1. Distinguishing Among Atoms

2. Essential Questions

3. Periodic Table Key

4. Atomic Number
All atoms are made up of protons, neutrons, and electrons
But, every different element has a different number of protons
This # is the atomic number
Example: Oxygen and only Oxygen has 8 protons
Since atoms have a neutral charge, how many electrons must be in each atom?.
So the atomic number is equal to the number of ________ and the number of _______ in each atom..

5. Atomic Mass
Or Mass Number
We know the atomic # tells us the number of H+ (protons) in an atom (and the number of e- (electrons).
Atomic Mass (Mass Number) is more than that. It is how much matter that is in the atom.
Protons, electrons, and Neutrons.
Since Protons and Neutrons are the majority of the mass, the number is close to the number of protons and neutrons added together. (we will talk about the difference later)

6. Atomic Mass How many neutrons in H? In B? In O? In Ne? Or Mass Number
The Atomic number tells us more than just the total mass.
Since we know that atomic mass = all electrons, protons, and neutrons. What would we get if we subtract the atomic number?
Remember, electrons have virtually no mass when compared to protons and neutrons.
How many neutrons in H?
In B?
In O?
In Ne?

7. Atomic Mass
Or Mass Number
If Uranium has an Atomic Mass of 235 and 92 e- , what is the atomic #?
Sometimes chemists write atomic mass, atomic number, and chemical symbol in a shorthand fashion.
For example:
Which is the big #,
Atomic # or Mass#?

8. How many neutrons In each?
Isotopes
Every element has a specific number of protons
If there are a different number of protons, we have a different element.
If we have a different number of neutrons, we do not have a different element. What we have is an isotope.
How many neutrons In each?

9. Atomic Mass What are the atomic #s of each of these isotopes?
What are the Mass #s or each of these isotopes?

10. Atomic Mass

11. Atomic Mass Subatomic particles are extremely small.
The mass of a proton is about 1.67*10-24 g
The mass of a electron is about 9.11*10-28 g
These numbers are really hard to use all the time, so scientists decided to use a standard reference.
Carbon-12 (the most common isotope) has 6 protons and 6 neutrons. These scientists decided to make this element equal 12 atomic mass units (AMU)s
1 AMU = 1/12 of the mass of a Carbon-12 atom

12. Atomic Mass and Relative Abundance
You may have noticed that the atomic masses are not whole numbers.
A little of this difference comes from the electrons, but most of it comes from the isotopes.
*1.0078
*2.0141
Weighted Average

13. Review

14. Essential Questions