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Atomic Structure
Chapter 4.1
Pages 70-76
Atomic Theory
Every element is made of tiny, unique
particles called atoms that cannot be
subdivided.
 Atoms of the same element are
exactly alike.
 Atoms of different elements can join
to form molecules.

Parts of the Atom


Nucleus
 Dense center of the atom
Subatomic particles
 Proton
 Neutron
 Electron
Proton
Has a +1 charge
 Mass of 1.67 x 10-27 kg
 Located inside the nucleus

Neutron
Has no charge
 Mass of 1.67 x 10-27 kg
 Located inside the nucleus

Electron
Has a negative charge
 Mass of 9.11 x 10-31 kg
 Moving around outside the nucleus.

Charge of an Atom



Atoms are neutral
The positive protons and negative electrons
cancel each other out.
Nucleus has a positive charge because it
contains protons.
How do we know find out about
the atom
Everything we need to find out about the
subatomic particles in the atom is on the
Periodic Table
How do we know the number
of subatomic particles in an
atom?


Atomic number: this number indicates the
number of protons in an atom
The atomic # for any given element NEVER
changes

Ex: Hydrogen’s atomic number is 1


So hydrogen has 1 proton
Ex: Carbon’s atomic number is 6

So carbon has 6 protons
**The number of protons identifies the
atom.
Ex. 2 protons = ?, 29 protons = ?
Atomic Number on the
Periodic Table
Atomic Number
Symbol
11
Na
LecturePLUS Timberlake
10
How do we know the number
of subatomic particles in an
atom?

Mass number: the number of protons and
neutrons in the nucleus
Protons + Neutrons = Mass Number

Ex: Find the mass of Lithium (Li)
Atomic Mass
Determining the number of
protons and neutrons

Li has a mass number of 7 and an atomic
number of 3




Protons = 3 (same as atomic #)
Mass # - Atomic # = Neutrons
Neutrons= 7-3 = 4
Ne has a mass number of 20 and an atomic
number of 10


Protons = 10
Neutrons = 20 - 10= 10
Isotopes

Atoms with the same number of protons,
but different numbers of neutrons.

Atoms of the same element (same atomic
number) with different mass numbers
Isotopes of chlorine
35Cl
37Cl
17
17
chlorine - 35
chlorine - 37
LecturePLUS Timberlake
14
ions
If protons ≠ electrons the atom is called an “ion”
Protons
-- Electrons
Charge of the atom
If protons > electrons : positive charge
If protons < electrons : negative charge
Energy Levels



Electrons can be located in a specific energy
level
Gain energy to move to a higher energy level.
Lose energy to move to a lower energy level.
Energy Levels
1st Level – contains 2 e 2nd Level – contains 8 e 3rd Level – contains 18 e 4th Level – contains 32 e 5th to 7th Level – contains 32 e- each

Sublevels
1st level has 1 sublevel
 2nd level has 2 sublevels
 3rd level has 3 sublevels
 4th level has 4 sublevels

Orbitals
s orbital – holds 2 e p orbital – holds 6 e d orbital – holds 10 e f orbital – holds 14 e
s orbital

Can hold a
maximum of 2
electrons
p orbital

Each p orbital can hold 2 electrons. All
three can hold a maximum of 6
electrons.