Q: A sample contains $$0.50$$ mol of aluminum atoms. How many atoms are present in the sample?

$$3.01 \times 10$$^{23}$$ atoms

Q: Which of the following is the correct formula for calculating the atomic mass of an element with multiple isotopes?

$$\text{Atomic mass} = \sum_n (\text{fraction of isotope } n) \times (\text{mass of isotope } n)$$

Question 1

Which experiment provided the first direct evidence for the existence of the electron as a subatomic particle?

Accepted Answer

J. J. Thomson’s cathode ray tube experiment

Question 2

Which law states that in a chemical reaction, matter is neither created nor destroyed?

Accepted Answer

Law of conservation of mass

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

$$12$$

Question 4

Which of the following statements best explains why the mass of a helium atom is about four times that of a hydrogen atom?

Accepted Answer

Helium has two protons and two neutrons, while hydrogen has one proton and no neutrons.

Question 5

Which of the following is a correct representation of an isotope of carbon with 6 protons and 7 neutrons?

Accepted Answer

$$^{13}_{6}\mathrm{C}$$

Question 6

Which group of elements in the periodic table is characterized by being highly unreactive and having a full valence shell?

Accepted Answer

Noble gases

Question 7

A sample contains $$0.50$$ mol of aluminum atoms. How many atoms are present in the sample?

Accepted Answer

$$3.01 	imes 10$$^{23}$$ atoms

Question 8

Which of the following best describes a cation?

Accepted Answer

An atom that has lost electrons

Question 9

Which of the following elements is a metalloid?

Accepted Answer

Silicon (Si)

Question 10

A naturally occurring sample of chlorine consists of $$75.77\%$$ chlorine-35 (mass $$= 34.97$$ amu) and $$24.23\%$$ chlorine-37 (mass $$= 36.97$$ amu). What is the atomic mass of chlorine?

Accepted Answer

$$35.45$$ amu

Question 11

Which of the following statements is NOT part of Dalton’s atomic theory?

Accepted Answer

Atoms of one element can change into atoms of another element during chemical reactions.

Question 12

Which property is NOT characteristic of metals?

Accepted Answer

Tend to gain electrons in chemical reactions

Question 13

Which of the following best explains the periodic law as observed by Mendeleev?

Accepted Answer

Elements are arranged in order of increasing mass, and certain sets of properties recur periodically.

Question 14

Which of the following ions is most likely formed by a group 2A element?

Accepted Answer

$$\mathrm{M}^{2+}$$

Question 15

How many protons, neutrons, and electrons are in a neutral atom of $$^{23}_{11}\mathrm{Na}$$?

Accepted Answer

11 protons, 12 neutrons, 11 electrons

Question 16

Which of the following best describes the result of Rutherford’s gold foil experiment?

Accepted Answer

Most alpha particles passed through, but some were deflected at large angles, indicating a dense nucleus.

Question 17

Which of the following is the correct formula for calculating the atomic mass of an element with multiple isotopes?

Accepted Answer

$$	ext{Atomic mass} = \sum_n (	ext{fraction of isotope } n) 	imes (	ext{mass of isotope } n)$$

Question 18

A sample contains $$24.0 g of $$carbon. How many moles of carbon are present? (Molar mass of C = $$12.01 g/$$mol)

Accepted Answer

$$2.00$$ mol

Question 19

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 20

Which of the following best describes the charge and mass of a neutron?

Accepted Answer

No charge, mass nearly equal to a proton

Atoms and Elements: Foundations of Matter in Chemistry

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