Transcript Chapter 3_Lecture

Chapter 3 Matter and Energy
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Matter
• Matter is any substance that has mass and
occupies volume.
• Matter exists in one of three physical states:
– Solid (s)
– Liquid (l)
– Gas (g)
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Gaseous State
• In a gas, the particles of matter are far apart and
uniformly distributed throughout the container.
• Gases have an indefinite shape and assume the
shape of their container.
• Gases can be compressed and have an indefinite
volume. They can be compressed into a liquid, like
liquid Nitrogen, N2(l) or a solid, like dry ice,
CO2(s).
• Gases have the most energy of the three states of
matter.
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Liquid State
• In a liquid, the particles of matter are loosely
packed and are free to move past one another.
• Liquids have an indefinite shape and assume the
shape of their container.
• Liquids cannot be compressed and have a definite
volume.
• Liquids have less energy than gases but more
energy than solids.
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Solid State
• In a solid, the particles of matter are tightly packed
together.
• Solids have a definite, fixed shape.
• Solids cannot be compressed and have a definite
volume.
• Solids have the least energy of the three states of
matter.
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Physical States of Matter
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Changes in Physical State
• Most substances can exist as either a solid, liquid,
or gas.
• Water exists as a solid below 0 °C; as a liquid
between 0 °C and 100 °C; and as a gas above
100 °C.
• A substance can change physical states as the
temperature changes.
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Solid ↔ Liquid Phase Changes
• When a solid changes to a liquid, the phase change
is called melting.
• A substance melts as the temperature increases.
• When a liquid changes to a solid, the phase change
is called freezing.
• A substance freezes as the temperature decreases.
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Liquid ↔ Gas Phase Changes
• When a liquid changes to a gas, the phase change
is called vaporization.
• A substance vaporizes as the temperature increases.
• When a gas changes to a
the phase change is
condensation.
liquid,
called
• A substance condenses as
the temperature decreases.
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Solid ↔ Gas Phase Changes
• When a solid changes directly to a gas, the phase
change is called sublimation. Example: Moth ball.
• A substance sublimes as the temperature increases.
• When a gas changes directly to a
the phase change is
called
deposition.
solid,
• A substance undergoes
deposition as the
temperature decreases.
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Summary of State Changes
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Classifications of Matter
• Matter can be divided into two classes:
– Mixtures (also called solutions)
– pure substances
• Mixtures are composed of more than one
substance and can be physically separated into its
component substances.
• Pure substances are composed of only one
substance and cannot be physically separated.
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Mixtures
• There are two types of mixtures:
– homogeneous mixtures
– heterogeneous mixtures
• Homogeneous mixtures have uniform properties throughout.
– Beer; salt and water.
– Air.
– Alloy.
• Heterogeneous mixtures do not have uniform properties throughout.
– Sand and water.
– Sulfur and sand.
– Oil and water.
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Pure Substances
• There are two types of pure substances:
– compounds
– elements
• Compounds can be chemically separated into
individual elements.
– Water is a compound that can be separated into
hydrogen and oxygen.
• An element cannot be broken down further by
chemical reactions.
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Matter Summary
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Occurrence of the Elements
• There are over 100 elements that occur in nature;
81 of those elements are stable.
• Only 10 elements account for 95% of the mass of
the Earth’s crust:
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Elements In the Human Body
• Oxygen is the most common element in both the
Earth’s crust and in the human body.
• While silicon is the second most abundant element
in the crust, carbon is the second most abundant in
the body.
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Names of the Elements
• Each element has a unique name.
• Names have several origins:
– hydrogen is derived from Greek
– carbon is derived from Latin
– scandium is named for Scandinavia
– nobelium is named for Alfred Nobel
– yttrium is named for the town of Ytterby, Sweden
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Element Symbols
• Each element is abbreviated using a chemical
symbol.
• The symbols are 1 or 2 letters long.
• Most of the time, the symbol is derived from the
name of the element.
– C is the symbol for carbon
– Cd is the symbol for cadmium
• When a symbol has two letters, the first is
capitalized and the second is lowercase.
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Other Element Symbols
• For some elements, the chemical symbol is
derived from the original Latin name.
Gold – Au
Sodium – Na
Silver – Ag
Antimony – Sb
Copper – Cu
Tin – Sn
Mercury – Hg
Iron – Fe
Potassium – K
Tungsten – W
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Types of Elements
• Elements can be divided into three classes:
– Metals: Na, Mg, Al, Cr, Hg,…. etc.
Note: All metals are soild except Hg which is a liquid.
– Nonmetals: H, C, P, Cl, Ar,….etc.
– All nonmetals are either solid or gas except Br2 which is a liquid.
– semimetals or metalloids: B, Si, Ge,….etc.
• Semimetals have properties midway between those of
metals and nonmetals.
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Metal Properties
• Metals are typically solids with high melting
points and high densities and have a bright,
metallic luster.
• Metals are good conductors of heat and electricity.
• Metals can be hammered into thin sheets and are
said to be malleable.
• Metals can be drawn into fine wires and are said to
be ductile.
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Nonmetal Properties
• Nonmetals typically have low melting points and low
densities and have a dull appearance.
• Nonmetals are poor conductors of heat and electricity.
• Nonmetals are not malleable or ductile and crush into a
powder when hammered.
• 11 nonmetals occur naturally in the gaseous state.
They are H2, N2, O2, F2, Cl2, He, Ne, Ar, Kr, Xe, Rn.
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Summary of Properties
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Periodic Table of the Elements
• Each element is assigned a number to identify it.
It is called the atomic number. It’s also called the
proton number.
• Hydrogen is 1; helium is 2; up to uranium, which
is 92.
• The elements are arranged by atomic number on
the periodic table.
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The Periodic Table
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Metals, Nonmetals, & Semimetals
• Metals are on the left side of the periodic table,
nonmetals are on the right side, and the semimetals
are in between.
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Physical States of the Elements
• Shown are the physical states of the elements at
25 °C on the periodic table.
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Law of Definite Composition
• The law of definite composition states that
“Compounds always contain the same elements in
a constant proportion by mass.”
• Water is always 11.19% hydrogen and 88.81%
oxygen by mass, no matter what its source.
• Ethanol is always 13.13% hydrogen, 52.14%
carbon, and 34.73% oxygen by mass.
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Chemical Formulas
• A particle composed of two or more nonmetal
atoms is a molecule.
• A chemical formula
expresses the number and
types of atoms in a molecule.
• The chemical formula of
sulfuric acid is H2SO4.
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Writing Chemical Formulas
• The number of each type of atom in a molecule is
indicated with a subscript in a chemical formula.
• If there is only one atom of a certain type, no ‘1’ is
used.
• A molecule of the vitamin niacin has 6 carbon
atoms, 6 hydrogen atoms, 2 nitrogen atoms, and
1 oxygen atom. What is the chemical formula?
C6H6N2O
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Interpreting Chemical Formulas
• Some chemical formulas use parentheses to clarify
atomic composition.
• Ethylene glycol, a component of some antifreezes,
has a chemical formula of C2H4(OH)2. There are 2
carbon atoms, 4 hydrogen atoms, and 2 OH units,
giving a total of 6 hydrogen atoms and 2 oxygen
atoms. How many total atoms are in ethylene
glycol?
• Ethylene glycol has a total of 10 atoms.
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Physical & Chemical Properties
• A physical property is a characteristic of a pure
substance that we can observe without changing
its composition.
• Physical properties include appearance, melting
and boiling points, density, conductivity, and
physical state.
• A chemical property describes the chemical
reactions of a pure substance.
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Physical & Chemical Change
• A physical change is a change where the chemical composition of the substance
is not changed.
These include changes in physical state or shape of a pure substance.
Simply put, you’ll always be able to get it back when a substance undergoes
physical changes by adjusting temperature, pressure, etc.
Example: Sublimation, melting, boiling, etc.
• A chemical change is a chemical reaction.
The composition of the substances changes during a chemical change.
Simply put, you cannot get it back when a substance undergoes a chemical
reaction.
Example: Boiling an egg, fruits ripe, nail rust, combustion (or burning or
explosion), decomposition, combination, oxidation-reduction, baking a potato,
color of carpet faded by sunlight, magnesium metal dissolves in vinegar to
produce hydrogen gas, etc. In nutrition, it’s metabolism or digestion.
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Evidence for Chemical Changes
• gas release (bubbles)
• light or release of heat energy
• formation of a precipitate
• a permanent color change
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Conservation of Mass
• The mass of substances before a chemical change
was always equal to the mass of substances after a
chemical change.
• This is the law of conservation of mass.
• Matter is neither created nor destroyed in physical
or chemical processes.
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Conservation of Mass Example
• If 1.0 gram of hydrogen combines with 8.0 grams
of oxygen, 9.0 grams of water is produced.
• Consequently, 3.0 grams of hydrogen combine
with 24.0 grams of oxygen to produce 27.0 grams
of water.
• If 50.0 grams of water decompose to produce 45.0
grams of oxygen, how many grams of hydrogen
are produced?
50.0 g water – 45.0 g oxygen = 5.0 g hydrogen
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Potential & Kinetic Energy
• Potential energy, PE, is stored energy; it results
from position or composition.
• Kinetic energy, KE, is the energy matter has as a
result of motion.
• Energy can be converted between the two types.
• A boulder at the top of the hill has potential energy;
if you push it down the hill, the potential energy is
converted to kinetic energy.
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KE, Temperature, and Physical State
• All substances have kinetic energy no matter what
physical state they are in.
• Solids have the lowest kinetic energy, and gases
have the greatest kinetic energy.
• As you increase the temperature of a substance, its
kinetic energy increases.
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Law of Conservation of Energy
• Just like matter, energy cannot be created or
destroyed, but it can be converted from one form
to another.
• This is the law of conservation of energy.
• There are six forms of energy: heat, light,
electrical, mechanical, chemical, and nuclear.
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Energy and Chemical Changes
• In a chemical change, energy is transformed from
one form to another. For example:
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Law of Conservation of Mass & Energy
• Mass and energy are related by Einstein’s theory
of relativity, E = mc2.
• Mass and energy can be interchanged.
• The law of conservation of
mass and energy states that
the total mass and energy of
the universe is constant.
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Chemistry Connection: Al Recycling
• Although aluminum is very
abundant in the Earth’s crust,
it is difficult to purify it from
its ore.
• The energy from 8 tons of
coal is required to produce 1
ton of aluminum metal from
its ore.
• However, it only takes the
energy from 0.4 tons of coal
to produce 1 ton of aluminum
from recycled scrap.
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Chapter Summary
• Matter exists in three physical states:
– solid
– liquid
– gas
• Substances can be converted between the three
states.
• Substances can be mixtures or pure substances.
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Chapter Summary, continued
• Pure substances can be either compound or
elements.
• The elements are arranged in the periodic table.
• Each element has a name and a 1- or 2-letter
symbol.
• Elements are classified as either metals, nonmetals,
or semimetals.
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Chapter Summary, continued
• A physical change is a change in physical state or
shape.
• A chemical change is a change in the chemical
composition of a substance.
• Both mass and energy are conserved in chemical
and physical changes.
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