Atomic Mass Units

Atomic Number, Mass, and Isotopes Lab Synthesis Project

by Sofia Ziran 8-1

​Intro

​In this lesson, we will be expanding on atoms and elements.

​Just as a review, an element refers to the same type of atom with the same number of protons.

​What is Atomic Number?

​​Atomic Number is the number of protons found in an elemts. Atoms of the same elements have the same number of protons which means that they have the same atomic number.

​What is Atomic Mass? 

​Atomic Mass is the mass of an atom. It is measured in atomic mass unit (amu). The sum of protons and neutrons in an atom make up the atomic mass. Electrons are not part of the atomic mass because they have no significant mass, while protons and neutrons are both about 1 amu.

​How are Atomic Mass and Number Related?

​​Atomic Number + Neutrons= Atomic Mass

​

​This equation can help you find the number of protons and neutrons in an atom. If you know the atom's atomic number and the number of neutrons, you can add them together to find the atom's atomic mass. If you know that atom's atomic mass and atomic number, you can calculate the number of neutrons in the atom. If you assume that the atom is neutral, you can determine the number of electrons using the atomic number (which is the same as the number of protons). This is because the number of electrons and protons in a neutral atom must balance out. 

Multiple Choice

If an atom has 6 protons, 7 neutrons

and 6 electrons. What is the atom’s

atomic number and atomic mass?

Multiple Choice

A neutral atom has an atomic mass

of 16 and an atomic number of 8.

Use the atom’s atomic number and

atomic mass to find the number of

protons, neutrons and electrons in

the atom.

Multiple Select

If you assume an atom is neutral, an you know the atom's mass and the number of electrons it possesses, can you determine its atomic number? the number of neutrons in the atom?

• yes; (atomic #) the number of protons and electrons in a neutral atom are the same

• yes (# of neutrons): since you have # of protons/atomic #, you can subtract it from the atomic mass to find it 

• No (both) the atom is an isotope so you have no way of knowing

Multiple Choice

What is the difference between

atomic mass and atomic number?

• the atomic mass is measured in amu while the atomic number is measured in mph 

• the atomic mass is the number of protons in an atom, whereas atomic number is the sum of protons and neutrons in an atom

• the atomic number is the number of protons in an atom, whereas atomic mass is the sum of protons and neutrons in an atom

Multiple Choice

Why aren't electrons considered when determining an atom's atomic mass?

• b/c they are not part of the nucleus

• b/c they have no significant mass , compared to protons & neutrons

• b/c they have no weight

​What are Isotopes?

​Isotopes are a different form of an element. They are made when there is a change in the number of neutrons of an atom. They're still the same element as before the neutron change, because the number protons hasn't changed. Unstable isotopes are called radioactive isotopes. In order to become stable, radioactive isotopes emit radiation, which can cause cancer in humans. Although naturally occuring radioactive isotopes are dangerous, they have many beneficial applications. For example Uranium-235 can be used as fuel for nuclear power plants.

​common isotopes:

​

​- iodine-131, iodine-129

​- fluorine-17, fluorine-18, fluorine-20

​

​-

​

​

​-

​What is Average Atomic Mass?

​Average Atomic Mass is the average abundance of all the naturally occurring isotopes of an element. It is important because it can help you determine the most common form of an element, and we can use it to compare and categorize elements.

Multiple Select

What is an isotope?

• different form of an element

• occurs when the number of neutrons in an atom changes 

• occurs when the number of electrons in an atom changes

• different element completely

Multiple Choice

Many large atoms, which naturally

have many protons, neutrons and

electrons, only have radioactive

isotopes. Why does this make

sense?

• the number of nuclei in the nucleus may vary which causes the atom to be unstable

• the number of neutrons in the nucleus may vary which causes the atom to be unstable

• the number of electrons in the nucleus may vary which causes the atom to be unstable

• the number of protons in the nucleus may vary which causes the atom to be unstable

Multiple Select

Why are radioactive isotopes dangerous?

• they can cause cancer, which we don't have a cure for yet

• they emit radiation to become stable. This radiation can destroy/harm the cells of living things

• they explode when exposed to high temperatures

Multiple Select

Why is it important to consider average atomic mass?

• it can help you determine the most common form of an element

• because it tells you how much an atom weighs

• we can use it to compare and categorize element