Atomic Structure
The atom as we understand it
today
Atomic Structure
The atom consists of 3 subatomic particles?
Do you know what they are?
Proton
Electron
Neutron
Atomic Structure
The following notation is used:
A
X
Z
A = Mass Number
Z = Atomic Number
Atomic Structure
Atomic Number (Z) – this is unique to each atom.
The atomic number is equal to the number of
protons.
Mass Number (A) – this is the total mass of each
atom. Remember, each P and N has a mass of
about 1amu.
amu = 1/12 the mass of a C-12 atom
Therefore, the mass number = #P + #N
Atomic Structure
The atom written as 3617Cl can also be
expressed as Cl-36.
The 17 is understood, because we are
referring to the chlorine atom.
The 36 refers to the Mass Number.
Atomic Structure
Element
C-12
F-14
N-14
Na-25
Li-8
Atomic #
Make the following grid
in your notes:
Mass #
#P
#N
#e
Atomic Structure
Element
Protons
119
Make the following grid
in your notes:
238
50Sn
92U
17
85
Neutrons
92
Electrons
82
Atomic Number
Mass Number
36
92
92
235
Atomic Structure
Can we have both U-235 and U-238?
Yes! They are referred to as Isotopes.
Isotopes are atoms of the same element
(they have the same number of P) but they contain
a different number of Neutrons. (This is what
changes the mass number)
Atomic Structure
Now what do we do when we are given:
60 Co2+
27
We now have:
P: 27
N:33
e-: 25 (We have two fewer electrons than P)
Atomic Structure
***WARNING***
Never change the number of protons when a
charge is present, ALWAYS change the
number of e-.
A positive charge (More P than e-)
A negative charge (More e- than P)
Atomic Structure
Element
Protons
25
Make the following grid
in your notes:
2+
126
12Mg
85
18
26
28
Atomic Number
Mass Number
3+
17
Neutrons
Electrons
51Sb
36
10
51
13
27