used to measure average relative atomic mass?
4)
5)
6) Which of the following equals one atomic mass unit?
A) the mass of one carbon atom
B) one-twelfth the mass of a carbon-12 atom
C) the mass of one helium atom
D) the mass of one electron
6)
7) Why is carbon-12 used as the basis for the atomic mass unit?
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8) The atomic mass of an element as shown on the periodic table is equal to _____.
A) the weighted average of the masses of the isotopes of the element
B) the average of the number of protons, neutrons and electrons in its nucleus
C) the average of the mass number and the atomic number for the element
D) the total number of subatomic particles in its nucleus
E) the total mass of the isotopes of the element
8)
9) In order to calculate the weighted average of all the isotopes of an element, you need to know the
___________________ of isotopes, the ____________ of each, and the relative _______________________
(percentage) of each isotope.
10) The atomic mass of an element _____.
A) depends upon the relative abundance of each isotope of the element
B) depends upon the number of isotopes of that element
C) depends upon the mass of each isotope of that element
D) all of the above
10)
TO CALCULATE AVERAGE ATOMIC MASS:
1. Write the mass of the first isotope (as many digits as the problem gives), times its percentage
(converted to a decimal), an equal sign, and the product.
2. Repeat for each isotope.
3. Add up all the products. The answer is the weighted average.
Mass-1
x percent-1 as decimal =
product1
Mass-2
x percent-2 as decimal =
product2
Weighted Average
11) Naturally occurring silver consists of two isotopes: 51.82% Ag-107, and 48.18% Ag-109.
Calculate the atomic mass of silver.
11)
12) Consider an element X that has two naturally occurring isotopes with the following
percent abundances: the isotope with a mass number of 40 is 25% abundant; the isotope
with a mass number of 42 is 75% abundant. What is the atomic mass for element X?
12)
13) What is the atomic mass of hafnium if 5.00% of its atoms have mass 176, 19.0% have mass
177, 27.0% have mass 178, 14.0% have mass 179, and 35.0% have mass 180.0?
13)
14) There are four naturally occurring isotopes of the element chromium. The relative
50Cr = 4.31%, 52Cr = 83.76%, 53Cr = 9.55%, 54Cr = 2.38%.
abundance of each is:
Calculate the average atomic mass of chromium.
14)
15) What is the difference between mass number and atomic mass?
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16) Explain why atomic masses are not whole numbers.
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