Q: A sample of gallium contains 60.4% $$^{69}\mathrm{Ga} ($$mass = 68.9257 amu) and 39.6% $$^{71}\mathrm{Ga} ($$mass = 70.9248 amu). What is the atomic weight of gallium?

$$0.604 \times 68.9257 + 0.396 \times 70.9248 = 69.72$$ amu

Question 1

Which of the following statements best describes the difference between isotopes of the same element?

Accepted Answer

They have the same number of protons but different numbers of neutrons.

Question 2

A neutral atom of sulfur has an atomic number of 16 and a mass number of 32. How many neutrons does it contain?

Accepted Answer

$$32 - 16 = 16$$ neutrons

Question 3

Which of the following elements is classified as a metalloid and is commonly used in computer chips due to its semiconducting properties?

Accepted Answer

Silicon (Si)

Question 4

Which group of the periodic table contains elements that are colorless, chemically inert gases at room temperature?

Accepted Answer

Group 8A (Noble gases)

Question 5

A sample of gallium contains 60.4% $$^{69}\mathrm{Ga} ($$mass = 68.9257 amu) and 39.6% $$^{71}\mathrm{Ga} ($$mass = 70.9248 amu). What is the atomic weight of gallium?

Accepted Answer

$$0.604 	imes 68.9257 + 0.396 	imes 70.9248 = 69.72$$ amu

Question 6

Which of the following electron configurations represents a neutral atom of magnesium ($$Z = 12$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$

Question 7

Which of the following best explains why alkali metals (Group 1A) are never found in nature in their pure elemental form?

Accepted Answer

They are highly reactive and readily combine with other elements, especially with water and oxygen.

Question 8

Which of the following statements about the quantum mechanical model of the atom is correct?

Accepted Answer

Electrons are restricted to certain quantized energy levels and are described by wave functions.

Question 9

How many valence electrons does a tin (Sn) atom have, and what is its valence-shell electron configuration?

Accepted Answer

4 valence electrons; $$5s^2$$\ $$5p^2$$

Question 10

Which of the following elements has the electron-dot (Lewis) symbol with five dots around its symbol?

Accepted Answer

Nitrogen (N)

Question 11

A hospital uses a radioactive isotope of iodine, $$^{131}\mathrm{I}$$, for thyroid imaging. Which of the following is true about $$^{131}\mathrm{I}$$ compared to the most common isotope $$^{127}\mathrm{I}$$?

Accepted Answer

$$^{131}\mathrm{I}$$ has the same number of protons but more neutrons than $$^{127}\mathrm{I}.$$

Question 12

Which of the following best describes the trend in atomic radius as you move from left to right across a period in the periodic table?

Accepted Answer

Atomic radius decreases due to increasing nuclear charge pulling electrons closer.

Question 13

Which of the following electron configurations represents a halogen in its ground state?

Accepted Answer

$$[Ne]\ 3s^2$\ 3p^5$

Question 14

A certain atom has 2 electrons in the first shell, 8 in the second shell, and 4 in the third shell. What is the identity of this element?

Accepted Answer

Silicon (Si)

Question 15

Which of the following is the correct shorthand electron configuration for zirconium (Zr, $$Z = 40$$)?

Accepted Answer

$$[Kr]\ 5s^2$\ 4d^2$

Question 16

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group have similar chemical properties due to similar valence electron configurations.

Question 17

Which of the following is the general valence-shell electron configuration for group 6A elements?

Accepted Answer

$$ns^2$$\ $$np^4$$

Question 18

A patient is exposed to a small amount of $$^{60}\mathrm{Co} ($$cobalt-60) during cancer treatment. How many neutrons are present in a $$^{60}\mathrm{Co}$$ atom?

Accepted Answer

$$60 - 27 = 33$$ neutrons

Question 19

Which of the following best describes the electron arrangement in the 2p subshell of a nitrogen atom ($$Z = 7$$)?

Accepted Answer

Each of the three 2p orbitals contains one electron, all unpaired.

Atoms and the Periodic Table: Structure, Properties, and Electron Configurations

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