Understanding Atomic Mass and Mass Number

What is the mass number of an atom?

• The number of protons in an atom

• The sum of protons and neutrons in the nucleus

• The total number of electrons in an atom

• The total mass of an atom in grams

Why is the unified atomic mass unit (U) used instead of grams?

• Because atoms are too large to measure in grams

• Because grams are not a scientific unit

• Because it is easier to calculate with

• Because atomic masses are extremely small

How is the unified atomic mass unit (U) defined?

• As the mass of a single neutron

• As 1/12th the mass of a carbon-12 atom

• As the mass of a single electron

• As the mass of a single proton

What is the atomic mass of carbon-13?

• 13 U

• 14 U

• 12 U

• 15 U

Which of the following has the smallest atomic mass?

• Carbon-12

• Carbon-13

• Hydrogen-3

• Hydrogen-1