Chapter 3-Revision

The atomic number of an element is

• the mass of the element.

• 1 mol of the element.

• the number of protons in each atom of the element.

• the number of neutrons in each atom of the element.

Hydrogen that is composed of atoms with two neutrons is called

• protium.

• deuterium.

• tritium.

• helium.

Isotopes are atoms of the same element that have different

• masses.

• charges.

• numbers of electrons.

• atomic numbers.

Mass number is

• the average atomic mass of an element.

• the total number of electrons in an atom of an element.

• the total number of protons in an atom of an element.

• the total number of protons and neutrons in an atom of an element.

The isotope uranium-235 has 92 protons and 143 neutrons. Therefore, its mass number is

• 92.

• 235.

• 143.

• impossible to determine.

To take a weighted average of all the naturally occurring isotopes of an element in order to arrive at an average atomic mass, you would

• a. multiply the mass of each isotope by the decimal fraction representing its abundance naturally, then add all these products together.

• b. use the isotope with the largest mass.

• c. use the isotope with the most average mass.

• d. add all the masses of all of the isotopes, then divide by the number of isotopes.

One mole is defined as

• a. the volume of a substance with a mass of 12 g.

• b. the amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12.

• c. the amount of a substance that contains as many particles as there are atoms in exactly 12 g of silver.

• d. an amount of a substance that contains enough atoms to have a mass of 12 g.

The molar mass of an element is numerically equal to the element’s

• a. average number of electrons.

• b. average number of protons.

• c. average atomic mass.

• d. average atomic number.

John Dalton thought that atoms

• a. contain molecules.

• b. cannot be broken down further.

• c. are all composed of carbon.

• d. have no mass.

Using improved chemistry equipment in the late 1700s, chemists observed that mass is neither created nor destroyed in a chemical reaction. This scientific law is called the law of

• a. definite proportions.

• b. gravity.

• c. conservation of mass.

• d. conservation of momentum.