what is matter? - doral academy preparatory school · 2017-07-27 · breaking down mixtures and...
TRANSCRIPT
Matter Section 1
What is Matter?
〉How can matter be classified?
〉Every sample of matter is either an element, a
compound, or a mixture.
• matter: anything that has mass and takes up
space
Matter Section 1
Elements
〉Why are carbon and copper classified as elements?
〉Each element is made of one kind of atom.
• element: a substance that cannot be separated or
broken down into simpler substances by chemical means
• atom: the smallest unit of an element that maintains
the properties of that element
Matter Section 1
Elements in the Human Body
Matter Section 1
Elements, continued
• Elements are represented by symbols. • Atoms that make up a molecule act as a unit.
• molecule: a group of atoms that are held together by chemical forces; a molecule is the smallest unit of matter that can exist by itself and retain all of a substance’s chemical properties
Matter Section 1
Compounds
〉How are elements related to compounds?
〉Each molecule of a compound contains two or more elements that are chemically combined. Elements combine chemically to form a compound.
• compound: a substance made up of atoms of two or more different elements joined by chemical bonds
Matter Section 1
Compounds, continued
• Compounds have unique properties.
• Chemical formulas represent compounds.
– The following chemical formula represents the compound
for indigo:
Matter Section 1
Pure Substances and Mixtures
〉What is the difference between a pure substance and a mixture?
〉Elements and compounds are pure substances, but mixtures are not.
• pure substance: a sample of matter, either a single
element or a single compound, that has definite chemical and physical properties
• mixture: a combination of two or more substances
that are not chemically combined
Matter Section 1
Pure Substances and Mixtures,
continued • Mixtures are classified by how thoroughly the
substances mix. – heterogeneous mixture: substances aren’t mixed uniformly
and are not evenly distributed
– homogeneous mixture: substances are evenly distributed, and the mixture is the same throughout
– miscible: substances that can be mixed
– immiscible: substances that cannot be mixed
• Gases can mix with liquids.
Matter Section 1
Types of Mixtures
10.1 The Nature of Matter
Matter is a term used to describe anything
that has mass and takes up space.
Greek philosophers Democritus and
Leucippus proposed that matter is made
of tiny particles called atoms.
Atoms were an idea that few believed.
The first evidence was called Brownian
motion for Robert Brown, who first noticed
the jerky motion of tiny particles.
10.1 Elements
An element is a pure
substance that cannot be
broken down into other
substance by chemical or
physical means.
All of the matter you are
ever likely to experience
is made from one or more
elements in nature.
10.1 Elements
For example, water
can be broken down
into its elements,
hydrogen and oxygen,
when energy is added.
10.1 Atoms
A single atom is the smallest particle
that retains the chemical identity of
the element.
10.1 Compounds and elements
Compounds are two or more
different elements chemically
bonded together.
10.1 Examples of compounds
Compounds
contain more
than one type
of atom joined
together.
10.1 Molecules
A molecule is a group of two or
more atoms joined together
chemically.
10.1 Mixtures
Many substances
you encounter are
a mixture of
different elements
and compounds.
How many atoms are
in this mixture? How many molecules
are in this mixture?
10.1 Elements, compounds, and mixtures
Can you distinguish between atoms and
molecules in these images?
Matter Section 2
Physical Properties
〉Why are color, volume, and density classified as
physical properties?
〉Physical properties are characteristics that can
be observed without changing the identity of the
substance.
Matter Section 2
Physical Properties, continued • Physical properties can help identify substances. • Physical properties can be observed or measured.
– Examples: shape, color, odor, texture, state, melting point,
boiling point, strength, hardness, magnetism, the ability to conduct electricity or heat
– melting point: the temperature and pressure at which a
solid becomes a liquid – boiling point: the temperature and pressure at which a
liquid becomes a gas
• Physical properties help determine uses.
Matter Section 2
Physical Properties, continued
• Density is a physical property.
– density: the ratio of the mass of a substance to the volume of the substance
– common unit of density is g/cm3
• Density is different from weight.
massdensity ,
voor
lu
me
mD
V
Matter Section 2
Math Skills
Density
If 10.0 cm3 of ice has a mass of 9.17 g, what is
the density of ice?
1. List the given and unknown values.
Given: mass, m = 9.17 g
volume, V = 10.0 cm3
Unknown: density, D = ? g/cm3
Matter Section 2
Math Skills, continued
2. Write the equation for density.
density = mass/volume, or D = m/V
3. Insert the known values into the equation, and
solve.
D = 0.917 g/cm3
mD
V
3
9.17 g
10.0 cmD
Matter Section 2
Chemical Properties
〉Why are flammability and reactivity classified
as chemical properties?
〉A chemical property describes how a
substance changes into a new substance,
either by combining with other elements or by
breaking apart into new substances.
Matter Section 2
Chemical Properties, continued
• Flammability is a chemical property.
– flammability: the ability to burn
• Reactivity is a chemical property.
– reactivity: the capacity of a substance to combine
chemically with another substance
Matter Section 2
Chemical Properties, continued
• Physical and chemical properties are different.
– Physical properties can be observed without changing the identity of a substance.
– Chemical properties can be observed only in
situations in which the identity of the substance changes.
12.1 Properties of Solids
Different kinds of matter have
different characteristics.
Characteristics that can you
observe directly are called
physical properties.
Physical properties include
color, texture, density,
brittleness, and state (solid,
liquid, or gas). Ex. Iron is solid at
room temp.
12.1 Properties of Solids
A physical change is any change in
the size, shape, or phase of matter
in which the identity of a
substance does not change.
For example, when water is frozen,
it changes from a liquid to a solid.
12.1 Properties of Solids
Properties that can only be
observed when one
substance changes into a
different substance are
called chemical properties.
Any change that transforms
one substance into a
different substance is called
a chemical change. Ex. If you leave a nail
outside, it rusts.
12.1 Properties of Solids
The density of a solid
material depends on
two things:
1. the individual mass of
each atom or molecule,
2. how closely the atoms
or molecules are
packed together. Carbon atoms in
diamond are packed
very tightly.
12.1 Properties of Solids
Paraffin wax is also
mostly carbon, but its
density is only 0.87
g/cm3.
Paraffin’s carbon
atoms are mixed with
hydrogen atoms in
long molecules that
take up more space.
The density of paraffin is low
compared to diamond.
12.1 Properties of Solids
The atoms or molecules in a solid are
arranged in two ways.
1. If the particles are arranged in an
orderly, repeating pattern, the
solid is crystalline.
2. If the particles are arranged in a
random way, the solid is
amorphous.
12.1 Properties of Solids Metals don’t look
like “crystals”
because solid
metal is made
from very tiny
crystals fused
together in a
jumble of
different
orientations.
12.1 Mechanical properties
“Strength” describes the ability of a
solid object to maintain its shape even
when force is applied.
12.1 Mechanical properties
Tensile strength is a measure of how
much stress a material can withstand
before breaking.
12.1 Mechanical properties
Hardness measures a solid’s
resistance to scratching.
How might you compare the hardness of these two metals?
12.1 Mechanical properties
Elasticity describes a
solid’s ability to be
stretched and then return
to its original size.
Brittleness is defined as
the tendency of a solid to
crack or break before
stretching very much.
12.1 Mechanical properties
A ductile material can
be bent a relatively large
amount without
breaking.
The ductility of many
metals, like copper,
allow then to be drawn
into wire.
12.1 Mechanical properties
Malleability measures a
solid’s ability to be
pounded into thin
sheets.
Aluminum is a highly
malleable metal.
Matter Section 3
Physical Changes
〉Why is getting a haircut an example of a physical
change?
〉A physical change affects one or more properties of
a substance without changing the identity of the
substance.
• physical change: a change of matter from one form to
another without a change in chemical properties
Matter Section 3
Physical Changes, continued
• Physical changes do not change
a substance’s identity.
– Examples of physical
changes: cutting, crushing,
reshaping, changing state
• Dissolving is a physical
change.
Matter Section 3
Chemical Changes
〉Why is baking bread an example of a chemical change?
〉A chemical change happens when one or more substances are changed into entirely new substances that have different properties.
• chemical change: a change that occurs when one or more
substances change into entirely new substances with different properties
Matter Section 3
Chemical Changes
Matter Section 3
Chemical Changes, continued
• Chemical changes happen everywhere.
– Examples of chemical changes: burning, rusting, digesting, decomposing
• Chemical changes form new substances.
• Chemical changes can be detected.
– Signs include: change of color, change of smell, fizzing, production of heat, production of sound, production of light
• Chemical changes cannot be reversed by physical changes.
Matter Section 3
Breaking Down Mixtures and
Compounds
〉How can mixtures and compounds be broken down?
〉Mixtures can be separated by physical changes, but
compounds must be broken down by chemical
changes.
Matter Section 3
Breaking Down Mixtures and
Compounds, continued • Mixtures can be physically separated.
• Examples of separating a mixture:
– Separating saltwater into its parts by heating it: When the water
evaporates, the salt remains.
– Using a distillation device to heat a mixture whose components have different boiling points: The component that boils and evaporates first separates from the mixture.
– Using a centrifuge: The mixture spins rapidly until the components separate.
Matter Section 3
Breaking Down Mixtures and
Compounds, continued • Some compounds can be broken down through chemical
changes.
• Examples of separating a compound:
– When mercury(II) oxide is heated, it breaks down into the
elements mercury and oxygen.
– When a current is passed through melted table salt, the elements sodium and chlorine are produced.
– When you open a bottle of soda, carbonic acid in the soda breaks down into carbon dioxide and water.
10.3 Phases of Matter
On Earth, pure
substances are
usually found as
solids, liquids, or
gases.
These are called
phases of matter.
10.3 The phases of matter
A solid holds its
shape and does not
flow.
The molecules in a
solid vibrate in place,
but on average, don’t
move far from their
places.
10.3 The phases of matter
A liquid holds its
volume, but does
not hold its
shape—it flows.
Liquids flow
because the
molecules can
move around.
10.3 The phases of matter
A gas flows like a liquid,
but can also expand or
contract to fill a
container.
A gas does not hold its
volume.
The molecules in a gas
have enough energy to
completely break away
from each other.
10.3 The phases of matter
When they are close together,
molecules are attracted through
intermolecular forces.
10.3 The phases of matter
The forces in chemical bonds are
stronger than intermolecular
forces.
10.3 Intermolecular forces
Within all matter, there is a constant
competition between temperature and
intermolecular forces.
When temperature wins the
competition, molecules fly apart and
you have a gas.
When intermolecular forces win the
competition, molecules clump tightly
together and you have a solid.
10.3 Melting and boiling
The melting point is the
temperature at which a substance
changes from a solid to a liquid.
10.3 Melting and boiling
The temperature at which a liquid
becomes a gas is called the boiling
point.
Notice temperature is constant while ice melts!
10.3 Melting and boiling points of common substances
Materials have a
wide range of
melting and
boiling points.
10.3 Sublimation
Sometimes a solid
can change directly
to a gas when heat
energy is added.
This process is
called sublimation.