1. Protons, Neutrons, and Electrons
How atoms differ.

2. Bell ringer
How do the masses of neutrons, protons and electrons compare?
A.) neutrons and protons are much larger than electrons
B. ) neutrons and protons are much smaller than electrons
C.) protons and electrons are much larger than neutrons
D.) protons and electrons are much smaller than neutrons
*Hint- Where is most of the mass of an atom?

3. What do we know already? What is an atom?
An atom- is the smallest piece of an element that still represents the element.
Ex) cutting a sheet of aluminum foil into smaller pieces that can no longer be cut further. Is the tiniest piece still aluminum foil?
What are the parts of an atom, Can you tell me?
What are the 3 subatomic particles that make up an atom?
Yes, it still has the same properties and make up as aluminum foil, nothing changes the fact that the piece is still aluminum foil.
The atom is composed of a nucleus and an electron cloud. Within the nucleus there are protons and neutrons; in the electron cloud there are electrons.

4. The parts of an atom Protons and Neutrons have about the same mass
Electrons have much less mass than the other two particles in an atom
Most of the mass of an atom is in the nucleus where the protons and neutrons are

5. This Photo by Unknown Author is licensed under CC BY-SA-NC

6. Different elements- different number of protons
Element- is a substance made from atoms that all have the same number of protons. It is a pure substance of one type of atom.
The number of protons in an atom of an element is the elements Atomic Number
Different elements contain different number of protons, thus they have different atomic numbers.
In a neutral atom, the number of electrons equals the number of protons because the number of negative charges must equal the number of positive charges.
Think back to the aluminum foil example, the smallest piece is still aluminum foil; it doesn’t matter if you have a sheet or a single piece. Therefore, it doesn’t matter if you have one atom of aluminum or a million atoms of aluminum, every atom is representative of the element aluminum.

7. What does the atomic number of the following two elements tell us?
What is the atomic number of Nitrogen?
What is the atomic number of Carbon?
It does not matter if you have one atom that has 7 protons or a million atoms that have 7 protons, it is all representative of nitrogen. Think back to the aluminum foil example, the smallest piece is still aluminum foil; it doesn’t matter if you have a sheet or a single piece.

8. What about neutrons? (Neutrons and isotopes)
The total number of protons and neutrons in an atom is the mass number of an atom.
Isotopes are atoms of the same element that have different numbers of neutrons.
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Do isotopes have the same number of electrons?
Answer: In a neutral isotope, the atom has no charge. Therefore, the number of electrons are still equal to the number of protons.

9. Carbon 12- 6 neutrons, 6 protons
What do we notice is the same? Are all of these isotopes still carbon, why?
Answer: They all have the same number of protons

10. You will always be given the isotope number (it’s the same as the mass number), therefore, you can calculate the number of neutrons.

11. Neutrons and isotopes
The Average Atomic Mass is the average mass of the elements isotopes.
The Avg Atomic Mass is weighted according to the abundance of each isotope.
Abundance simply means: “How much of each isotope”.

12. You should now understand the following learning objectives
What makes an element different?
What are isotopes and how to determine the number of neutrons in each.
How to calculate Average Atomic Mass.