Download Atomic Structure

Unit II—Part 3



Atom: the smallest unit of matter that
retains the identity of the substance
First proposed by
Democritus around
420 B.C.
“Atomos” in Greek
means indivisible

Atoms are composed of 2 regions:


Nucleus: the center of the atom that contains
the mass of the atom
Electron cloud: region that surrounds the nucleus
that contains most of the space in the atom
Electron
Cloud
Nucleus

The nucleus contains 2 of the 3 Subatomic
Particles:
Protons: positively (+) charged subatomic
particles
 Neutrons: neutrally ( ) charged subatomic
particles


The 3rd Subatomic Particle resides
outside of the nucleus in the electron
cloud
 Electron: the subatomic particle
with a negative charge and relatively
no mass


Protons and neutrons live compacted in
the tiny positively charged nucleus
accounting for more than 99% of the
mass of the atom
The negatively charged electrons are
small and have a relatively small mass
but occupy a large volume of space
outside the nucleus

In an atom:

The # of protons = the # of electrons
 If 20 protons are present in an atom then 20
electrons are there to balance the overall
charge of the atom—atoms are neutral

The neutrons have no charge; therefore
they do not have to equal the number of
protons or electrons

Atomic number: this number indicates the
number of protons in an atom
 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 = He, 29 protons = Cu
Atomic Math Challenge
8
Atomic Number
O
Element Symbol
Oxygen
Element Name
15.99
Atomic Mass
http://www.videopediaworld.com/vid
eo/16322/Chemistry-of-Life-Atomsand-Elements

Mass number: the number of protons and
neutrons in the nucleus


Ex: Hydrogen can have a mass of 3.
Since it has 1 proton it must have 2 neutrons
# of neutrons = mass # - atomic #

Li has a mass number of 7 and an atomic
number of 3



Protons = 3 (same as atomic #)
Neutrons= 7-3 = 4 (mass # - atomic #)
Ne has a mass number of 20 and an
atomic number of 10
Protons = 10
 Neutrons = 20 - 10= 10


The electrons are equal to the number of
protons


So e- = p+ = atomic #
Ex: He has a mass # of 4 and an atomic
# of 2
= 2
 no = 2
 e- = 2
 p+

Cl has a mass # of 35 and an atomic
# of 17


p+ = 17,
no = 18,
e- = 17
K has a mass # of 39 and an atomic
# of 19

P+ = 19,
no = 20
e- = 19
H:\Chemistry
Websites\lsps07_int_theatom\
Shortcut to
lsps07_int_theatom.lnk
Pass out the student
worksheet from “The
Atoms Family” Lesson
Atomic Math Challenge
at this time and complete in
class

Bohr Model of the atom:
Reviewers think this could lead to misconceptions!
The 3rd
energy ring
can hold up to
18 e-
The 4th energy
ring and any
after can hold
up to 32 e-
All of the
protons p+ and
neutrons n are
within the
nucleus
The 1st energy
ring can hold up
to 2 eThe 2nd energy
ring can hold
up to 8 e-
Mass # = 12
atomic # = 6
6 p and 6 n live
in the nucleus
p+ = 6
no = 6
e- = 6
Bohr Model Practice
Lithium
Atomic #
3
Atomic Mass 7
P+ = 3
Protons
3
Neutrons
4
N =4
Electrons
3
# Electrons
1st energy ring / level
2
2d energy ring / level
1
3d energy ring / level
4th energy ring / level
Bohr Model Practice
Aluminum
Atomic # 13
Atomic Mass 27
Protons
P+ = 13
N = 14
13
Neutrons
14
Electrons
13
# Electrons
1st energy ring / level
2
2d energy ring / level
8
3d energy ring / level
3
4th energy ring / level
none
Hand out the Bohr
Model Practice
worksheet and assign 8
different atoms for
students to complete
their models