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Earth Chemistry
Chapter 4
Page 80
Matter
• Anything that has mass
and takes up space
• Atoms are matter
132
Physical Properties
Physical properties describe matter
Some are observed through the
senses:
– Shape, color, odor, texture
Some can be measured
– Melting point, strength, hardness
– ability to conduct
• electricity (conductivity)
• magnetism
• or heat
Density is a physical
property
D= m/v
•Measured
in units of g/cm3
• Density is how much matter something
has for its volume
• Another way to say it is . . .
how heavy something is for its size
136B
• Density is mass divided by volume
135
Example:
If 10cm3 of ice has a mass of 9.17g,
what is the density of ice?
Mass m=9.17g
Volume = 10cm3
Density is m/v
9.17g  10cm3 = 0.917 g/cm3
135
137B
Physical properties
help determine uses
• Why is copper used in electric power
lines?
• Why is Styrofoam used for coffee
cups?
138
Chemical properties
• Determine how
a substance will
react
• Generally not
as easy to
observe as
physical
properties
• The chemical
composition
changes
A chemical property
describes how a substance
changes into a new
substance
Either by:
• Combining with other elements
• Breaking apart into new
substances
139
Chemical properties
include:
• Reactivity
• Flammabilityability to burn
139
Characteristic properties
help to
identify and classify substances
• Characteristic
Properties are the
physical or chemical
characteristics the
substance is known
for
Example:
• Helium is light and
non-flammable so it
is good for blimps
element
• A substance that
cannot be
separated or
broken down
into simpler
substances by
chemical means
• More than 90
elements occur
naturally on Earth
Atoms
are made of
• Protons
• Neutrons
• Electrons
Parts
of an
Atom
• Atoms are made of protons,
neutrons and electrons
Particle
Proton
Charge
+1
Neutron
0
Electron
-1
Mass
1
(1.67*10-27)
1
(1.67*10-27)
0
(9.00*10-31)
Location
In the nucleus
In the nucleus
Moving around
outside the
nucleus
Elements are classified by the
number of protons their
atoms contain, which is their
atomic number.
This box tells us
the atomic number is 1.
1
H
1.00797
• This means it has
one proton (and so 1
electron)
• The bottom number
is the mass number.
• H, hydrogen, has a
mass of 1.00797.
# of protons= # of electrons
(In a neutral atom)
Neutral Atoms
• The charge of
an atom is
usually neutral
• The number of
protons equals
the number of
electrons
• Ex. C (carbon)
atomic number
of 6, so 6
protons and 6
1
H
1.00797
Mass Number
• The mass number equals the number of
protons and the number of neutrons.
• Mass number = protons + neutrons
• The mass number of Carbon is 12.0107
C
12.0107
6
WS Lesson 23—126 points
Hints:
• Spell Correctly
• Symbol is 1 Capital 1 small
or 1 Capital
• Round mass
• Three columns are the same
– Atomic Number *
– Protons *
– Electrons *
• Neutrons=Mass-Protons
Isotope
An atom with a different
number of neutrons is
called an isotope
Hydrogen usually is a
proton and an electron
If it has a neutron it is
considered an isotope
hydrogen
neutrons
deuterium
tritium
0
1 neutron
2 neutrons
Half-lives
• The rate of decay of an isotope
is called the half-life.
A half life is the amount of time it takes
for half of the amount to decay.
It is constant
• Different elements have different halflives
Radium-226=1620 years
Uranium-238 = 4.5 billion years
Average Atomic Mass
• Because the isotopes of an element have
different masses the periodic table uses
average atomic mass
• Amu---atomic mass unit
• Found by calculating the weighted
average of the atomic masses of the
naturally occurring isotopes
Isotopes of Carbon
•
Notice they have the same number of
protons, different numbers of neutrons
Bohr's Planetary Model
• Electrons orbit the
nucleus like
planets orbiting
the sun.
• The orbits called
electron shells or
orbitals
• close to the
nucleus hold fewer
electrons than
those far away.
Valence Electrons and
Periodic Properties
• Elements in the
periodic table are
arranged in
columns based on
similarities in their
chemical
properties
• These columns
are called groups
Valence Electrons
• Valence electrons
are the electrons
in the outermost
energy level
• Every atom has
between one and
eight valence
electrons
154
Electrons dictate the many properties of
a material including chemical reactivity and
physical attributes, like taste, texture,
appearance and color.
Obscertainer Lab