Q: A sample of gallium contains 60.11% Ga-69 (mass = 68.9256 amu) and 39.89% Ga-71 (mass = 70.9247 amu). What is the atomic mass of gallium?

$$(0.6011 \times 68.9256) + (0.3989 \times 70.9247) = 69.72$$ amu

Question 1

Which statement best describes the main insight from Rutherford’s gold foil experiment?

Accepted Answer

Atoms are composed of a dense nucleus containing protons and neutrons, with electrons dispersed in mostly empty space.

Question 2

Which of the following is NOT a property of metals?

Accepted Answer

They tend to gain electrons during chemical changes.

Question 3

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

Accepted Answer

$$24 - 12 = 12$$ neutrons

Question 4

Which of the following elements is a halogen?

Accepted Answer

Chlorine

Question 5

What is the charge on an ion with 17 protons and 18 electrons?

Accepted Answer

$$17 - 18 = -1$$; the ion has a $$1-$$ charge

Question 6

Which scientist is credited with the discovery of the electron?

Accepted Answer

J. J. Thomson

Question 7

Which of the following best explains why the atomic mass of chlorine is not a whole number?

Accepted Answer

It is a weighted average of the masses of its naturally occurring isotopes.

Question 8

Which element is defined by having 6 protons in its nucleus?

Accepted Answer

Carbon

Question 9

A sample of gallium contains 60.11% Ga-69 (mass = 68.9256 amu) and 39.89% Ga-71 (mass = 70.9247 amu). What is the atomic mass of gallium?

Accepted Answer

$$(0.6011 	imes 68.9256) + (0.3989 	imes 70.9247) = 69.72$$ 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 group in the periodic table contains elements that are all gases at room temperature and are chemically inert?

Accepted Answer

Noble gases (Group 8A)

Question 12

Which of the following best describes a cation?

Accepted Answer

An ion with more protons than electrons, resulting in a positive charge.

Question 13

Which property is characteristic of metalloids?

Accepted Answer

They have intermediate electrical conductivity that can be controlled.

Question 14

Which of the following is the correct isotope symbol for an atom with 15 protons and 16 neutrons?

Accepted Answer

$$\displaystyle \frac{31}{15}P$$

Question 15

Which of the following best explains why lightning is evidence of electrical charge in matter?

Accepted Answer

Lightning is caused by the rapid rebalancing of positive and negative charges in the atmosphere.

Question 16

Which of the following elements is most likely to form a $$2+$$ ion?

Accepted Answer

Magnesium

Question 17

Which of the following is a correct statement about the periodic law as proposed by Mendeleev?

Accepted Answer

When elements are arranged in order of increasing relative mass, certain sets of properties recur periodically.

Question 18

A technetium-99 ($$^{99}_{43}Tc) $$isotope is used in medical imaging. How many neutrons does it have?

Accepted Answer

$$99 - 43 = 56$$ neutrons

Question 19

Which of the following best describes the difference between a compound and an element?

Accepted Answer

A compound is composed of atoms of different elements combined in simple, whole-number ratios, while an element is a substance that cannot be broken down into simpler substances.

Atoms and Elements: Foundations of Matter (Chapter 4 Study Guide)

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