Atomic Structure
The Atoms Family
• Atom: the smallest
part of an element.
Name means
“indivisible”
Who’s atom is it?
Dalton
(bb)
Electron
cloud model
Thompson
(Plum Pudding)
Standard
Model
Rutherford
Bohr
(planetary)
Parts of an Atom
• Nucleus:The main
center of an atom.
Made up of
protons and
neutrons
• Proton:In the
nucleus. Has a +
charge. Atomic
number tells the
number of protons
• Neutron:In the
nucleus. Has NO
charge. Is there to
keep protons apart
Parts of an ATOM
 Electrons: In the electron cloud, has a
negative charge.
The Same, But Different
• Isotopes:An element with different
numbers of neutrons.
•
• Atomic mass - atomic number = number of
• neutrons.
• Example: Hydrogen 3
3(mass) - 1 (atomic #) =
2 neutrons
• Having an unequal number of neutrons and
protons can make an atom unstable!
B. Subatomic Particles
ATOM
ATOM
NUCLEUS
NUCLEUS
ELECTRONS
ELECTRONS
PROTONS
PROTONS
NEUTRONS
NEUTRONS
POSITIVE
CHARGE
NEUTRAL
CHARGE
Most of the atom’s mass.
NEGATIVE
CHARGE
NEGATIVE CHARGE
Atomic Number
equals the # of...
Let’s review
• Name the two sub-atomic particles found in
the nucleus of an atom:
Proton and Neutron
• What is the charge of a proton?
Positive
• What is the charge of a neutron?
No charge (neutral)
• Where are the electrons at?
Orbiting the nucleus
Atomic Structure
II. Electron Cloud Model
 Orbital
 Energy Levels
 Bohr Model Diagrams
Niels Bohr  Bright-Line Spectrum
(1913)
• tried to explain
presence of specific
colors in hydrogen’s
spectrum
 Energy Levels
• electrons can only
exist in specific
energy states
 Planetary Model
Demonstration Time
Niels Bohr (1913)
Bright-line spectrum
 Planetary Model:
• electrons move in
circular orbits within
specific energy levels
electron shells
a) Electrons different amounts of energy
and at different energy levels or
electron shells.
b) Electron shells (levels) determine…
how an atom behaves when it
encounters other atoms
Levels
• 1st Level: closest to nucleus. Has 1 orbital. Can
hold 2 electrons
• 2nd level: next one out. Has 2 orbitals. Can hold 8
electrons.
• 3rd level: Holds 8 electrons.
• 4th level: Holds 18 electrons
Why are electrons
important?
1) Elements have different electron
configurations so different levels of
bonding
2) Valence electrons are the electrons in
the outer most shell.
3) Valence electrons are important
because they affect how the element
reacts with other elements.
How many valence electrons
are in these different atoms?
Octet Rule = atoms tend to gain, lose or share electrons so as to have
8 electrons
C would like to
N would like to
O would like to
Gain 4 electrons
Gain 3 electrons
Gain 2 electrons
C. Stability
 Octet Rule
• most atoms form bonds in order to
have 8 valence e• full outer energy level
Ne
• like the Noble Gases!
 Stability is the driving force behind bond
formation!
Electron Dot Structures
Symbols of atoms with dots to represent the
valence-shell electrons
1
2
13
14
15
16
17
H
Li
18
He:



Be
B 


C


Na Mg


Al


N


 Si 


O



P
S




: F  :Ne :




:Cl  :Ar :


Learning Check

A.
X would be the electron dot formula for
1) Na
B.

 X 

1) B
2) K
3) Al
would be the electron dot formula
2) N
3) P
Stability
 Why is it important for an atom to be
“stable”?
• So it is less reactive.
 Why are noble gases stable?
• They have a full energy level.