Calculate how many neutrons a phosphorus

p. 85, # 1 - 5
p. 85, # 1 - 5
Explain how you can determine the number of neutrons an atom has
from an atom’s mass number and its atomic number.
1. Atomic number is the number of protons only. Mass number is the total
number of protons and neutrons. The number of neutrons is found by
subtracting the atomic number from the mass number.
Calculate how many neutrons a phosphorus-32 atom has.
32 (mass #) – 15 (atomic #) = 17 neutrons in a phosphorus-32 atom.
Name the elements represented by the following symbols.
a. Li Lithium
d. Br Bromine
g. Na Sodium
b. Mg Magnesium e. Hg Mercury
h. Fe Iron
c. Cu Copper
f. S Sulfur
i. K Potassium
p. 85, # 1 - 5
Compare the number of valence electrons an oxygen, O, atom has with
the number of valence electrons a selenium Se, atom has. Are oxygen
and selenium in the same period or group?
4. Both oxygen and selenium have six valence electrons. They are in the
same group.
5. Describe how a sodium ion differs from a sodium atom. Which form of
sodium is more likely to be found in nature? Explain your reasoning.
5. A sodium atom is uncharged and has one valence electron. A sodium ion
is a sodium atom that has lost this valence electron and become Na+. The ion
is more often found in nature because the atom easily loses the valence
electron to achieve a compete outermost energy level.

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