THE ATOM
THE ATOM
 The atom has
three parts:
1) Protons
2) Neutrons
3) Electrons
PROTONS
 Protons:
1) Found in the nucleus
2) Mass: one (1) Atomic Mass Unit
3) have a (+) positive charge,
1 PROTON = 1 POSITIVE Charge
PROTONS (CONT’D)
 On the periodic table, each element is numbered. This number equals the
number of Protons in the nucleus.
NEUTRONS
 Also found in the nucleus.
 Mass: one (1) Atomic Mass Unit.
 They have NO charge. Neutron = Neutral
ELECTRONS
 Found around the nucleus (like planets around
the Sun)
 An Electron’s mass is almost nothing…almost
 Have a negative (-) charge
ELECTRONS = NEGATIVE
https://www.youtube.com/watch?v=hhbqIJZ8wCM
STANDARD ATOMIC
NOTATION
9
Be
4
Mass Number = mass of all the
protons and neutrons in the nucleus
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
 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!
 Have your periodic table ready
 How many protons, neutrons and electrons in one atom of:
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
 Named after the work done by Neils Bohr and
Ernest Rutherford
 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?
ELECTRON SHELLS
Second Shell,
Maximum 8 electrons
3
1
4
2
7
Nucleus
10
12 P
12 N
6
5
8
9
WHY 8 IN THE SECOND SHELL??
8 elements in second period
ELECTRON SHELLS
Third shell, max # 8 electrons
11
12
3
4
1
2
7
10
5
Nucleus
12 P
12 N
Note: Magnesium only
needs 2 electrons in
this shell because it
has 12 total
6
9
8
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
 82 protons = element 82 which is LEAD
THE NOBLE GASES
4
3
1
1
2
2
7
Nucleus
2P
2N
10
5
Nucleus
10 P
10 N
6
8
9
 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
1
2
7
5
Nucleus
12 P
12 N
10
2
Nucleus
10
8
5
7
10 P
10 N
6
6
9
Magnesium
9
Neon
8
SO, HOW WOULD MAGNESIUM LOOK LIKE NEON??
3
 So, if Mg lost two
Electrons, but still had
the same number of
Protons, what is its
Charge?
 +2
1
4
2
5
7
10
Nucleus
12 P
12 N
6
9
8
CHARGES
 The outer electrons on an atom are called:Valence electrons.
 Atoms want a Bohr-Rutherford Diagram that look like the
Noble Gases because…
 have the most stable structure
 Won’t react when mixed
 Usually, this means the atom ends up with a Charge.
FLUORINE
4
3
1
2
7
10
5
Nucleus
9P
9N
6
8
9
 What does F need to look like a Noble gas?
 If we add one Electron, what will the Charge of the atom be?
-1
IONS
3
4
1
2
5
7
Nucleus
10
8
12 P
12 N
9
6
 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
GROUPS
11
12
3
4
3
1
2
1
5
7
10
4
Nucleus
12 P
12 N
6
8
2
Nucleus
4P
4N
9
Mg
Be (Berylium)
SO…
 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