Apologia Physical Science Module 13 Study Guide

Define model.

A schematic description of a system that accounts for its known properties

Define nucleus.

The center of an atom, containing the protons and neutrons

Define atomic number.

The number of protons in an atom

Define mass number.

The sum of the numbers of neutrons and protons in the nucleus of an atom

Define isotopes.

Atoms with the same number of protons but different numbers of neutrons

Define element.

A collection of atoms that all have the same number of protons

Define radoiactive isotope.

An atom with a nucleus that is not stable

Define half-life.

The time it takes for half of the original sample of a radioactive isotope to decay

Order the three constituent parts of the atom in terms of their mass, from least massive to most massive.

The three constituents of the atom are the proton, neutron, and electron. The electrons are significantly less massive than the other two, and the neutron is just slightly more massive than the proton. Thus, the order is electron, proton, neutron.

What force keeps the protons and neutrons in the nucleus? What causes this force?

The nuclear force holds the protons and neutrons in the nucleus. This force is caused by the exchange of pions between protons and/or neutrons.

What force keeps the electrons orbiting around the nucleus?

The electromagnetic force (or electroweak force) holds the electrons in orbit. They stay in orbit because they are attracted to the oppositely charged protons.

What is an atom mostly made of?

An atom is mostly empty space.

An atom has an atomic number of 34. How many protons and electrons does it have? What is its atomic symbol?

The atomic number is defined as the number of protons in an atom. Atoms have the same number of electrons as they have protons. Thus, this atom has 34 electrons and 34 protons. The chart tells us that atoms with atomic number of 34 are symbolized by Se.

List the number of protons, electrons, and neutrons for each of the following atoms:

A. Neon-20

B. 56Fe

C. 139La

D. 24Mg

A. Since the chemical symbol is Ne, we can use the chart to learn that the atom has 10 protons. This tells us there are also 10 electrons. The mass number is the sum of protons and neutrons in the nucleus. Thus, there are 10 neutrons.

B. Since the chemical symbol is Fe, we can use the chart to learn that the atom has 26 protons. This tells us there are also 26 electrons. The mass number is the sum of protons and neutrons in the nucleus. Therefore, there are 30 neutrons.

C. Since the chemical symbol is La, we can use the chart to learn that the atom has 57 protons. This tells us there are also 57 electrons. Tha mass number is the sum of the protons and neutrons in the nucleus. Therefore, there are 82 neutrons.

D. Since teh chemical symbol is Mg, we can use the chart to learn that the atom has 12 protons. This tells us there are also 12 electrons. The mass number is the sum of protons and neutrons in the nucleus. Thus, there are 12 neutrons.

Two atoms are isotopes. The first has 18 protons and 20 neutrons. The second has 22 neutrons. How many protons does the second atom have?

In order to be isotopes, the two atoms have the same number of protons. Thus, the second atom also has 18 protons.

Which of the following atoms are isotopes?

112Cd, 112Sn, 120Xe, 124Sn, 40Ar, 120Sn

Isotopes must all have the same number of protons but different numbers of neutrons. Since the chemical symbol tells you how many protons that an atom has, in the end, only atoms with the same chemical symbol can be isotopes. In order to be isotopes, then, the atoms nust have the same chemical symbol but different mass numbers. Thus, 112Sn, 124Sn, and 120Sn are isotopes.

Make sure you can draw a Bohr model of any given atom.

What is the largest Bohr orbit in a Uranium atom (the symbol for uranium is "U"), and how many electrons are in it?

All uranium atoms, regardless of their mass number, have 92 protons and 92 electrons. That's what the chart tells us for any element symbolized with "U." The first two electrons will go in the first Bohr orbit. The next 8 will go in the second Bohr orbit. The next 18 will go in the third Bohr orbit, and the next 32 will go in the fourth Bohr orbit. That makes 60 electrons. The remaining 32 will all fit in the fifth Bohr orbit because it can hold up to 50 electrons. Thus, the largest Bohr orbit is the fifth one, and there are 32 electrons in it.

Why is the strong nuclear force such a short-range force?

The strong nuclear force is governed by the exchange of pions. Some pions have a very short lifetime, so the strong nuclear force can only act over very tiny distances.

Make sure you can determine the daughter products produced by beta decay and alpha decay of radioactive isotopes.

A radioactive isotope goes through radioactive decay, but the isotope's number of protons and neutrons does not change. What kind of radioactive decay occurred?

Only gamma decay does not affect the number of neutrons and protons in a radioactive isotope.

The half-life of the radioactive decay of 226Ra is 1,600 years. If a sample of 226Ra originally had a mass of 10 grams, how mnay grams of 226Ra would be left after 3,200 years?

In 1,600 years, the 10 grams will be cut in half to 5 grams. In the next 1,600 years, those 5 grams will be cut in half to 2.5 grams. That's a total of 3,200 years, so the answer is 2.5 grams.

The half-life of the man-made isotope 11C is 20 minutes. If a scientist makes 1 gram of 11C, how much will be left in one hour?

In one hour, the 11C will have passed through three half-lives. During the first half-life, the 1 gram sample will be rediced to 0.5 grams. During the second half-life, those 0.5 grams will be reduced to 0.25 grams. In the final half-life, those 0.25 grams will be reduced to 0. 125 grams.

Why is radioactive dating unreliable in most situations?

Radioactive dating is usually unreliable because assumptions must be made as to the original condition of the object. These assumptions are usually erroneous.

List the three types of radioactive particles discussed in this module in the order of their ability to travel through matter. Start with the particle that cannot pass through much matter before stopping, and end with the one that can pass through the most matter before stopping.

Aplha particles pass through the least amount of matter before stopping, beta particles are next, and gamma rays pass through the most matter before stopping.