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Fundamental Laws of Chemistry
and Atomic Theory
CP Chemistry Unit 2
Names and Symbols for the
Elements
Each element has a name and a symbol.
 The symbol usually consists of the first one or two
letters of the element’s name.
• Examples:
Oxygen
Krypton
O
Kr
 Sometimes the symbol is taken from the element’s
original Latin or Greek name.
• Examples:
gold Au
lead Pb
aurum
plumbum
Antoine Lavoisier
1743-1794
Discovered oxygen and hydrogen
Helped create the metric system
Helped put together one of the
first lists of the elements
Law of Conservation of Mass
Showed that several reactions were
occurring because of interactions
with oxygen.
Highly quantitative chemical reactions
lead him to the Law of Conservation
of Mass
The mass of the reactants must equal the
mass of the products
Law of Conservation of Mass:
The total mass of substances does not
change during a chemical reaction.
reactant 1
+
reactant 2
product
=
total mass
Quick Video:
https://www.youtube.com/watch?v=Wwmsy4huZQ0
total mass
Joseph Proust (France 1799)
Law of Definite
Proportions:
A given compound
always contains elements
in a certain proportion by
mass. (Constant
composition).
Atoms combine in whole number ratios, so
their proportion by mass will always be the
same.
Example: H2O is always made up of 2
atoms of H and one atom of O.
The ratio of O to H in water is always 16:2 or
8:1.
Example:
KCl always contains one atom of K for
every one atom of Cl
In KCl, potassium and chlorine always
have a ratio of “39.09 to 35.45” or “1.1 to
1” by mass.
Law of Multiple Proportions (John Dalton)
When the same two elements combine to
form more than one compound:
the ratios of the mass of one element in
the first compound to its mass in the
second compound, (as it combines with
the same mass of the other element), can
always be expressed as ratios of small
whole numbers( ex: 1:3 or 2:5).
Dalton’s Atomic Theory (1800)
•
Dalton’s Atomic theory states:
 All elements are composed of atoms.
 All atoms of a given element are identical.
* Isotopes!
 Atoms of different elements are different.
 Compounds consist of the atoms of different
elements.
 Atoms are not created or destroyed in a
chemical reaction.
* Fission! Fusion! Synthetic Elements
J. J. Thomson
Thomson knew that the atom was neutral
overall.
If electrons existed, there must also be
something positive
Thomson proposed model became known
as the Plum-Pudding Model
J. J. Thomson
Plum-Pudding Model
Lord Ernest Rutherford
 1871-1937
 Father of Nuclear
Physics
 Proved that
radioactivity
involved the
transmutation of
one element into
another
 Received the Nobel
Prize in Chemistry
in 1908
http://en.wikipedia.org/wiki/Ernest_Rutherford
Gold Foil Experiment
A beam of alpha particles (2p+, 2n) were
directed at a thin gold foil
The Plum-Pudding Model
Atoms had very low density.
Almost all the particles should pass through
the atoms in the gold foil
Gold Foil Experiment
Actual Observations:
• Some particles went
straight through the
gold foil
• Some were deflected
• Some bounced back
at a high angle
Bohr Model
The lowest state
is the ground
state
Electrons with
additional energy
can occupy an
excited state
Introduction to the Modern Concept
of Atomic Structure
Comparing the Parts of an Atom
Isotopes
Isotopes are atoms with the same number
of protons but different numbers of
neutrons.
The Periodic Table
Alkali
 Nonmetals, Metals, Metalloids, Noble
gases
Alkaline
(earth)
Halogen Noble Gas
The Periodic Table

Periods: Are arranged horizontally
across the periodic table (rows 1-7)

These elements have the same number of valence
shells.
1
IA
1
2
IIA
13
IIIA
2nd Period
2
3
3
IIIB
4
IVB
5
VB
4
6th Period
5
6
7
6
VIB
7
VIIB
8
9
VIIIB
10
11
IB
12
IIB
14
IVA
15
VA
16
VIA
17
VIIA
18
VIIIA
Natural States of the Elements
Diatomic Molecules
Natural States of the Elements
Diatomic Molecules
Formulas of Compounds
A compound is represented by a chemical
formula in which the number and kind of
atoms present is shown by using the
element symbols and subscripts.
Example: the simple sugar, glucose
Formulas of Compounds
Molecules and Ions
Chemical Bonds: forces that hold atoms together
Covalent Bonding: bonds between atoms formed by the
sharing of electrons.
Ionic Bonding: bonds between atoms formed by the
attractions among opposite charged ions.
Cation – an atom that has lost electrons forming a positive ion.
Ex: Na → Na+ + eAnion – an atom that has gained electrons forming a negative
ion.
Ex: Cl + e- → Cl-