Mass, Moles, and Particles

Mass, Moles, and Particles

How to measure quantities of atoms in terms of mass, moles, and particles.

Two Important Numbers for Atoms

• Atomic Number - The number of protons in an atom. This number corresponds to the type of atom it is.

• Mass Number - The sum of the protons and neutrons in an atom. This determines the isotope of the atom.

Isotopes

Isotopes are atoms of the same element which have different mass due to a difference in the number of neutrons in the nucleus. Different elements have varying numbers of isotopes. Tin has 10 stable isotopes (the most of any element).

Naming Isotopes

Important Term!

Nuclide - A general term for a specific isotope of an element.

Important Formulas!

To find the mass number, add the number of protons and number of neutrons

Mass Number = Protons + Neutrons

To find the number of protons, subtract the number of neutrons from the mass number

Number of Protons = Mass Number - Neutrons

To find the number of neutrons, subtract the number of protons from the mass number

Number of Neutrons = Mass Number - Protons

Multiple Choice

What is the mass number of copper-65?

• 65

• 12

• 29

• 63

Fill in the Blanks

Multiple Choice

$$_{28}^{61}Ni$$  

What is the hyphenated notation of the given isotope?

• Nickel-61

• Nickel-28

• Nickel-89

• Nickel-33

​Three Important Numbers

​Molar Mass - The mass of a substance in grams for each mole of that substance.

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​Moles - The amount of the substance present (1 mole is 6.022 x 10²³ particles of the substance).

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​Avogadro's Number - 6.022 x 10²³

​Converting Between Quantities

​There are four basic conversions between moles, mass, and particles:

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​Going from moles to mass, you multiply by the molar mass of the substance.

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​Going from mass to moles, you divide by the molar mass of the substance.

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​Going from moles to particles, you multiply by Avogadro's Number.

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​Going from particles to moles, you divide by Avogadro's Number

​Converting Between Quantities

​Sometimes, you will have to do two conversions to make it to the quantity the problem asks for. For instance, if you are given the number of particles and need to find the mass of the substance, you would have to divide by Avogadro's Number to find the moles of the substance, then multiply by the molar mass to find the total mass of the substance.

Molar Mass

​The molar mass of any element is the same number as the atomic mass on the periodic table.

​The molar mass is how many grams of the substance are in one mole of the substance. Its unit is g/mol.

​Practice!

​You are given 12 moles of Au (gold). How many grams of gold are there?

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​You are handed 4 moles of C (carbon). How many particles of carbon are there in the sample?

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​You are working with 230 grams of Ca (calcium). How many moles of calcium do you have?

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​You are measuring a substance with the atomic number 13. You find you have 91 grams of the substance. How many particles are there of the substance?

Multiple Choice

What is the molar mass of sodium?

• 11

• 22.990

• 45.98

• 3

Multiple Choice

What is the mass of one mole of aluminum?

• 26.982 g

• 13 g

• 53.985 g

• 14 g

Multiple Choice

How many atoms are in 1.50 moles of Hg?

• 9.03x10²³ atoms Hg

• 9.03x10²⁴ atoms Hg

• 903 atoms of Hg

• 9.03 atoms of Hg