Atomic Structure

Back to chemistry page

Description: Description: \\mms04\Intranet\staff\hand\atombgclr.gif

THE ATOM IS MOSTLY OPEN SPACE!

The Nucleus: In 1911, Ernest Rutherford said that the nucleus was in the center of the atom. He said that the atom is mostly open space. If the nucleus were 2 cm in diameter, the nearest nucleus of an adjacent atom would be 400 meters away. Thus lead is empty space at the atomic level!

Subatomic Particles: Protons, neutrons and electrons are subatomic particles. In other words, they are particles that are smaller than the atom.

Protons, found in the nucleus, are positive. Protons determine what atom is. Atoms with 2 protons in the nucleus are Helium atoms. Atoms with 6 protons in the nucleus are Carbon atoms. Atoms with 92 protons are Uranium atoms.

James Chadwick identified neutrons 20 years later. Neutrons are neutral and hold the nucleus together. Neutrons are heavier than protons.

 

To determine the number of neutrons in an element, simply subtract the number of protons from the atomic mass. For example:

The Atomic Mass of Aluminum         = 27

The number of protons in Aluminum = 13

 

27- 13 = 14 Neutrons in Aluminum

 

Element

Protons

Mass

Neutrons

H

1

1

0

He

2

4

2

Li

3

7

4

Be

4

9

5

B

5

11

6

C

6

12

6

N

7

14

7

O

8

16

8

F

9

19

10

Ne

10

20

10

Na

11

23

12

Mg

12

24

12

Al

13

27

14

Si

14

28

14

P

15

31

16

S

16

32

16

Cl

17

35

18

Ar

18

40

22

K

19

39

20

Ca

20

40

20

 

2 atoms with the same number of protons, but different numbers of neutrons are called isotopes. The atoms differ only in mass. Isotopes are used in the medical field:

Technetium 99- injected in body and scanned.

Cobalt 60 is used for treating cancer.

Description: Description: \\mms04\Intranet\staff\hand\line3.gif

Electrons are negative and fly around the outside of the atom. They have hardly any mass. In fact, the mass of 1 proton = the mass of 1837 electrons.

2 electrons fill the first level, ring, or shell. How many electrons can hydrogen hold? Description: Description: \\mms04\Intranet\staff\hand\Hydrogen.gif

8 electrons fill the second level, ring, or shell.

8 fill the third. Actually, 18 electrons will fill it. However, you will not see this until high school.

Here are a few examples of the rings of atoms:

The number of valence electrons is not responsible for identifying atoms because electrons readily come and go. When it comes to bonding, valence electrons are the ones that matter. 

Try this atom builder!

Back to chemistry page