Transcript Chemical Changes

Table of Contents
Chapter 2: Elements of Chemistry
Section 2.1: Matter has Physical and Chemical
Properties & Changes
Section 2.2: Atoms are the Fundamental
Components of Elements
Section 2.3: Atoms can combine to Form
Compounds
Section 2.4: Most materials are Mixtures
Section 2.5: Chemists Classify Matter as Pure or
Impure
Section 2.6: Elements are Organized in the Periodic
Table by their Properties
Physical and Chemical Properties
1
Physical Properties
• A physical property is a characteristic that
you can observe without changing or trying
to change the composition of the substance.
• How something looks, smells, sounds, or
tastes are all examples of physical properties.
Properties are…
• Words that describe matter (adjectives)
• Physical Properties- a property that can be
observed and measured without changing the
material’s composition.
• Examples- color, hardness, m.p., b.p.
• Chemical Properties- a property that can only
be observed by changing the composition of
the material.
• Examples- ability to burn, decompose,
ferment, react with, etc.
Physical and Chemical Properties
1
Using Your Senses
• You can detect many physical properties
with your senses.
• For example, you can see the color and
shape of an object.
• You can also touch it to feel its texture.
• You can smell the odor or taste the flavor of
some matter.
Physical and Chemical Properties
1
State
• To describe a
sample of matter,
you need to
identify its state.
This property,
known as the state
of matter, is
another physical
property that you
can observe.
Click image to view movie.
Physical and Chemical Properties
1
State
• Perhaps you are most familiar with the three
states of water.
• You can
drink or
swim in
liquid
water.
Physical and Chemical Properties
1
State
• You use the solid state of water, which is ice,
when you put ice cubes in a drink.
• Although
you can’t see
it, water in
the gas state
is all around
you in the
air.
States of Matter
Definite Definite
Volume? Shape?
Solid
Liquid
Gas
YES
YES
NO
Result of a
TemperatureIn Will it
crease?
Compress?
YES
Small
Expans.
NO
NO
Small
Expans.
NO
NO
Large
Expans.
YES
4th state: Plasma - formed at high
temperatures; ionized phase of matter
as found in the sun
Three Main Phases – page 41
Copper Phases - Solid
Copper Phases - Liquid
Copper Phases – Vapor (gas)
Physical and Chemical Properties
1
Size-Dependent Properties
• Some physical propertied depend on the size
of the object.
Describing Matter
•
Properties used to describe matter can be
classified as:
1) Extensive – depends on the amount of
matter in the sample
- Mass, volume, calories are examples
2) Intensive – depends on the type of matter,
not the amount present
- Hardness, Density, Boiling Point
Physical and Chemical Properties
1
Size-Dependent Properties
• Another physical
property that depends
on size is mass, which
is a measurement of
how much matter it
contains.
• Weight is a
measurement of force.
Physical and Chemical Properties
1
Size-Dependent Properties
• Weight depends on the
mass of the object and
on gravity.
• If you were to travel
to other planets,
your weight would
change but your size
and mass would not.
Physical and Chemical Properties
1
Size-Independent Properties
• Another physical property, density, does not
depend on the size of an object.
• Density measures the amount of mass in a
given volume.
• To calculate the density of an object, divide
its mass by its volume.
Physical and Chemical Properties
1
Size-Independent Properties
• Another property,
solubility, also does
not depend on size.
• Solubility is the number
of grams of one substance
that will dissolve in 100 g
of another substance at a
given temperature.
Physical and Chemical Properties
1
Melting and Boiling Point
• The temperature at
which a solid
changed into a
liquid is called its
melting point.
• The temperature at
which a liquid
changes into a gas
is called its boiling
point.
Physical and Chemical Properties
1
Magnetic Properties
• Some materials pull iron toward them.
• These materials are said to be magnetic.
• Lodestone is a rock that is naturally
magnetic.
• Some materials can be made into magnets.
Physical and Chemical Properties
1
Chemical Properties
• Some properties of matter cannot be
identified just by looking at a sample.
• For example, the ability to burn is a
chemical property.
• A chemical property
is a characteristic that
cannot be observed
without altering the
substance.
Physical and Chemical Changes
2
Physical Changes
• A physical change is one in which the form
or appearance of matter changes, but not its
composition. For example, a frozen lake has
experienced a physical change.
• Although the water
changes states due to
change in temperature,
it is still made of the
elements hydrogen and
oxygen.
Physical and Chemical Changes
2
Changing Shape
• Crumpling a sheet of paper into a ball causes
a physical change.
• Whether it exists as one flat sheet or a
crumples ball, the matter is still paper.
• Generally, whenever you cut, tear, grind,
or bend matter, you are causing a physical
change.
Physical and Chemical Changes
2
Dissolving
• When you add sugar to iced tea, the sugar
only seems to disappear.
• Actually, the sugar dissolves.
• When this happens, the particles of sugar
spread out in the liquid.
• The composition of the sugar stays the same,
which is why the iced tea tastes sweet.
• Only the form of the sugar has changed.
Physical and Chemical Changes
2
Changing State
• A physical change occurs when matter
changes from one state to another.
• When an ice cube melts, for example, it
becomes liquid water.
• Matter can change from any state to another.
• Freezing is the opposite of melting.
• During freezing, a liquid changes into a solid.
Physical and Chemical Changes
2
Changing State
• A liquid also can change into
a gas. This process is known
as vaporization.
• During the reverse process,
called condensation, a gas
changes into a liquid.
Physical and Chemical Changes
2
Changing State
• In some cases, matter changes between the
solid and gas states without ever becoming
a liquid.
• The process in which a solid changes directly
into a gas is called sublimation.
• The opposite process, in which a gas changes
into a solid, is called deposition.
Physical and Chemical Changes
2
Chemical Changes
• The explosion of
fireworks is an example
of a chemical change.
• During a chemical
change, substances are
changed into different
substances.
• In other words, the
composition of the
substance changes.
Physical and Chemical Changes
2
Chemical Changes
• When iron in steel is exposed to oxygen and
water in air, iron and oxygen atoms combine
to form the principle component in rust.
• In a similar way,
silver coins tarnish
when exposed to
air.
Physical and Chemical Changes
2
Signs of Chemical Changes
• Physical changes are relatively easy to
identify.
• If only the form of a substance changes,
you have observed a physical change.
• How can you tell whether a change is a
chemical change?
Physical and Chemical Changes
2
Signs of Chemical Changes
• You have witnessed a spectacular chemical
change if you have seen the leaves on a tree
change from green to bright yellow, red, or
orange.
• But, it is not a change from a green pigment
to a red pigment, as you might think.
• Pigments are chemicals that give leaves
their color.
Physical and Chemical Changes
2
Signs of Chemical Changes
• The green pigment that you see during the
summer is chlorophyll (KLOHR uh fihl).
• In autumn,
however, changes
in temperature and
rainfall amounts
cause trees to stop
producing
chlorophyll.
Physical and Chemical Changes
2
Signs of Chemical Changes
• The chlorophyll already in the leaves
undergoes a chemical change into colorless
chemicals.
Physical and Chemical Changes
2
Signs of Chemical Changes
• The pigments that produce fall colors have
been present in the leaves all along.
• However, in the summer, chlorophyll is
present in large enough amounts to mask
these pigments.
• In the fall, when
chlorophyll
production stops,
the bright pigments
become visible.
Physical and Chemical Changes
2
Color
• The reason a half-eaten apple turns brown
is that a chemical change occurs when the
apple is exposed to air.
• The color of food changes as it is cooked
because a chemical change occurs.
Physical and Chemical Changes
2
Energy
• Another sign of a chemical change is the
release or gain of energy by an object.
• Many substances must absorb energy in
order to undergo a chemical change.
• For example, energy is absorbed during
the chemical changes involved in cooking.
Physical and Chemical Changes
2
Energy
• Another chemical change in which a
substance absorbs energy occurs during the
production of cement.
• This process begins with the heating of
limestone.
• When it absorbs energy during heating, it
undergoes a chemical change in which it
turns into lime and carbon dioxide.
Physical and Chemical Changes
2
Energy
• Energy also can be released during a
chemical change.
• Fireworks release energy in the form of light
that you can see.
Physical and Chemical Changes
2
Energy
• A chemical change within a firefly releases
energy in the form of light.
• Energy is released when sodium and chlorine
are combined and ignited.
• During this chemical change, the original
substances change into sodium chloride,
which is ordinary table salt.
Physical and Chemical Changes
2
Odor
• When eggs and other foods spoil, they
undergo chemical change.
• The change in odor is a clue to the chemical
change.
• When you smell an odd odor in foods, such as
chicken, pork, or mayonnaise, you know that
the food has undergone a chemical change.
• You can use this clue to avoid eating spoiled
food and protect yourself from becoming ill.
Physical and Chemical Changes
2
Gases or Solids
• The formation of a gas is a clue to a chemical
change.
• The formation of a solid is another clue to a
chemical change.
• A solid that separates out of a solution during
a chemical change is called a precipitate.
• A common precipitate forms when a solution
containing sodium iodide is mixed with a
solution containing lead nitrate.
Physical and Chemical Changes
2
Not Easily Reversed
• Physical and chemical changes are different
from one another.
• After solid ice melts into liquid water, it
can refreeze into solid ice if the temperature
drops enough.
• Freezing and melting are physical changes.
Physical and Chemical Changes
2
Not Easily Reversed
• The substances produced during a chemical
change cannot be changed back into the
original substances by physical means.
• Wood that has
changed into
ashes and gases
cannot be restored
to its original
form as a log.
Physical and Chemical Changes
2
Not Easily Reversed
• The substances that existed before the
chemical change no longer exist.
Physical and Chemical Changes
2
Chemical Versus Physical Changes
• In a physical change, the composition of a
substance does not change.
• In a chemical change, the composition of a
substance does change.
• When a substance undergoes a physical
change, only its form changes.
• In a chemical change, both form and
composition change.
Physical and Chemical Changes
2
Chemical Versus Physical Changes
• When substances like wood and copper
undergo physical changes, the original wood
and copper still remain after the change.
• When a substance undergoes a chemical
change, however, the original substance is
no longer present after the change.
Physical and Chemical Changes
2
Chemical Versus Physical Changes
• Instead, different substances are
produced during the chemical
change.
• When wood and copper undergo
chemical changes, wood and
copper have changed into new
substances with new physical
and chemical properties.
Physical and Chemical Changes
2
Chemical Versus Physical Changes
• Physical and chemical changes
are used to recycle or reuse
certain materials.
Physical and Chemical Changes
2
Conservation of Mass
• During a chemical change, the form or the
composition of the matter changes.
• The particles within the matter rearrange to
form new substances, but they are not
destroyed and new particles are not created.
Physical and Chemical Changes
2
Conservation of Mass
• The number and type of particles remains
the same.
• As a result, the total mass of the matter is
the same before and after a physical or
chemical change. This is known as the law
of conservation of mass.
Physical and Chemical Changes
2
Conservation of Mass
• In many chemical changes
in which mass seems to be
gained or lost, the difference
is often due to a gas being
given off or taken in.
• If the gases could be
contained in a chamber
around the candle, you
would see that the mass
does not change.
Physical and Chemical Changes
2
Conservation of Mass
• The scientist who first performed the careful
experiments necessary to prove that mass is
conserved was Antoine Lavoisier (An twan .
luh VWAH see ay) in the eighteenth century.
• It was Lavoisier who recognized that the
mass of gases that are given off or taken
from the air during chemical changes
account for any differences in mass.
Section Check
1
Question 1
An example of a size-independent property is
_______.
A. density
B. mass
C. volume
D. wattage
Section Check
1
Answer
The answer is A. A block of wood three times
the size of another block of wood does not
need to be denser. It must, however, have a
greater volume.
Section Check
1
Question 2
A tennis ball and a billiard ball may be the
same size, but they will definitely NOT have
the same _______.
A. density
B. parity
C. viscosity
D. width
Section Check
1
Answer
The answer is A. A billiard ball is denser than a
tennis ball.
Section Check
1
Question 3
Density is equivalent to mass divided by
_______?
Answer
The answer is volume. The formula for
determining density is D = m/V.
Section Check
2
Question 1
Any change in size, shape, form, or state is
known as a _______?
A. chemical change
B. chemical property
C. physical change
D. physical property
Section Check
2
Answer
The answer is C. In physical changes, the
identity of the substance in question remains
the same throughout.
Section Check
2
Question 2
A change from one type of matter to another is
known as a _______?
A. chemical change
B. chemical property
C. physical change
D. physical property
Section Check
2
Answer
The answer is A. In a chemical change the
identity of the substance itself is altered.
Section Check
2
Question 3
Explain the law of the conservation of mass.
Answer
The law of the conservation of mass says that
the total mass will be the same before and after
a chemical or physical change. Mass cannot
disappear, and no mass is created.
Table of Contents
Chapter 2: Elements of Chemistry
Section 2.1: Matter has Physical and Chemical
Properties & Changes
Section 2.2: Atoms are the Fundamental
Components of Elements
Section 2.3: Atoms can combine to Form
Compounds
Section 2.4: Most materials are Mixtures
Section 2.5: Chemists Classify Matter as Pure or
Impure
Section 2.6: Elements are Organized in the Periodic
Table by their Properties
Section 2.2: Atoms are the Fundamental
Components of Elements
• Chemists know of elements from atomic numbers 1 (hydrogen)
to 118 (ununoctium) have been discovered or reportedly
synthesized, with elements 113, 115, 117 and 118 having yet to
be confirmed. The first 98 elements exist naturally although
some are found only in trace amounts and were initially
discovered by synthesis in laboratories. Elements with atomic
numbers from 99 to 118 have only been synthesized, or claimed
to be so, in laboratories.
• These few 98 that are found in nature combine in different ways
to form all the substances in the universe.
Section 2.2: Atoms are the Fundamental
Components of Elements
• Element – any material consisting of only one
type of atom, ie: pure gold, nitrogen, carbon
• Periodic table – all these elements are listed in the
periodic table .
• Each element is designated by its atomic symbol,
ie: C for carbon, Cl for chlorine, Au for gold
(after its Latin name aurum), Pb for lead (Latin
name plumbum)
Section 2.2: Atoms are the Fundamental
Components of Elements
• Naming elements and compounds has
conventions.
• Elemental formula – how many elements are
bound together.
– Individual atoms – Au and Li
– 2 or more atoms bonded into molecules in their
natural state – N2, O2, S8
Table of Contents
Chapter 2: Elements of Chemistry
Section 2.1: Matter has Physical and Chemical
Properties & Changes
Section 2.2: Atoms are the Fundamental
Components of Elements
Section 2.3: Atoms can combine to Form
Compounds
Section 2.4: Most materials are Mixtures
Section 2.5: Chemists Classify Matter as Pure or
Impure
Section 2.6: Elements are Organized in the Periodic
Table by their Properties
Section 2.3: Atoms can combine to Form
Compounds
• Compound – when atoms of different elements
bond to one another, ie:
– Sodium and chlorine → sodium chloride
– Nitrogen and hydrogen → ammonia
• Chemical formula – a compound is represented
using symbols for the elements. They are
written together
– sodium chloride → NaCl
– Ammonia → NH3
Section 2.3: Atoms can combine to Form
Compounds
• The chemical formula for the compound
sodium chloride tell us that there is 1 sodium
atom for every one chlorine atom.
– sodium chloride → NaCl
• The chemical formula for the compound
ammonia tells us that there one nitrogen atom
for every 3 hydrogen atoms.
– Ammonia → NH3
Section 2.3: Atoms can combine to Form
Compounds
• Compounds have different physical and
chemical properties than their elemental
components.
– sodium chloride → NaCl
• Sodium – cut easily with knife, soft, silvery,
metal. M.p. is 97.5ᵒC, reacts violently w/ water
• Chlorine – yellow-green gas, toxic, used a
chemical warfare agent in WWI
• NaCl – translucent, brittle, colorless crystal,
not toxic, essential to living organisms, salty
Section 2.3: Atoms can combine to Form
Compounds
• Compounds are named according to the elements
they contain.
• International Union for Pure and Applied
Chemistry (IUPAC) developed naming system
which is very intricate.
• Three guidelines that are important in naming
most simple compounds consisting of 2 elements
and many other more complex compounds.
Section 2.3: Atoms can combine to Form
Compounds
• Guideline 1 – The name of the element farther to the L
in the P.T. is followed by the name of the element farther
to the R, with the suffix –ide added to the end.
NaCl – Sodium chloride
HCl – Hydrogen chloride
Li2O – Lithium oxide
CaF2 – Calcium fluoride
MgO – Magnesium oxide
Sr3P2 – Strontium phosphide
Section 2.3: Atoms can combine to Form
Compounds
• Guideline 2 – When 2 or more non-metal compounds
have different numbers of the same elements, prefixes
are added to remove ambiguity.
–
–
–
–
–
One – mono
Two – di
Three – tri
Four – tetra
Five – penta
CO – Carbon monoxide
CO2 – Carbon dioxide
SO3 – Sulfur trioxide
N2O4 – Dinitrogen tetroxide
PCl5 – Phosphorous pentachloride
Section 2.3: Atoms can combine to Form
Compounds
• Guideline 3 – Many compounds are referred to by
common names, not their systematic names.
– Water – dihydrogen oxide
– Ammonia – Trihydrogen nitride
– Methane – Tetrahydridocarbon
– Pteroenone – 5(S)-methyl-6(R)-hydroxy-7,9-dimethyl-7,9diene-4-undecanone
Table of Contents
Chapter 2: Elements of Chemistry
Section 2.1: Matter has Physical and Chemical
Properties & Changes
Section 2.2: Atoms are the Fundamental
Components of Elements
Section 2.3: Atoms can combine to Form
Compounds
Section 2.4: Most materials are Mixtures
Section 2.5: Chemists Classify Matter as Pure or
Impure
Section 2.6: Elements are Organized in the Periodic
Table by their Properties
Section 2.4: Most materials are Mixtures
• Most materials are mixtures of: elements, compounds
or both.
– Stainless steel – iron, chromium, nickel, carbon
– Seltzer water – water, carbon dioxide
– Earth’s atmosphere – nitrogen, oxygen, argon, carbon
dioxide, water vapor
– Tap water – compounds of water, calcium, magnesium,
fluorine, iron, potassium, chlorine, sulfur, lead, mercury,
cadmium, dissolved oxygen, nitrogen, carbon dioxide
Section 2.4: Most materials are Mixtures
Separating Mixtures
• Some can be separated easily by physical
means: rocks and marbles, iron filings and
sulfur (use magnet)
• Distillation - differences in physical properties
can be used to separate mixtures – m.p. & b.p.
• Filtration - separates a solid from the liquid in
a heterogeneous mixture (by size) – filter
paper
Section 2.4: Most materials are Mixtures
Distillation: takes advantage of
different boiling points.
NaCl boils at
1415 oC
Section 2.4: Most materials are Mixtures
Components of dyes such as ink may be
separated by paper chromatography.
Table of Contents
Chapter 2: Elements of Chemistry
Section 2.1: Matter has Physical and Chemical
Properties & Changes
Section 2.2: Atoms are the Fundamental
Components of Elements
Section 2.3: Atoms can combine to Form
Compounds
Section 2.4: Most materials are Mixtures
Section 2.5: Chemists Classify Matter as Pure or
Impure
Section 2.6: Elements are Organized in the Periodic
Table by their Properties
Section 2.5: Chemists Classify Matter as
Pure or Impure
• Pure – single element – pure gold
• Impure – mixture with two or more elements
or compounds
– Heterogeneous – the mixture is not uniform in
composition
• Chocolate chip cookie, gravel, soil.
– Homogeneous - same composition throughout;
called “solutions”
• Kool-aid, air, salt water
• Every part keeps it’s own properties.
Section 2.5: Chemists Classify Matter as
Pure or Impure
• Solutions and suspensions are homogeneous
mixtures
– Solution – all components in same (single) phase –
air, salt water, white gold
– Suspension – different components are in different
(2 or more phases) phases such as solids in liquids,
liquids in gases, etc. – milk, blood, clouds
• Spin in a centrifuge to distinguish between
solutions and suspensions.
Compound vs. Mixture
Compound
Mixture
Made of one kind
of material
Made of more than
one kind of material
Made by a
chemical change
Made by a
physical change
Definite
composition
Variable
composition
Elements vs. Compounds
• Compounds can be broken down into
simpler substances by chemical means,
but elements cannot.
• A “chemical change” is a change that
produces matter with a different
composition than the original matter.
Table of Contents
Chapter 2: Elements of Chemistry
Section 2.1: Matter has Physical and Chemical
Properties & Changes
Section 2.2: Atoms are the Fundamental
Components of Elements
Section 2.3: Atoms can combine to Form
Compounds
Section 2.4: Most materials are Mixtures
Section 2.5: Chemists Classify Matter as Pure or
Impure
Section 2.6: Elements are Organized in the Periodic
Table by their Properties
Section 2.6: Elements are Organized in the
Periodic Table by their Properties
• Elements organized in periodic table based on
physical and chemical properties.
• Metals – most of known elements
–
–
–
–
–
–
Shiny
Opaque
Good conductors of electricity and heat
Malleable
Ductile (drawn into wires)
Most are solids at room temperature
Section 2.6: Elements are Organized in the
Periodic Table by their Properties
• Elements organized in periodic table based on
physical and chemical properties.
• Nonmetals – on right side of PT (except H)
–
–
–
–
–
–
–
Brittle
Shatter when hammered
Transparent
Poor conductors of electricity and heat
Not malleable
Not ductile (drawn into wires)
At room temperature may be solid, liquid or gas
Section 2.6: Elements are Organized in the
Periodic Table by their Properties
• Elements organized in periodic table based on
physical and chemical properties.
• Metalloids – 6 elements (B, Si, Ge, As, Sn, Sb)
– Between metals and nonmetals on PT
– Properties of both metals and nonmetals
– Weak conductors of electricity and heat (good
semiconductors for integrated circuits)
– Ge – closer to metallic side so more metallic
properties – integrated circuits with Ge operate
faster than those with Si but Si more abundant
Section 2.6: Elements are Organized in the
Periodic Table by their Properties
• Elements organized in periodic table by
horizontal rows and vertical columns
• Row – called a period
• Column – called a group
• Periodic trends – called periodicity
– Atomic size decreases going L to R
Section 2.6: Elements are Organized in the
Periodic Table by their Properties
• Columns – properties of elements tend to be similar,
grouped in families.
– Group 1 - Alkali metals - from Arabic word al-qali, ashes,
ashes mixed with water produce a slippery solution that
removes grease
– Group 2 - Alkaline-earth metals – fire-resistant substances
known to ancient alchemists as “earth”
– Group 16 – Chalcogens – from Greek “ore-forming”
– Group 17 – Halogens – from Greek “salt-forming”
– Group 18 – Noble gases – unreactive gases that tend not to
combine with other elements, nobility did not interact with
common folk
Section 2.6: Elements are Organized in the
Periodic Table by their Properties
• Columns – properties of elements tend to be similar,
grouped in families.
– Groups 3 – 12 – Transition metals – harder than alkali
metals, do not form alkaline solutions with water, less
reactive with water
– Inner transition metals – 6th and 7th periods of PT
– Sixth period – Lanthanides – fall after lanthanum, tend to
occur mixed together in the same locations in the Earth
• Difficult to purify
• LEDs
– Seventh period – Actinides – fall after actinium,
• Difficult to purify
• Uranium and plutonium