The Atom
The Atom
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The atom has
three parts:
Protons
2) Neutrons
3) Electrons
1)
Protons
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1)
2)
3)
Protons:
Found in the nucleus
Mass: one (1) Atomic Mass Unit
have a (+) positive charge,
1 PROTON = 1 POSITIVE Charge
Protons (Cont’d)
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On the periodic table, each element is
numbered. This number equals the number of
Protons in the nucleus.
Neutrons
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Also found in the nucleus.
Mass: one (1) Atomic Mass Unit.
They have NO charge. Neutron = Neutral
Electrons
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Found around the nucleus (like planets around the Sun)
An Electron’s mass is almost nothing…almost
Have a negative (-) charge
ELECTRONS = NEGATIVE
Standard Atomic Notation
Mass Number = mass of all the
protons and neutrons in the nucleus
9
Be
4
Element Symbol – eg. Beryllium
Atomic Number = number of protons
in the nucleus and the number of
electrons orbiting the nucleus
To find the number of neutrons in the nucleus, subtract atomic
number from mass number. There would be 9 – 4 or 5 neutrons
in a Beryllium atom
Remember
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The periodic table is organized by atomic
number (the number of protons the
element has in its nucleus)
Protons are + and electrons are The number of protons = the number of
electrons (positives = negatives)
Let’s try some!
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Have your periodic table ready
How many protons, neutrons and
electrons in one atom of:
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Hydrogen?
Carbon?
Beryllium?
Calcium?
Fluorine?
1 p+, 1 e-, 0 n
6 p+, 6 e-, 6 n
4 p+, 4 e-, 5 n
20 p+, 20 e-, 20 n
9 p+, 9 e-, 10 n
Bohr-Rutherford Diagrams
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Named after the work
done by Neils Bohr and
Ernest Rutherford
(nobody before them
gets any respect!)
Flattened model of the
inside of an atom
Unique for each atom
Electron Shells
First Shell, maximum 2
electrons
1
2
Nucleus
12 P
12 N
Why only 2 in the first shell?
2 elements in first row (period)
Electron Shells
Second Shell,
Maximum 8 electrons
3
4
1
2
5
7
10
8
Nucleus
12 P
12 N
9
6
Why 8 in the second shell?
8 elements in second period
Electron Shells
Third shell, max # 8 electrons
11
12
3
4
1
2
5
7
10
Nucleus
8
12 P
12 N
Note: Magnesium only needs 2 electrons in this shell because it has 12
total
9
6
Bohr-Rutherford Diagrams
Eg. Magnesium
11
12
3
4
1
2
5
7
10
8
Nucleus
12 P
12 N
9
6
Guess this element
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82 protons = element 82 which is LEAD
The Noble Gases
3
1
1
2
Nucleus
2P
2N
4
7
10
2
Nucleus
10 P
10 N
9
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5
8
6
Column to the far right of the periodic table, He,
Ne, Ar, Kr, Xe, & Rn
So, how would Magnesium look
like Neon?
11
12
4
3
3
4
1
2
1
5
7
7
Nucleus
10
8
10
2
5
Nucleus
10 P
10 N
8
12 P
12 N
9
9
6
6
Magnesium
Neon
3
4
1
2
5
7
Nucleus
10
9
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8
12 P
12 N
6
So, if Mg lost two Electrons, but still had the
same number of Protons, what is its Charge?
+2
Charges
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The outer electrons on an atom are called:
Valence electrons.
Atoms want a Bohr-Rutherford Diagram
that look like the Noble Gases because…
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have the most stable structure
Won’t react when mixed
Usually, this means the atom ends up with
a Charge.
Fluorine
3
4
1
2
5
7
Nucleus
9P
9N
10
9
8
6
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What does F need to look like a Noble gas?
If we add one Electron, what will the Charge of
the atom be?
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-1
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Ions
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Ion= a Charged atom in which the number of
ELECTRONS (-) is different from the number of
PROTONS (+).
Ionic Charge= is the number of positive (+) or
negative (-) Charges on an atom. Ex: Mg+2
3
4
1
2
5
7
Nucleus
10
12 P
12 N
9
6
8
Groups
12
11
3
3
4
4
1
1
2
5
7
Nucleus
10
2
8
12 P
12 N
9
Mg
Nucleus
4P
4N
6
Be (Berylium)
So…
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Even though each element has a different
# of PROTONS and ELECTRONS, each
element in a group has a similar BohrRutherford Diagram
This means they want to gain or lose the
same number of Electrons.
It also means elements in a Group will
react similarly in Chemical Reactions