1. Atoms, Isotopes, and Bohr!

2. What makes up an atom?
An atom is made up of subatomic particles (protons, neutrons, and electrons.) Protons and neutrons are made up of Quarks.
An element is made up the same type of atom.

3. Parts of the Atom Neutron Proton Electron
What do you notice about the size of each type of particle?
Proton
Electron

4. What does an atom really look like?
An atom has a very dense center called a nucleus where the protons and neutrons are located. The electron cloud is the space around the nucleus. The dots show where an electron is likely to be.

5. Parts of the Atom Charge Mass (amu) Location Proton + 1
1 (very large!)
nucleus
Neutron
Electron
- 1
.0005 (very very small!)
outside nucleus
Parts of the Atom

6. What holds an atom together?
Because protons have a positive charge and electrons have a negative charge, they are attracted to each other because of the electromagnetic force (opposite charges attract, like charges repel.)

8. Atom Diagrams
We diagram an atom with electrons moving in electron shells around the nucleus.
The farther away the electron is from the nucleus, the more energy the electron has.
Electrons in energy levels are grouped in pairs.

9. Let’s Review What does the atomic number tell you?
How do you find the number of neutrons?

10. Bohr Model Electron Shells

11. Bohr Model Practice

12. So let’s try it…. Li Lithium How to draw a Lithium atom
First, look at the Periodic Table
Second, determine the number of protons the atomic number)
Then determine the number of neutrons (Atomic mass – atomic number)
Then determine the number of electrons the atomic number) 3 Li
Lithium 7

13. So let’s try it…. Li Lithium Protons = 3 3 7 Neutrons = 4 (7-3=4) - +
Electrons = 3
2 in the 1st shell, 1 in the 2nd shell
Neutrons = 4
(7-3=4)

14. Isotopes
An isotope is an atom that has the same number of protons, but a different number of neutrons.

15. Isotopes (continued)
You can think of isotopes like atoms having a twin or triplet. It is the same element, just a different version of it.
The element doesn’t change because they have the same atomic number

16. How can you tell one isotope from another?
Although isotopes share most of the same physical and chemical properties, Isotopes of the same element have different mass numbers.
Atomic Mass = protons + neutrons
Protons and Neutrons have a mass of about 1 atomic mass unit (amu)
Electrons have such a small mass they are considered to be 0 amu

17. Parts of the Atom Charge Mass (amu) Location Proton + 1
1 (very large!)
nucleus
Neutron
Electron
- 1
.0005 (very very small!)
outside nucleus
Parts of the Atom

18. What’s the difference? Why are they different?
Atomic Mass
The total mass of one atom of an element
Because elements have isotopes, the atomic mass listed on the periodic table is a weighted average of all the naturally occurring isotopes of an element.

19. Atomic Mass and Isotopes
There is a lot more Hydrogen-1 than Hydrogen-2 so Hydrogen-1 is weighted more heavily when calculating the atomic mass of hydrogen.
Mass: ______ Mass: ______ Mass: ______