The Atom &
Subatomic Particles
What we knew by 1932:
electron
proton
Relative Charge
Relative Mass
0e
-1
0.0005486 amu
(or 0 amu)
or 1H
+1
1.0073 amu
(or 1 amu)
0
1.0087 amu
(or 1 amu)
-1
1p
1
neutron
1
1n
0
Location of Subatomic Particles
• electrons located outside nucleus
• protons & neutrons located inside nucleus
Atomic Number
 atomic


number:
= size of nuclear charge
= number of protons in nucleus
determines identity of element
gives order to PT
 For
neutral atoms:
atomic number = # protons = # electrons
Mass Number
=
# protons
+
# neutrons
Isotopes
atoms of same element can have different
mass numbers

# protons must be the same so …
# neutrons must be different
Dalton’s theory must be modified:


the atom is divisible
presence of subatomic particles
atoms of same element can be different
isotopes have different # neutrons
Notation
12C
6
•left superscript is mass number
•left subscript is atomic number
Notation
12C
6
12 = # protons + neutrons
6 = # protons
How many neutrons in this
atom?
12 – 6 = 6 neutrons
17O
8
Mass number is ?
Atomic number is ?
17
8
# of neutrons is ? 17 – 8
# of electrons in atom is?
=
8
9
15
7
N
Mass number is ?
15
Atomic number is ? 7
# of neutrons is ? 15 – 7
=8
# of electrons in atom is? 7
19
F
Mass number is ? 19
Atomic number is ? 9
# of neutrons is ? 19 – 9 = 10
# of electrons in atom is? 9
Other Notations
C-12
# after symbol is mass number!
must
look up atomic number
What’s the difference between
H-1, H-2, and H-3?

All H’s have 1 proton
H-1: mass # = 1
1 proton, ? neutrons
0
H-2: mass # = 2
1 proton, so it must have ?
H-3: neutrons
mass # = 3
1 proton, so it must have ? neutrons
1
2
Consider U-234, U-235, & U-238
 What’s
the atomic number of U? 92
 How many protons in U? 92
 How many neutrons in U-234? 234 – 92 = 142
 How many neutrons in U-235? 235 – 92 = 143
 How many neutrons in U-238? 238 – 92 = 146
 How many electrons in U? 92
How many neutrons in Po-217?
 What’s
 How
 So
the atomic number?
many protons?
84
the neutrons are …
217 – 84 = 133 neutrons!
84
IONS
IONS = atoms that gained or lost electrons
 protons
and electrons aren't = anymore, so
ions are not neutral they carry a charge (+/-)
IONS
 Charge
of ion:
= # protons minus # electrons
(subtract the electrons since are negative)
IONS
 If
atom loses electrons, it has more (+)
protons than (-) electrons
 What kind of ion is it?
positive
 If
atom gains electrons, it has more (-)
electrons than (+) protons
negative
 What kind of ion is it?
Charge of Ions

Ion charge: right superscript
Cl-1 a chloride ion with a charge of -1
Na+1
a sodium ion with a charge of +1
O-2 an oxygen ion with a charge of -2
If no right superscript, it’s understood to be zero and
therefore a neutral atom
Putting it all together
 How
many protons, neutrons, & electrons
in each of the following
23Na+1
1
Lost 1
e-
11 p, 12 n, 10 e
34S-2
16
Got 2
e-
16 p, 18 n, 18 e
Lost 2
64Zn+2 Lost 2
30
ee12 p, 13 n, 10 e 30 p, 34 n, 28 e
25Mg+2
12
Got 1
e9 p, 10 n, 10 e
19F-1
9
Got 3
e7 p, 6 n, 10 e
13N-3
7
What is an amu?
atomic mass unit
amu  1/12 the mass of the C-12 atom