1. Atomic Structure
8th Grade Science

2. Parts of an Atom Protons = positive charge 1+
Neutrons = do not have a charge (0)
Electrons = negative charge 1-
Atoms of different elements differ in the number of protons they contain.
Atomic Number = number of protons and number of electrons in a neutral atom Identifies the element!

3. A little joke…
A neutron walked into a restaurant and asked how much for a drink. 
The bartender replied,  "for you, no charge." 
-Jaime - Internet Chemistry Jokes

4. All atoms have 2 common structures:
nucleus
energy level(s)

5. - - Each structure is made of subparticles. + energy level protons
nucleus
electrons
neutrons -

6. Energy Levels 1st shell can hold 2 electrons 2nd shell can hold 8
3rd shell can hold 18

7. Electron Cloud
Protons and Neutrons are found in a small, positively charged (+) center of the atom called the nucleus that is surrounded by a cloud containing electrons.

8. Atomic Mass Unit (AMU):
The mass of a proton or neutron is about 1 atomic mass unit or AMU
Proton = 2000 times larger than an electron.
The electron cloud makes most of an atom’s volume (space). Electrons are very tiny.
A neutron is large and heavy like a proton.

9. Present Electron Cloud
400 BC Democritus
1904 Thomson
1913 Bohr
Present Electron Cloud
1911 Rutherford
1926

10. If both protons and neutrons are found in the nucleus, why is it positive?
Neutrons have a positive charge
Both neutrons and protons have a positive charge
Protons have a positive charge and neutrons have no charge
Neutrons have a negative charge

11. Atomic Structure Video Discovery Education

12. Carbon has 6 protons. The atomic number of carbon is 6.
The number of protons in the nucleus of an atom is that atom’s atomic number. + -
Carbon has 6 protons. The atomic number of carbon is 6.
The number of protons plus the number of neutrons in the nucleus of an atom is its atomic mass.

13. How many protons are in Magnesium?25
24.31 11 12

14. What is the atomic mass of Potassium?
39.10 19 15
30.97

15. 16 Atomic mass (protons + neutrons) - 8 Atomic number (protons) ___
To find the number of neutrons in an atom, subtract the atomic number from the atomic mass.
16 Atomic mass (protons + neutrons)
- 8 Atomic number (protons)
___
8 Number of neutrons

16. A Little Saying to help you remember…
tomic # =
ass #
rotons =
tomic #
lectrons
uetrons

17. Atomic Number = 8 8 Protons = 16 Atomic Mass = Neutrons = 8 2+ + + + + + + + +
Neutrons = 8
Energy Levels = 2
oxygen atom
Electrons = 8

18. What is the number of neutrons in Potassium?39 19 20 21

19. How many neutrons are in Lithium?3 4 6 7

20. Valence Electrons
Electrons farthest away from the nucleus or most loosely held.
Ranges from 1 to 8 valence electrons
Many properties of the atom, and therefore of an element, are determined by the number of valence electrons.

21. Electron Dot Diagrams Also called Lewis Structure
Used to represent valence electrons
Made up of the element symbol surrounded by dots
Each dot stands for one valence electron

22. Chemical Bonds
Valence electrons can form chemical bonds, a force that holds atoms together.
When bonds form, valence electrons are either transferred or shared between atoms.
When atoms end up with 8 or 0 valence electrons, they become more stable – or less reactive.