Q: What is the charge of an ion with 17 protons and 18 electrons?

$$\text{Charge} = 17 - 18 = -1$$; the ion has a 1- charge.

Q: A chlorine atom has two naturally occurring isotopes: chlorine-35 (mass 34.97 amu, abundance 75.77%) and chlorine-37 (mass 36.97 amu, abundance 24.23%). What is the atomic mass of chlorine?

$$\text{Atomic mass} = (0.7577 \times 34.97) + (0.2423 \times 36.97) = 35.45\ \text{amu}$$

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

$$\text{Atomic mass} = (0.6011 \times 68.9256) + (0.3989 \times 70.9247) = 69.72\ \text{amu}$$

Question 1

Which statement best describes the difference between an atom and an element?

Accepted Answer

An atom is the smallest identifiable unit of an element, while an element is a substance that cannot be broken down into simpler substances.

Question 2

According to Dalton’s atomic theory, which of the following is NOT true?

Accepted Answer

All atoms of a given element have the same mass and other properties that distinguish them from atoms of other elements.

Question 3

Which experiment led to the discovery that atoms have a dense nucleus?

Accepted Answer

Rutherford’s gold foil experiment

Question 4

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

Accepted Answer

$$	ext{Charge} = 17 - 18 = -1$$; the ion has a 1- charge.

Question 5

Which property is NOT typical of metals?

Accepted Answer

Metals tend to gain electrons during chemical changes.

Question 6

A neutral atom of magnesium has 12 protons. How many electrons does it have?

Accepted Answer

12 electrons

Question 7

Which of the following elements is a metalloid and is widely used in the manufacture of electronic devices?

Accepted Answer

Silicon

Question 8

What is the atomic number ($$Z) of an $$element with 15 protons?

Accepted Answer

$$Z = 15$$

Question 9

A chlorine atom has two naturally occurring isotopes: chlorine-35 (mass 34.97 amu, abundance 75.77%) and chlorine-37 (mass 36.97 amu, abundance 24.23%). What is the atomic mass of chlorine?

Accepted Answer

$$	ext{Atomic mass} = (0.7577 	imes 34.97) + (0.2423 	imes 36.97) = 35.45\ 	ext{amu}$$

Question 10

Which of the following best explains why matter is usually charge-neutral?

Accepted Answer

Matter contains equal numbers of protons and electrons, so their charges cancel.

Question 11

Which group in the periodic table contains the noble gases?

Accepted Answer

Group 8A

Question 12

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

Accepted Answer

$$	ext{Atomic mass} = (0.6011 	imes 68.9256) + (0.3989 	imes 70.9247) = 69.72\ 	ext{amu}$$

Question 13

Which of the following is a correct isotope symbol for an atom with 6 protons and 8 neutrons?

Accepted Answer

$$^{14}_{6}	ext{C}$$

Question 14

Which element has the chemical symbol 'Na' and what is its origin?

Accepted Answer

Sodium; from the Latin 'natrium'

Question 15

Which of the following statements about isotopes is TRUE?

Accepted Answer

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

Question 16

Which element is most likely to form a cation by losing one electron?

Accepted Answer

Sodium (Na)

Question 17

A fluorine atom gains one electron during a chemical reaction. What is the resulting ion and its charge?

Accepted Answer

F$$^-$$; charge = 1-

Question 18

Which of the following is a beneficial use of radioactive isotopes in medicine?

Accepted Answer

Technetium-99 (Tc-99) is used to diagnose disease by imaging internal organs.

Question 19

Which of the following best describes 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.

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

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