Atomic Structure
Unit 3
History of the Atom
 Watch Discovery Education Video –Discovering the Elements
section 1-8
 Complete the questions on page 4 about the Scientists who
helped with the development of the Atomic theory.
Atomic Structure
-
Protons
+
N
Electronsoutside the
nucleus
NUCLEUS
+
N
-
Neutrons
Outside the nucleus
Complete the following table:
Subatomic Location
Particle
Electron
Proton
Neutron
Charge
Mass
Complete the following table:
Subatomic
Particle
Electron
Location
Charge
(-)
Mass
Proton
Electron
Cloud
Nucleus
(+)
0 amu
(teeny tiny!)
1 amu
Neutron
Nucleus
Neutral
1 amu
Reading the Periodic Table
* Atomic #: The number of _protons_ in an atom. It
equals the number of _electrons_ in a neutral atom.
* Mass number = __protons__ + neutrons
* # of neutrons = _Mass_#___ - ___atomic number_____
* Atomic Mass: The _average__of all naturally occurring
isotopes.
Observe the models of atoms at your Lab stations.
Use the results and your periodic table to
complete the chart and the following questions.
Homework: Complete page 6
NOTES: Isotopes and Ions
Warm-up:
Isotopes:
 Isotopes - is a version of an atom with the same
number of PROTONS, but different number of
NEUTRONS.
-If an atom is an isotope you name it using the element
name followed by the mass number.
* Ex: carbon – 12 and carbon -14
-Writing Isotope Symbols:
1.
2.
3.
Write the atomic symbol for the element
To the top left of the symbol write the mass # of the isotope.
Beneath that (to the bottom left of the symbol). Write the atomic number of the element.
Ex: Label the following
Carbon-14 is written like this:
Mass #
14
6
Atomic #
Element
Symbol
Isotope Examples:
14
12
6
and
6
How many protons does How many protons does
Carbon-14 contain?
6
How many neutrons does
Carbon-14 contain?
14-6 = 8
Carbon-12 contain?
6
How many neutrons does
Carbon-12 contain?
12-6= 6
* Atoms as a rule are all neutral in
charge, meaning that the number of
protons and electrons in the atoms are
equal.
Ions:
Ions are charged atoms (+ or -)
Formed when an atom GAINS or
LOSES electrons
Ions
 Cations
 Positively (+) charged atoms
 Form by LOSING electrons
 Usually formed by metals
Examples Lithium - 7
+ Protons: 3
Neutrons: 4
Charge: 1+
Electrons: 2
Ions
 Anions
 Negatively (-) charged atoms
 Form by GAINING electrons
 Usually formed by nonmetals
 Examples
2-
Sulfur - 32
Protons: 16
Neutrons: 16
Charge: 2Electrons: 18
Page 9 -10
 Complete the table as directed on Pg. 9.
 Complete the chart and answer the
questions on Pg. 9 in group of 2 (no
larger!).
 Homework: Pg. 10
1
Neutral
0
2
Neutral
0
3
Neutral
0
4
Neutral
0
5
Neutral
0
6
7
8
9
10
11
12
Charge
Neutral/Isotop
e/Ion
Mass Number
Atomic
Number
#Electrons
#Neutrons
#Protons
Atom name
with mass #
Isotope Symbol
Atom#
Isotopes and Average Atomic Mass
* Compare & contrast Mass Number and Atomic Mass:
Atomic Mass Calculations
 Atomic mass is the weighted average of the
masses of all naturally occurring isotopes.
 Atomic Mass=
Σ[(Percent Abundance) x (Mass of Isotope)]
Σ = take the sum of; add them all up at the end!
 Sample Calculations together.. 
Atomic StructureInside the Nucleus
 Protons
 Positively (+) charged particles
 Equal to the atomic number
 Identity of atoms is based on # of protons in
Nucleus
 Contribute to the mass of the atom
 Proton mass = 1amu
 amu= atomic mass unit
Atomic StructureInside the Nucleus
 Neutrons
 Neutral particles (no charge)
 Help hold nucleus together; contribute to
stability
 Neutrons + Protons= mass number
 Neutron mass = 1amu
Atomic Structure-
Outside the Nucleus (Electron Cloud)
 Electrons
 Negatively (-) charged particles
 Responsible for the CHEMICAL PROPERTIES of
the atom
 In a neutral atom (no charge), protons=electrons
 Very little mass
 ~0 amu
Reading the Periodic Table Elements
Atomic
= # Protons
6
(element identity!)
number
Element
Symbol
Atomic
Mass
12.01
Carbon
= weighted average
of isotope atomic
masses
Complete the following table:
Complete Mass
Symbol
Number
70
34
Se
Atomic
Number
Protons
Neutrons
Electrons
16
14
Complete Mass
Symbol
Number
30
14
70
34
Si
14+16
= 30
Se 70
Atomic
Number
Protons
Neutrons
Electrons
14
14
16
14
34
70-34
= 36
34
34
+=
= Cations