Atomic Structure and calculations
Define the nucleus of an atom and name the two types of subatomic particles found there.
The nucleus is the small, dense central region of an atom that contains protons and neutrons
Define "isotope"
Isotopes are atoms of the same element (same number of protons) that have different numbers of neutrons and therefore different mass numbers.
Define "ion" and state what happens to electrons when an atom becomes a positively charged ion.
An ion is an atom or group of atoms with a net electric charge due to loss or gain of electrons. When an atom becomes positively charged (net positive), it has lost one or more electrons.
State one key difference between a chemical reaction and a nuclear reaction.
Chemical reactions involve rearrangement of electrons and form/break chemical bonds without changing nuclei; nuclear reactions change the nucleus (number of protons/neutrons), often changing the element and involving large energy changes.
Define "radioactive decay."
Radioactive decay is the spontaneous transformation of an unstable nucleus into a more stable nucleus by emitting radiation (particles or photons).
Give the atomic number and explain what it represents for an element. (Choose an element)
The atomic number is the number of protons in an atom's nucleus; it uniquely identifies an element and determines its position on the periodic table.
Carbon has isotopes 12 and 14. Give one physical difference and one use of carbon-14.
Physical difference: 14C14C is heavier (has two more neutrons) and is radioactive, while 12C12C is stable. Use of carbon-14: radiocarbon dating of formerly living materials to estimate ages up to ~50,000 years
Give the net charge (with sign) for an atom that loses two electrons from a neutral state.
The net charge is +2+2 (two more protons than electrons).
In which type of reaction (chemical or nuclear) is the identity (element) of an atom changed?
Nuclear reactions change the identity (element) because they change the number of protons in the nucleus.
Name the three of the five most commonly discussed decay types
Alpha (α), beta (β), and gamma (γ) decay.
Neutron and positron also accepted
Which part of the atom contains nearly all of its mass?
The nucleus
An element has two naturally occurring isotopes: 70% with mass 35 u and 30% with mass 37 u. Calculate the average atomic mass (show work).
Average atomic mass = 0.70(35)+0.30(37)=24.5+11.1=35.6
Explain why the number of protons does not change when an atom becomes an ion
Ionization involves gaining or losing electrons (which are external to the nucleus); protons are inside the nucleus and are not changed by ordinary ionization processes.
Describe what an alpha particle is made of
An alpha particle is composed of 2 protons and 2 neutrons (a helium-4 nucleus), symbol 4/2 He
Describe qualitatively how the penetrating power of alpha, beta, and gamma radiation compare (from least to most penetrating).
Least penetrating: alpha < beta < gamma (gamma rays are most penetrating).
Given an atom of fluorine with a mass of 20 and a charge of -1, determine the number of protons, neutrons, and electrons.
9 protons
11 neutrons
10 electrons
Explain why the average atomic mass on the periodic table is not usually a whole number
Because the listed atomic mass is a weighted average of the masses of all naturally occurring isotopes, weighted by their relative abundances, and different isotopes have different mass numbers, producing a non-integer average.
For an atom with atomic number 12 and 12 electrons in neutral form, what is the number of electrons count if it becomes a +2 ion?
10 electrons.
Write the Nuclear equation for the alpha decay of uranium-238.
238U --> 4He + 234Th
Explain what a half-life is
A half-life is the time required for half of a sample of a radioactive isotope to decay.
For chlorine, explain how the isotopes of chlorine's chemical behavior changes and how the value on the periodic table changes.
Chlorine's chemical behavior is governed by its electron configuration (same for isotopes), so isotopes behave chemically the same. The atomic mass on the periodic table (~35.45 u) reflects the weighted average of 35Cl and 37Cl abundances, so it is not a whole number.
If a neutral atom with 17 protons gains two electrons, what is its net charge?
−2
Given the nuclear reaction:
147N + 10n --> ? + 11H
136C
A sample has a half-life of 10 years. If you start with 160 g, how much remains after 30 years...
30 years = 3 half-lives. Remaining mass = 160×(12)3=160×18=20 g160×(21)3=160×81=
20 g.