Atomic
Structure
Mr. Matthew Totaro
Legacy High School
Chemistry
1
Experiencing Atoms
• Atoms are incredibly small, yet they compose
everything.
• Atoms are the pieces of elements.
• Properties of the atoms determine the
properties of the elements.
2
Experiencing Atoms
• There are about 91 elements found in
nature.
Over 20 have been made in laboratories.
• Each has its own, unique kind of atom.
They have different structures.
Therefore they have different properties.
3
The Nuclear Atomic Model
4
Atomic Theory from 1800-1911
5
The Modern Atom
• Atoms are composed of
three main pieces:
Protons (+), Neutrons
(neutral), and Electrons (-).
• The nucleus contains
protons and neutrons.
• The electrons move outside
the nucleus
 The radius of the atom is about 105
times larger than the radius of the
nucleus.
6
Subatomic Particles
• Protons and electrons are the only particles that
have a charge.
• Protons and neutrons have essentially the same
mass.
• The mass of an electron is so small we ignore it.
7
The Sub-Atomic Particles
Subatomic
Mass
Mass
Location Charge Symbol
Particle
g
amu
in atom
Proton
1.67262 1.00727
nucleus
+1
p+
empty
-1
e-
0
n0
x 10-24
Electron
0.00091 0.00055
x 10-24
Neutron
1.67493 1.00866
space
nucleus
x 10-24
8
Elements
• Each element has a unique name and symbol.
 The symbol is either one or two letters
 One capital letter or one capital letter + one lower case letter.
H = Hydrogen = “water-former”
Br = Bromine = ‘stench’
Liquid Bromine
9
Atomic number = number of protons in nucleus
Mass number = number of protons + number of neutrons
= atomic number + number of neutrons
10
2.3
Example 2.3b How many protons, electrons,
52
and neutrons are in an atom of 24 Cr ?
Given:
Find:
Concept Plan:
52
24 Cr
therefore A = 52, Z = 24
# p+, # e-, # n0
symbol
symbol
Relationships:
Solution:
Check:
atomic
number
atomic & mass
numbers
# p+
# e-
# n0
in neutral atom, # p+ = # emass number = # p+ + # n0
Z = 24 = # p+
# e- = # p+ = 24
A = Z + # n0
52 = 24 + # n0
28 = # n0
for most stable isotopes, n0 > p+
11
Isotopes:
• Atoms of the same element with different masses.
• Isotopes have different numbers of neutrons.
12
Ions
Cation – ion with a positive charge
-When a neutral atom loses one or more electrons
Na
11 protons
11 electrons
Na+
11 protons
10 electrons
Anion – ion with a negative charge
-When a neutral atom gains one or more electrons
Cl
17 protons
17 electrons
Cl-
17 protons
18 electrons
13
2.5
Do You Understand Ions?
How many p+, n0, and electrons are in?
27 Al 3+
13
13 protons, 10 (13 – 3) electrons, 14 neutrons
How many p+, n0, and electrons are in?
78 Se 234
34 protons, 36 (34 + 2) electrons, 44 neutrons
14
2.5
Review
•
•
•
•
•
What is the atomic number of boron, B?
What is the atomic mass of silicon, Si?
How many protons does a chlorine atom have?
How many electrons does a neutral neon atom have?
Will an atom with 6 protons, 6 neutrons, and 6 electrons
be electrically neutral?
• Will an atom with 27 protons, 32 neutrons, and 27
electrons be electrically neutral?
• Will an Na atom with 10 electrons be electrically
neutral?
15
Review
•
•
•
•
•
What is the atomic number of boron, B? 5
What is the atomic mass of silicon, Si? 28.09 amu
How many protons does a chlorine atom have? 17
How many electrons does a neutral neon atom have? 10
Will an atom with 6 protons, 6 neutrons and 6 electrons
be electrically neutral? Yes
• Will an atom with 27 protons, 32 neutrons, and 27
electrons be electrically neutral? Yes
• Will an Na atom with 10 electrons be electrically
neutral? No
16