Transcript Basics Of Chemistry

Basics Of Chemistry
8th Science 2012
Matter Defined
► Matter
– anything that
has volume or mass.
► Everything
you see
and don’t see.
Definitions
► Element-
pure
substance that cannot
be separated into
simpler substances by
physical or chemical
means.
 Represented by a
symbol – Au stands for
what?
Definitions
► Atom
– Smallest
particle into which an
element can be divided
and still be the same
substance, retaining its
properties
Evolution of the Atomic Theory
►
Democritis – 440 BC
►
Greek philosopher who said that if you cut a substance in
half again and again and again eventually you would
have an “uncuttable” piece
said that all atoms made of a single material formed into
different shapes and they join together to make
different materials
►
►
Greek word atomos, which means
“indivisible”
John Dalton - 1803
► Studied
the
atmosphere and other
gases and developed
atomic theory.
► Dalton demonstrated
that elements
combine in specific
proportions to make
different substances
John Dalton’s Atomic Theory
Dalton’s New System of Chemical Philosophy
►
1. All substances are
made of atoms.
►
2. Atoms are small
particles that cannot be
created, divided, or
destroyed.
Dalton’s Atomic Theory, continued
►
3. Atoms of the same element are identical
in size, mass and other properties.
►
4. Atoms of different elements combine to
make chemical compounds.
►
5. In chemical reactions, atoms are
combined, separated, or rearranged.
J.J. Thomson - 1897
► discovered
that there
are small particles
inside the atom, so
the atom can be
divided into smaller
parts
JJ Thomson, continued
► Experimented,
using a
cathode-ray tube to
discover negative
particles he called
corpuscles
negatively
charged particles
found in all atoms
are now called
electrons
► these
Thomson’s Model
► Plum
Pudding
model
► Described
electrons as
scattered all about the
atom
Ernest Rutherford - 1908
Rutherford, continued
► Discovered
a tiny,
extremely dense,
positively charged
region called a
nucleus
► Most of the atom’s
mass was in the
nucleus and electrons
traveled around the
nucleus
Rutherford cont’d
► said
the atom
was mostly
empty space
Niels Bohr – 1913
► said
the electrons
travel around the
nucleus in definite
paths
Erwin Schrödinger and
Werner Heisenberg - 1926
► Said
electrons travel in
clouds, not definite
paths but we still use
the Bohr Model to
represent atoms.
The Atom
Subatomic Particles
Protons
Determine the identity of the matter
► positively charged particles
► found in the nucleus
► Mass =1.67262158 × 10-27 kilograms
0.000000000000000000000000017 kg
► Each proton is 1 amu

AMU stands for Atomic Mass Unit
Subatomic Particles
Neutrons
Neutrons are the glue that holds the protons
together in the nucleus
►
►
►
no charge
found in the nucleus
mass is 1 amu
Subatomic Particles
Electrons
Determine the reactivity
► Negatively charged
► Found around the nucleus within
electron clouds
► Mass is very small, almost zero
Atoms are NEUTRAL
► Atoms
are neutral
because the
number of
protons equals
the number of
electrons.
How To Read a Square
►
8
►
O
►
►
Oxygen
15.9994
► Elements
are identified
by their atomic
number – the number
of protons. Also
equals the number of
electrons.
► Chemical Symbol
► Element Name
► Atomic Mass
PEN Method
► SLIDE,
SLIDE, ROUND
THE BOTTOM
SUBTRACT TOP
►P = 8
►E = 8
►N = 8
►
8
►
O
►
►
Oxygen
15.9994