Q: A sample of gallium contains two isotopes: $$^{69}\mathrm{Ga} ($$atomic mass 68.926 amu, 60.10%) and $$^{71}\mathrm{Ga} ($$atomic mass 70.925 amu, 39.90%). What is the atomic mass of gallium?

$$68.926 \times 0.6010 + 70.925 \times 0.3990 = 69.72\ \mathrm{amu}$$

Question 1

Which of the following statements best describes an element?

Accepted Answer

An element is a pure substance that cannot be broken down into simpler substances.

Question 2

Which of the following elements is a metalloid?

Accepted Answer

Silicon

Question 3

What is the correct chemical symbol for the element potassium?

Accepted Answer

K

Question 4

Which group on the periodic table contains the alkali metals?

Accepted Answer

Group 1A (1)

Question 5

A neutral atom of magnesium has an atomic number of 12 and a mass number of 24. How many neutrons does it have?

Accepted Answer

$$24 - 12 = 12$$

Question 6

Which of the following best explains why atomic size increases as you move down a group in the periodic table?

Accepted Answer

The number of energy levels increases, placing valence electrons farther from the nucleus.

Question 7

Which element is most likely to have the highest ionization energy?

Accepted Answer

Fluorine (F)

Question 8

Which of the following is the correct electron configuration for oxygen (atomic number 8)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^4$$

Question 9

A sample of gallium contains two isotopes: $$^{69}\mathrm{Ga} ($$atomic mass 68.926 amu, 60.10%) and $$^{71}\mathrm{Ga} ($$atomic mass 70.925 amu, 39.90%). What is the atomic mass of gallium?

Accepted Answer

$$68.926 	imes 0.6010 + 70.925 	imes 0.3990 = 69.72\ \mathrm{amu}$$

Question 10

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 11

Which of the following elements is a nonmetal found in Group 5A (15)?

Accepted Answer

Nitrogen

Question 12

Which of the following best describes the Pauli exclusion principle?

Accepted Answer

Each orbital can hold a maximum of two electrons with opposite spins.

Question 13

Which of the following elements is most likely to be used as a semiconductor in electronic devices?

Accepted Answer

Silicon

Question 14

Which of the following is the correct Lewis symbol for carbon?

Accepted Answer

The symbol C with four single dots, one on each side.

Question 15

Which of the following trends is correct for the representative elements in the periodic table?

Accepted Answer

Ionization energy decreases from top to bottom within a group.

Question 16

Which of the following best explains why metals are good conductors of electricity?

Accepted Answer

Metals have loosely held valence electrons that can move freely.

Question 17

Which of the following is the correct order of filling for electron sublevels as atomic number increases?

Accepted Answer

$$1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d$$

Question 18

Which of the following elements has the electron configuration $$[\mathrm{Ar}]\ 4s^2$\ 3d^7$?

Accepted Answer

Cobalt (Co)

Question 19

Which of the following statements about the nucleus of an atom is correct?

Accepted Answer

The nucleus contains protons and neutrons and accounts for most of the atom's mass.

Question 20

Which of the following best describes the trend in metallic character across a period from left to right?

Accepted Answer

Metallic character decreases.

Atoms and Elements – Study Notes for GOB Chemistry

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