Q: Which of the following is the correct formula for calculating average atomic mass?

$$\text{Average atomic mass} = \sum (\text{isotope mass} \times \text{fractional abundance})$$

Question 1

Which statement best describes the Law of Definite Proportions?

Accepted Answer

A compound always contains two or more elements combined in a definite proportion by mass.

Question 2

Which experiment provided the first measurement of the charge-to-mass ratio of the electron?

Accepted Answer

Thomson's cathode ray tube experiment

Question 3

According to Dalton’s Atomic Theory, which of the following is FALSE?

Accepted Answer

Atoms of a given element can have different masses.

Question 4

A neutral atom of sodium ($$\mathrm{Na}) $$has 11 protons and 11 electrons. What is the electron configuration of a $$\mathrm{Na^+}$$ ion?

Accepted Answer

10 electrons

Question 5

Which of the following best explains why most alpha particles passed through the gold foil in Rutherford’s experiment?

Accepted Answer

Atoms are mostly empty space.

Question 6

Which of the following is a correct statement about isotopes?

Accepted Answer

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

Question 7

Calculate the average atomic mass of lithium if $$^6\mathrm{Li}$$ has a mass of $$6.015\ \mathrm{amu}$$ and an abundance of $$7.42\%$$, and $$^7\mathrm{Li}$$ has a mass of $$7.016\ \mathrm{amu}$$ and an abundance of $$92.58\%.$$

Accepted Answer

$$6.941\ \mathrm{amu}$$

Question 8

Which of the following elements is a metalloid?

Accepted Answer

Silicon ($$\mathrm{Si})$$

Question 9

Which law states that the ratio of the masses of one element that combine with a fixed mass of another element is a simple whole number ratio?

Accepted Answer

Law of Multiple Proportions

Question 10

A sample contains $$^{14}\mathrm{C}$$ atoms. How many protons, neutrons, and electrons are present in a neutral atom of $$^{14}\mathrm{C}$$?

Accepted Answer

6 protons, 8 neutrons, 6 electrons

Question 11

Which of the following ions is a polyatomic ion?

Accepted Answer

$$\mathrm{NO_3$^-}$$

Question 12

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

Accepted Answer

Elements are arranged in order of increasing atomic number.

Question 13

Which of the following elements exists as a diatomic molecule under normal conditions?

Accepted Answer

Nitrogen ($$\mathrm{N_2$})$$

Question 14

A neutral atom of chlorine ($$\mathrm{Cl}) $$has 17 protons and 17 electrons. What is the number of electrons in a $$\mathrm{Cl^-}$$ ion?

Accepted Answer

18 electrons

Question 15

Which of the following best describes a cation?

Accepted Answer

An atom that has lost one or more electrons and has a positive charge.

Question 16

Which of the following is the correct formula for calculating average atomic mass?

Accepted Answer

$$	ext{Average atomic mass} = \sum (	ext{isotope mass} 	imes 	ext{fractional abundance})$$

Question 17

Which subatomic particle was discovered by Chadwick in 1932?

Accepted Answer

Neutron

Question 18

Which of the following ions has the greatest number of electrons?

Accepted Answer

$$\mathrm{S$$^{2-}$$} ($$Sulfur ion)

Question 19

Which property is NOT characteristic of metals?

Accepted Answer

Poor conductor of electricity

Question 20

Which of the following best describes the difference between monatomic and polyatomic ions?

Accepted Answer

Monatomic ions contain only one atom; polyatomic ions contain more than one atom.

Atoms, Molecules, and Ions – Foundations of Atomic Theory

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