Chemistry Reference
In-Depth Information
Answer Key
The actual answers will be shown in brackets, followed by the explana-
tion. If you don't understand an explanation that is given in this section, you
may want to go back and review the lesson that the question came from.
Lesson 3-1 Review
1.
[ion]—Remember: A negative ion has extra electrons, meaning extra
negative charges. A positive ion has lost some of its electrons or negative
charges, leaving it with a net positive charge.
2.
[neutron]—Neutral neutrons are found in the nucleus.
3.
[carbon-12]
4.
[atomic]—The nuclear charge is also equal to the number of protons in the
nucleus of the atom.
5.
[mass]—Because the electrons have so little mass, they are not taken into
consideration when calculating the mass number of an atom.
6.
[isotopes]—Carbon-14 is a radioactive isotope of carbon.
Lesson 3-2 Review
1.
A. [19] B. [26] C. [11] D. [38]
The number of protons is equal to the atomic number, so look in the lower
left-hand corner of the elemental notation.
2.
A. [14]—(27 - 13 = 14) B. [12]—(24 - 12 = 12)
C. [49]—(86 - 37 = 49) D. [15]—(31 - 16 = 15)
The number of neutrons is equal to the mass number—the atomic number.
The mass number is found in the upper left-hand corner of the elemental
notation; the atomic number is found in the lower left-hand corner.
3.
A. [56]—(56 - 0 = 56) B. [25]—(25 - 0 = 25)
C. [10]—(7 - (-3) = 10) D. [2]—(3 - 1 = 2)
The number of electrons can be determined by algebraically subtracting the
charge from the atomic number.
22
11
4.
[D. ]—We must subtract the atomic number from the mass
number to get the number of neutrons. When the atomic number is exactly
half the mass number, then the number of neutrons matches the number of
protons.
Na
12
6
14
6
5.
[D. ]—In order for two elemental notations to represent
different isotopes of the same element, they must have the same atomic
number (number of protons) but a different mass number. Answers A and
B show different elements, because they have different atomic numbers.
X and
X
