Atomic Number and Mass Number

Atomic Number and Mass Number

physical science

Multiple Choice

What makes up most of the mass of an atom?

• electron cloud

• empty space

• nucleus

Atomic Number

• each element has its own atomic number that never changes

• each element has a specific number of protons

• Thorium's atomic number is 90, so ALL Thorium atoms will have 90 protons

Multiple Choice

What does atomic number tell us?

• number of protons

• number of neutrons

• number of protons + neutrons

• number of protons + electrons

Multiple Choice

You find out that an atom has 5 protons, 6 neutrons, and 5 electrons. What is this atom's atomic number?

• 5

• 6

• 11

• 1

Mass Number

• the mass number of the previous example is 12

• mass number is calculated by ADDING the number of protons and neutrons

Multiple Choice

You find out that an atom has 5 protons, 6 neutrons, and 5 electrons. What is this atom's mass number?

• 5

• 6

• 11

• 1

Calculating the number of neutrons

• find the MASS number of the atom; mass number includes the number of protons and neutrons

• find the ATOMIC number of the atom; atomic number is only the number of protons

• MASS number - ATOMIC number = number of neutrons

• (protons and neutrons) - protons = neutrons

Multiple Choice

An atom with 18 protons has a mass number of 40. How many neutrons are in the nucleus?

• 18

• 40

• 58

• 22

8 protons means atomic number = 8

16 - 8 = 8 neutrons

Finding the number of electrons

• REMEMBER: the overall charge of the atom is NEUTRAL

• for this to be true, protons (+) and electrons (-) have to cancel each other out

• therefore, 8 protons = 8 electrons

Multiple Choice

You know that an atom has 13 protons and 14 neutrons. How many electrons does this atom have?

• 13

• 14

• 1

• 27

Multiple Choice

What is the atomic number of this element?

• 10

• 20.1797

Multiple Choice

How many protons will an atom of Silicon have?

• 28.086

• 14

• 42

• 15

Multiple Choice

How many neutrons will an atom of Lithium have?

• 3

• 7

• 4

• 10

Multiple Choice

How many electrons will there be in an atom of Manganese?

• 25

• 55

• 40

• 80

Multiple Choice

Calculate the number of neutrons in an atom of Krypton.

• 36

• 84

• 120

• 48

Multiple Choice

Isotopes have a different number of:

• protons

• neutrons

• electrons

• quarks