AP Chemistry : Atomic Structure and Properties

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #11 : Mass Spectroscopy Of The Elements

Which of the following isotopes has the greatest number of neutrons?

Possible Answers:

Fluorine-16

Boron-10

Carbon-14

Oxygen-15

Nitrogen-13

Correct answer:

Carbon-14

Explanation:

Carbon-14 has 8 neutrons

Nitrogen-13 has 6 neutrons

Oxygen-15 has 7 neutrons

Fluorine-16 has 7 neutrons

Boron-10 has 5 neutrons

Example Question #21 : Mass Spectroscopy Of The Elements

What is the correct notation of the isotope of nitrogen with 8 neutrons?

Possible Answers:

Nitrogen-15

None of these

Nitrogen-8

Nitrogen-14

Nitrogen-7

Correct answer:

Nitrogen-15

Explanation:

The denotation is element name-proton+neutron. With 7 protons and 8 neutrons, this necomes Nitrogen-15.

Example Question #22 : Mass Spectroscopy Of The Elements

A Carbon-12 atom that has gained a neutron and lost an electron can be described as:

Possible Answers:

an isotope, and a negative ion.

a positive ion only

a negative ion only

an isotope, and a positive ion.

an isotope only

Correct answer:

an isotope, and a positive ion.

Explanation:

Isotopes are examples of the same element existing with different amounts of nuetrons.  When an atom gains a neutron, a different isotope of this atom has been formed.  Ions are atoms that have either completely lost or completely gained an electron when compared to their ground state configuration.  Here the atom has lost an electron and is thus a positive ion. 

Example Question #23 : Mass Spectroscopy Of The Elements

Which of the following is a set of isotopes?

Possible Answers:

 and 

 and 

 and 

 and 

 and 

Correct answer:

 and 

Explanation:

Isotopes are members of the same element that have a different number of neutrons, and therefore a different atomic weight. The number shown in the top left is always the number of protons plus neutrons (atomic weight), so we can show that an element is an isotope by increasing or decreasing that number.

There are three main isotopes of carbon: carbon-12, carbon-13, and carbon-14. The identity of the element must not change, only the atomic weight. The other answer choices are other types of related chemicals; note that ions are not isomers.

Example Question #24 : Mass Spectroscopy Of The Elements

An element has two main isotopes. The first isotope has a molar mass of 125 grams, and the second isotope has a molar mass of 128 grams. A naturally occurring sample of the element has a molar mass of 126.8 grams.

Which of the following statements is true concerning the heavier isotope?

Possible Answers:

It has more protons than the lighter isotope

It has more neutrons than the lighter isotope

It has less neutrons than the lighter isotope

Both isotopes have the same number of nucleons

Correct answer:

It has more neutrons than the lighter isotope

Explanation:

When comparing isotopes to one another, remember that they differ by the number of neutrons in the nucleus. A heavier isotope will have more neutrons when compared to a lighter isotope. The number of protons cannot change, as this would change the elemental identity of the compound. The only way to change the atomic mass of an isotope is to change the number of neutrons.

Example Question #25 : Mass Spectroscopy Of The Elements

The well-known uranium-235 isotope has how many protons, neutrons, and electrons?

Possible Answers:

92 protons, 143 neutrons, and 143 electrons

92 protons, 143 neutrons, and 92 electrons

92 protons, 235 neutrons, and 92 electrons

143 protons, 92 neutrons, and 143 electrons

235 protons, 92 neutrons, and 235 electrons

Correct answer:

92 protons, 143 neutrons, and 92 electrons

Explanation:

We can start by identifying the atomic number of uranium, which will also be equal to the number of protons. For uranium, the atomic number is 92.

The isotope mass is given in the name of the isotope, in this case uranium-235. The total mass (sum of the protons and neutrons) will be equal to 235.

To find the number of neutrons, subtract the number of protons from the total mass: .

Finally, for any neutrally charged molecule, the number of electrons will be equal to the number of protons (92).

Our final answer is 92 protons, 143 neutrons, and 92 electrons.

Example Question #26 : Mass Spectroscopy Of The Elements

Which isotope of nitrogen has the largest atomic radius?

Possible Answers:

The isotopes have the same atomic radius

Correct answer:

The isotopes have the same atomic radius

Explanation:

Atomic radius is generally affected by the interactions of protons and electrons in the atom. Protons attract electrons, condensing the atom, but electrons repel each other, expanding the atom.

Isotopes represent variations in the number of neutrons found in a atom. Neutrons have no charge and neither attract nor repel the electron cloud. As such, increasing the number of neutrons should have no effect on the atomic radius. Each nitrogen isotope has the same atomic radius.

Example Question #27 : Mass Spectroscopy Of The Elements

Which of the following describes an isotope to ?

Possible Answers:

A carbon with 6 protons, 6 neutrons

A carbon with 6 protons, 7 neutrons

A carbon with 8 protons, 5 neutrons

A carbon atom with 7 protons, 6 neutrons

A carbon with 4 protons, 9 neutrons

Correct answer:

A carbon with 6 protons, 6 neutrons

Explanation:

An element is defined by the number of protons it contains. An isotope is the same element with a different number of neutrons; only two choices have six protons, which carbon has. One of them is 13C, which is the same as the question; the other is 12C.

Note that the question asks for an isotope to 13C. By definition, our answer choice cannot be 13C, but must be a variation (an isotope). We are looking for a second answer with 6 protons, in order to maintain the elemental identity of carbon, but a different number of neutrons (not 7). This makes our final answer a carbon atom with 7 protons, 6 neutrons, or 12C, because it is an isotope to 13C.

Example Question #28 : Mass Spectroscopy Of The Elements

How many of each subatomic particle exist in ?

Possible Answers:

130 protons, 52 neutrons, 130 electrons

78 protons, 52 neutrons, 80 electrons

52 protons, 130 neutrons, 54 electrons

130 protons, 130 neutrons, 132 electrons

52 protons, 78 neutrons, 54 electrons

Correct answer:

52 protons, 78 neutrons, 54 electrons

Explanation:

Using the standard isotope notation of , where Z equals the number of protons, and a is the mass number, or the number of protons plus neutrons. Therefore, this isotopic ion has 52 protons and 78 neutrons. Because this anion has a charge of 2-, we know that it contains 54 electrons.

Example Question #29 : Mass Spectroscopy Of The Elements

Which of the following isotopes of carbon is most abundant on Earth?

Possible Answers:

Each isotope is equally abundant

Correct answer:

Explanation:

On the period table, the atomic weight is calculated by averaging the natural abundance of each isotope of the given element. The atomic weight of carbon is 12.011 grams per mole; the abundance of carbon is thus very strongly influenced by the presence of carbon-12.

We can conclude that is the most abundant carbon isotope.

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