Path to Mastering LT 2.3 - Atomic Number vs mass number

What is the atomic number of an element?

• The number of protons in the nucleus of an atom

• The total number of protons and neutrons in an atom

• The average mass of all isotopes of an element

• The number of electrons in a neutral atom

Answer explanation

Atomic number = the number of protons

Which of the following best describes the mass number of an element?

• The number of protons in the nucleus

• The number of neutrons in the nucleus

• The total number of protons and neutrons in an atom

• The average mass of all isotopes of an element

Answer explanation

Mass number = protons + neutrons

Which of the following statements is true about atomic number?

• It is always greater than the mass number.

• It is equal to the number of neutrons in an atom.

• It determines the identity of an element.

• It is the average mass of all isotopes of an element.

Answer explanation

Atomic number = the number of protons in an atom. The number of protons identify the element.

If an atom has 6 protons and 8 neutrons, what is its mass number?

• 6

• 8

• 14

• 12

Answer explanation

Mass number = protons + neutrons

Explain why the atomic mass of an element is not a whole number.

• Because it is the sum of protons and neutrons.

• Because it is the average of the masses of all isotopes of that element.

• Because it is the number of protons in the nucleus.

• Because it is the number of neutrons in the nucleus.

Answer explanation

The atomic mass printed on the periodic table is a weighted average of all the naturally occurring isotopes of that element.

Identify the parts of the periodic table element shown.

a

b

c

d

Atomic mass

Element Name

Element Symbol

Atomic Number

Answer explanation

Tags

NGSS.MS-PS1-1

The mass number of this atom is ​ (a)   and the atomic number of this atom is ​ (b)   ?

• 4
• 6
• none of the above
• 2
• 1

Answer explanation

Mass number = protons + neutrons and atomic number = protons

Tags

NGSS.MS-PS1-1