The Atom & Nuclear Review Sheet ANSWER KEY

Atomic Structure

1. Complete the following table: subatomic particle location charge
Proton
inside nucleus positive (+)
Electron
outside nucleus negative (-)
Neutron
inside nucleus no charge (neutral)

2. Which subatomic particle has the least mass? electron
3. Why are atoms neutral? the number of positive (+) protons equals the number of negative electrons (-) and the charges cancel each other out (opposite charges attract)

Atoms/Isotopes

4. What unit measures mass of atoms? amu (atomic mass unit)
5. What does the atomic number tell you? the number of protons in the atom/element
6. What does a mass number tell you? the number of protons PLUS the number of neutrons (the sum)
7. What are isotopes? atoms of the same element (same atomic number, same number of protons), but with different numbers of neutrons
8. How does mass number differ from atomic mass? the mass number is simply the number of protons PLUS the number of neutrons while the atomic mass the the weighted average (considering percent abundance) of the masses of all of the isotopes that exist for that element.
9. How are elements arranged on the periodic table? increasing atomic number

10. Use a periodic table to identify the following elements:
a) The element with 47 protons: silver
b) The element with 95 electrons: americium
c) The element with an atomic number of 28: nickel
d) The element with an atomic mass of 35.453 amu: chlorine

12. Complete the following table:
Isotope Name
Mass
Number
Atomic Number
Isotopic
Notation
Number of Protons
Number of Electrons
Number of Neutrons cadmium-112 112
48
Cd
48
48
64
nitrogen – 16
16
7
N
7
7
9 bromine - 80
80
35
Br
35
35
45

13. a) Which isotope of lithium is more abundant: Lithium-5, Lithium-6, Lithium-7? Lithium-7
b) Explain how you know this. the average atomic mass that you see on the periodic table is closest to the lithium-7 mass number indicating that there must be more lithium-7 than the other two
14. a) Three isotopes of Element X occur in nature: X, X, and X. Calculate the average atomic mass of Element X given the following atomic masses and abundances of each of the isotopes: X–36: 35.97 amu and 0.337%
X–38: 37.96 amu and 0.063%
X–40: 39.96 amu and 99.6% remember to put in decimal form!
X–36: 35.97 amu x .00337 = .1212189
X–38: 37.96 amu x .00063 = .0239148
X–40: 39.96 amu x .996 = + .39.80016 39.945292 39.95 amu (need two places past the decimal)

b) What is the identity of the element in the isotopes above? argon *find the element with the atomic mass of 39.95 amu c) Which is the most abundant isotope? argon-40 (it is 99.6% abundant)
Nuclear Chemistry

15. a) What is radiation? tiny waves and particles (capable of traveling at light speed) emitted from a radioisotope
b) What is the name of the instrument used to measure radiation with audible “clicks”? Geiger counter

16. a) Nuclear reactions involve changes in an atom’s nucleus, whereas chemical reactions involve changes in an atom’s electrons.
b) What causes an atom to be unstable? an unstable nucleus/neutron-to-proton ratio
c) If an atom is unstable, it undergoes a process known as radioactice decay to become more stable.
d) The energy and/or particles an atom emits in this process to become more stable are generally known as radiation.
17. Complete the following table:
Type of Radiation
Short-hand Notation
What is it?
Penetration Ability?
Rank 1 as most penetrating and 3 as least penetrating
What can block it? alpha decay, α

slow, heavy helium nucleus (+)
3
paper, skin beta decay, β

fast moving electron (-)
2
thin metals, protective clothing gamma decay, γ

high energy