Chemistry I
Atomic Structure Chapter 3
I Models
A. Greek’s – indivisible particle of matter. From this we get atom – the smallest part of a substance which
cannot be divided
B. Dalton’s - uniform solid spheres (like billiard balls)
C. Thompson – atom is made up of smaller particles, discovered electrons
D. Rutherford – through the gold foil experiment, he discovered the nucleus and determined that electrons
were negatively charged.
E. Bohr – proposed that electrons orbit around the nucleus. This was a BIG deal!!! Today – we call the electron
path an electron cloud
II Atomic Theories
A. Dalton’s Atomic Theory
a. Each element is composed of extremely small particles called atoms that cannot be subdivided.
b. All atoms of a given element are identical
c. Atoms of different elements have different properties and different masses
d. Compounds are formed when atoms of more than one element combine
e. In a given compound, the relative number and kinds of atoms are constant
B. Laws upon which Dalton’s Atomic Theory is Based
a. Law of Definite Proportions – The elemental composition of a pure compound is always the same.
Compounds are substances composed of two or more elements united chemically in definite
proportions by mass.
b. Law of Conservation of Matter and Energy – Matter and energy are interchangeable, and the total
matter and energy in the universe is constant. In ordinary chemical reactions, the total mass of the
reacting materials is equal to the total mass of the products.
c. Law of Multiple Proportions – When two elements form more than one compound, for a fixed mass
of one element, the mass of the second element is related to the first element by small whole
numbers.
III Atomic Structure – Protons, Neutrons, Electrons
Proton
Neutron
Discovered
Experiments
E Goldstein
(1885)
JJ
Thompson
(1902)
Discovery
E.
Rutherford
(1911)
Gold foil experiment
to find location in
nucleus
HGJ
Moseley
(1914)
Chadwick
(1932)
X rays found atomic
number
Atomic
Weight
(g)
1.675 x 10 -24
Atomic
Weight
(amu)
1.007277
Charge
Location
Importance
Equal by math to
+1
Nucleus
Determines physical &
chemical characteristics of
the element
Number of
electrons in a
neutral atom
Determines atomic
number of element; thus
its periodic relationships
and functions
Atomic Mass #
minus # of neutrons
Used cathode to find
charge/mass ratio
Used alpha rays to
bombard Beryllium to
produce particle
wave of neutrons to
find charge/mass
Atomic Number
1.675x10-24
1.008665
0
Nucleus
Responsible for the
greater mass of the ato
Atomic mass #
minus the atomic
number
FW Aston
(1919)
W Crookes
(1879)
Electron
JJ
Thompson
(1897)
R Millikan
(1909)
Developed mass
spectrograph used to
isolate isotopes of a
given element
Produced cathode
ray composed of
negatively charged
particles
9.11x10-28
5.486x10-4
-1
Shells
Energy levels
about
nucleus
Discovered the
charge/mass ratio of
the electrons
Oil drop exp.
Discovered charge of
electron
1st
Nucleus
Determines the number of
nucleotides or isotopes
that make up the element
2nd
Inner shell electrons give
the atom much of its
stability
Number of protons
Outer shell or valence
electrons are responsible
for the chemical activity of
the element
Mass # = # of
neutrons
3rd
Energy Level: lowest
most
Outer energy level contains valence electrons.
Energy:
lowest
more
mostan equal number of protons and electrons!
How does
an atom become
neutral? By having
IV Periodic Table:
A. Periods
There are 7 periods or rows
1st H and He
2nd Li through Ne
3rd Na through Ar
Etc.
B. Groups or Families
I
2
3
4
5
6
7
H
8
He
Li
Be
Na
Mg
B
C
N
O
F
Ne
Atomic Number
V Atomic Mass Formulae
1. Mole – the amount of a substance that contains the same number of units as the number of atoms in exactly 12
g of Carbon – 16. This is Avogadro’s number of 6.022 x 10 23 particles.
2. Mass to number of atoms = given mass in g of element
6.022 x 10 23 atoms
Molar mass in g of element
3. Number of atoms to mole: # atoms
mole
6.022 x 1023 atoms
4. Mass to moles: given mass in g
moles
Molar mass in g
5. Atomic particle determination
a. Neutrons = mass number of nucleotide – atomic number of element
b. Protons = atomic number of element
c. Electrons = atomic number of element
d. Atomic Mass – average mass of isotopes of an element
e. Mass number – the total protons and neutrons in the nucleus of an atom
6. Atomic
Mass of
Nucleotide
Sum
7.
+
=
# of protons x 1.007277
# of neutrons x 1.008665
# of electrons x 5.486 x 10-4
or
or
or
mass in amu / 6.022 x 1023
=
x 1.673 x 10-24
x 1.675 x 10-24
x 9.110 x 10-28
mass in grams
Determination of atomic weight of an element from its component nucleotide:
% of At Wt x At Mass
+
Nuc’tide #1
% of At Wt x At Mass
+
Nuc’tide #2
% of At Wt x At Mass
+ …
Nuc’tide #3
100
8. Determination of % composition of nucleotides making up the atomic weight of an element
Given at. wt.
of element
Given at. mass of
=
.
x +
heavier isotope
Given at. mass of (100 – x)
lighter isotope
100