Atomic Structure
Nucleus = small, positively charged center of an atom.
- contains all the mass of the atom!
Composed of 2 particles:
- mass of 1.673 x 10-24 g = 1 amu (atomic mass unit)
2) Neutron = neutral, no charge.
- 1 amu
Atomic Number = number of protons in the nucleus of an atom.
- identity of the element!
Ex:
Li
3
Atomic Number
Mass Number = # of protons + # of neutrons in a single atom.
- ALWAYS a whole number!
Ex:
Li
3
7
Mass Number
Atomic Number
Protons =
Neutrons =
Mass Number =
- NOT on the periodic table!
3
4
7
= 7 - 3
Isotope = atoms of the same element with different numbers of neutrons.
Ex: Carbon
~95%
C
12
6
BUT
~5%
C
14
6
Protons =
Neutrons =
Protons =
Neutrons =
6
6
= 12 - 6
6
8
= 14 - 6
Electrons = negatively charged particle.
- mass = amu … basically no mass!
- Charge = # of positive (+) protons + charge of negative (-) # of electrons.
Ex:
Li
3
7
Mass Number
Atomic Number
Charge
If there is nothing in the “charge position”, the atom has 0 charge = neutral!!!
Protons =
Neutrons =
Electrons =
3
4
3
# of protons = # of electrons when neutral!!!
= 7 - 3
X
Ex:
Mg
12
24
+2
Protons =
Neutrons =
Electrons =
Cl
17
36
-1
Protons =
Neutrons =
Electrons =
12
12
10
Two fewer electrons than protons.
17
19
18
One more electron than protons.
= 24 - 12
= 36 - 17
Ex:
Na
24
Protons =
Neutrons =
Electrons = 10
S
Protons =
Neutrons = 16
Electrons = 18
11
13
One fewer electron than protons.
11
+1
16
32
16
Two more electrons than protons.
-2