# Atomic Structure by kASYpW

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• pg 1
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THE STRUCTURE OF AN
ATOM
Atomic Structure
• Atoms are composed of 2 regions:
• Nucleus: center of atom that contains mass
of atom
• Electron cloud: region that surrounds
nucleus that contains most of space in atom

Nucleus
Electron
Cloud
What’s in the Nucleus?
• Nucleus contains 2 of 3 subatomic
particles:
• Protons: subatomic particle w/ 1+ charge (p+)
• Rutherford - 1911
• Neutrons: subatomic particle w/ no charge
(no)
• James Chadwick - 1932
What’s in the Electron Cloud?
• The 3rd subatomic particle resides
outside nucleus in electron cloud
• Electron: subatomic particle w/ 1- charge
(e-) and virtually no mass
• JJ Thomson - 1897
How do these particles interact?
• Protons and neutrons live compacted in tiny
nucleus
• most atom’s mass
• electrons small and reside outside nucleus
• small mass (2000 e- = 1 p+ or no)
• occupy large volume of space outside nucleus

Atoms
How do the subatomic particles balance
each other?
• In atoms:
• protons = electrons
• If 20 protons are present in atom then 20
electrons balance overall charge of atom—atoms
are neutral
• The neutrons have no charge; therefore they
do not need to (and often times don’t) equal
protons or electrons
How do we know the number of
subatomic particles in an atom?
• Atomic #: indicates # of protons in
atom
• Ex: Hydrogen’s atomic # is 1
• hydrogen has 1 proton
• Ex: Carbon’s atomic # is 6
• carbon has 6 protons
**Number of protons identifies element
similar to how your fingerprint ID’s you.
Ex. 2 protons = He, 29 protons = Cu
ALWAYS!!
How do we know the number of
subatomic particles in an atom?
• Mass number: number of protons and
neutrons in nucleus (p+ + no)
• Ex: hydrogen can have a mass # of 3.
Since it has 1 proton it must have 2 neutrons

• # of neutrons = mass # - atomic #
What are Isotopes?
• Atoms of same element with different #
of neutrons
• Same atomic #
• Different mass # (b/c neutrons are
different)
• Ex. Carbon 12, Carbon 13, and Carbon 14 all
naturally occurring isotopes of Carbon.
• Each has 6 p+ and 6 e-, but each has
different # of neutrons (therefore,
different mass#)
Determining the number of protons and
neutrons
• Li has mass # of 7 and atomic # of 3
• Protons = 3 (same as atomic #)
• Neutrons= 7-3 = 4 (mass # - atomic #)

• Ne has a mass # of 20 and an atomic # of 10
• Protons = 10
• Neutrons = 20 - 10= 10
What about the electrons?
• electrons are equal to protons
• So e- = p+ = atomic #
• Ex: He has mass # of 4 and atomic # of 2
• p+ = 2
• no = 2
• e- = 2

Basic Atomic Structure 1:57
Determine the number of subatomic
particles in the following:
• Chlorine has a mass # of 35 and an
atomic # of 17
• p+ = 17, no = 18,   e- = 17

• Potassium has a mass # of 39 and an
atomic # of 19
• P+ = 19,       no = 20        e- = 19
Candy Atoms
• Atom #1 - mass # of 5 and an atomic # of 3.

• Atom #2 – 5 protons and 7 neutrons.

• Atom #3 – Atomic # of 7 and 8 neutrons.
Candy Atoms
• Atom #4 – mass # 18 and 9 electrons

• Atom #5 – build your own candy atom using the candies
that you have. You should be able to accurately
determine:
• Atomic #
• Mass #
• # of protons, neutrons, and electrons
4.3 Modern Atomic
Theory
Bohr Model of the Atom
• Agreed with Rutherford
• Small nucleus w/ lots of
space

• Devised planetary model
• trying to show why e-
were not sucked into p+ in
nucleus of atom.
• e- in specific energy levels
Misconceptions from the Bohr Model
• Bohr model good for diagramming atoms
and energy levels
• e-   do NOT move like planets in
predictable orbits
• Mathematics determine probable
location of e-
Energy Levels
• Possible energies e- can have
• Like floors in hotel
• Floor nearest nucleus - ground floor
The Electron Hotel
• Levels nearer nucleus have lower energy
(ground floor of hotel)

• Electrons fill energy levels from inside -
outside. (ground floor - top floor of
Electron Hotel)
Electron distribution in an Atom   Energy
Level
3d        3
3p
3s
ENERGY

2p                 2
2s

1
1s
NUCLEUS
Energy Levels
• Can’t stand “in between”
steps in hotel stairwell
• e-’s can’t exist “in
between” energy levels
• Must absorb energy to
move up energy levels
• Must lose to move down
Evidence of Energy Levels
• Energy gains & loses can be measured
• As e- drop orbitals, energy released in
form of light/heat
• Like in fireworks (2:34)
Electron Cloud Model
• Electrons travel around
nucleus in random orbits.
• cannot predict location at any
given moment.
• fast, appear to form “cloud”
around nucleus.
• Ex. - Airplane propeller
Atomic Orbitals
• Rooms in “Electron Hotel”
• Region of space where e- likely located
• Each orbital can have 2 e- max
• Denser region = higher probability

Energy Levels, Orbitals, and Electrons

Energy        Number of     Maximum number of
Level        Orbitals          electrons
(floors in   (hotel rooms)      (occupants)
hotel)
1             1                   2

2             4                   8

3             9                   18

4             16                  32
Electron Configuration
• Arrangement of e-’s (occupants) in orbitals
(rooms)
• Each orbitals holds 2 e-’s max (1 double
bed)
• Stable when e-’s in orbitals w/ least energy
• Ground state
• i.e. Lithium (atomic # = 3) has 1st 2 e-’s in the
1st energy level (fills up 1 room w/ double bed)
• 3rd e- goes to 2nd energy level
Electron Configuration
• If Lithium absorbs
enough energy, 3rd e-
jumps energy levels
• Excited state
• Less stable (like gymnast
on beam)
• Eventually releases
energy (often as light)
• Returns to ground state
How exactly are the particles
arranged?
• Bohr Model of the atom:
Electrons move in orbits at fixed distances from the nucleus (planetary
model)
All of the
protons and
the neutrons
The 3rd ring
can hold up
to 18 e-                                           The 1st ring can
The 4th ring                                    hold up to 2 e-
and any after                               The 2nd ring can
can hold up to                              hold up to 8 e-
32 e-
What does carbon look like?
Mass # = 12            atomic # = 6

6 p and 6 n live
in the nucleus

p+ = 6        no = 6         e- = 6
Drawing Atoms
• Draw the following atoms in your notes:
• 1. Beryllium has an atomic # of 4 and a mass # of 9
Beryllium Atom
Drawing Atoms
• 2. Sodium has an atomic # of 11 and a mass # of 23
Sodium Atom

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