Subatomic Particles
1. Subatomic Particles
Particle
Electrons
Symbol
(table O)
e
0e
-1
0β
-1
Charge
Mass
(amu)
Location
Negative
(-1)
1/1872 amu
0 amu
Outside
nucleus
(energy
levels)
Protons
p
1p
1
1H
1
Positive (+1) 1 amu
Nucleus
Neutrons
n
1n
0
Neutral
(0)
Nucleus
1 amu
Special notes on subatomic particles
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In a neutral atom # of protons=#of electrons.
Atoms are electrically neutral.
If the number of protons does not equal the number
of electrons you have a charged atom known as an
ion.
# protons > # electrons forms a + ion (cation)
# electrons > # protons forms a – ion (anion)
The charge on the nucleus is positive.
Most of the mass of an atom is in nucleus.
2. Atomic Number (z)
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1913—Henry Mosley
Used to identify an atom
Indicates the number of protons
In a neutral atoms also gives the number of
electrons
Also called the Nuclear Charge
3. Mass Number (A)
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Total number of protons and neutrons in the
nucleus of an atom. (nucleons)
Notation: AXZ
Mass # = #protons + # neutrons
# neutrons = Mass # - # protons
Try the following:
Sample Atom
Notation
Protons
(atomic #)
Neutrons
(mass #atomic #)
Electrons(sa
me as
atomic#)
Carbon-12
C-12
12C
6
6
12-6=6
6
Chlorine-35
Cl-35
35Cl
17
17
35-17=18
17
Chlorine-37
Cl-37
37Cl
17
17
37-17=20
17
Neon-20 Ne20
20Ne
10
10
20-10=10
10
Oxygen-16 O16
Determine the # of protons, neutrons,
and electrons for these added
examples:
 19F9
 9 protons
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19-9=10 neutrons
9 electrons
 19F9-1
 9 protons
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10 neutrons
10 electrons
 24Mg12
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12 protons
24-12=12 neutrons
12 electrons
 24Mg12+2
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12 protons
12 neutrons
10 electrons
4. Isotopes
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Thomson (1912) found 2 types of neon atoms and
Soddy (1910) found 2 types of uranium atoms.
2 elements that have the same atomic number but
different mass numbers
Based on atomic structure: 2 elements that have
the same number of protons but different number of
neutrons.
For example: Cl-35 and Cl-37
5. Atomic Mass
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Decimal number
Average of all the naturally occurring
isotopes for a particular element
If you round the atomic mass it gives you the
mass number for the most common isotope.
Unit is amu (atomic mass unit)
1 amu is 1/12 the mass of C-12
Gram atomic mass= amu but in grams
Try the following:
1.
Determine the number of protons, neutrons,
and electrons for the following isotopes of
hydrogen:
Solution:
Hydrogen-1 (protium) 1H1
Hydrogen-2 (deuterium) 2H1
Hydrogen-3 (tritium) 3H1
1p,0n,1e
1p,1n,1e
1p,2n,1e
2.
Naturally occurring chlorine consists of
75% Cl-35 and 25% Cl-37. Find the
average atomic mass.
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.75(35) + .25(37)= 35.50 amu or
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75(35) + 25(37) =35.50 amu
100
3. Calculate the atomic mass of an element with
isotope A occurring 70.0% of the time with a mass
of 13.0 amu and isotope B occurring 30.0% of the
time with a mass of 15.0 amu.

.70 (13.0) +.30 (15.0) =13.6 amu
4.
An element X has three isotopes
X-30 has a 50.0% abundance, X-28 has a 30.0%
abundance and X-31 has a 20.0% abundance.

.500(30) + .300(28) + .200 (31) = 29.6 amu
5. There are two isotopes of element Z, 60.0% of the
atoms have a mass of 58.0 amu and 40.0% have a
mass of 57.0 amu. Calculate theatomic mass of
element Z.

.600(58.0) + .400(57) = 57.6 amu