Atomic Structure 8 th Grade Science. Parts of an Atom Protons = positive charge 1+ Neutrons = do not have a charge (0) Electrons = negative charge 1-

Atomic Structure

8th Grade Science

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!

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

All atoms have 2 common structures:

nucleus

energy level(s)

energy level

nucleus

electrons

+

+

protons

neutrons

-

-

Each structure is made of subparticles.

Energy Levels

• 1st shell can hold 2 electrons

• 2nd shell can hold 8• 3rd shell can hold 18

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.

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.

400 BC Democritus 1904 Thomson

1911 Rutherford

1913 Bohr

Present Electron Cloud1926

If both protons and neutrons are found in the nucleus, why is it positive?

A. Neutrons have a positive charge

B. Both neutrons and protons have a positive charge

C. Protons have a positive charge and neutrons have no charge

D. Neutrons have a negative charge

Atomic Structure VideoDiscovery Education

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.

How many protons are in Magnesium?

A. 25

B. 24.31

C. 11

D. 12

What is the atomic mass of Potassium?

A. 39.10

B. 19

C. 15

D. 30.97

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

A Little Saying to help you remember…

A

P

E

M

A

N

Atomic Number =

Atomic Mass =

Protons =

Neutrons =

Electrons =

Energy Levels =

++

+

++

+ ++

8

8

8

16

8

2oxygen atom

+

What is the number of neutrons in Potassium?

A. 39

B. 19

C.20

D.21

How many neutrons are in Lithium?

A. 3

B. 4

C.6

D.7

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.

http://www.tutorvista.com/content/science/science-i/structure-atom/valence-shell-electron.php

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

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.