The Chemical Nature of Matter
7th Grade Science
Standard 7-5
Classification of Matter


Matter is something that has mass and takes up
space
It can be classified by what it is made of
(composition)
Solids
Take
up Space
Have a fixed shape
Don’t flow
Have weight
LIQUIDS
Takes
Up Space
CHANGE Shape to fit
container
 Flow
Have weight
Gases
Takes
up Space
Change Shape
Invisible (usually)
Have weight
Atoms
Atoms – the smallest part of an element that
has chemical properties of that element
 Has mass and takes up space

Pure substances - Elements

Elements – pure
substances that cannot
be changed into
simpler substances,



Ex. Iron, hydrogen,
oxygen, calcium
Elements are composed
(made) of only one type
of atom.
Elements are
represented by
symbols:
Element
Symbol
Sodium
Na
Chlorine
Cl
Hydrogen
H
Oxygen
O
Carbon
C
Nitrogen
N
Mixtures
Mixtures are composed of two or more different
substances that retain their own individual properties and
are combined physically (mixed together).
Mixtures can be separated by physical means (filtration,
sifting, or evaporation).
Mixtures may be heterogeneous (DIFFERENT) or
homogeneous (SAME).
Compounds
Compounds are pure substances that are
composed of two or more types of elements
that are chemically combined.
Compounds can only be changed into simpler
substances called elements by chemical
changes (7-5.10).
One way that two or more atoms can combine
is to form a molecule.
MATTER ACTIVITY
Periodic Table
Periodic Table of the Elements – a chart
that organizes all of the elements
 Elements of the periodic table are identified
with numbers (called atomic numbers)
increasing from left to right across each row.

Periodic Table Cont.
A horizontal row is called a period
 The periodic table has a square for
each element with the atomic
number, atomic mass, element
name, and the element symbol

Atomic number
Element name
Element symbol
Atomic mass

There are two large sections of the table.
Find the zigzag line – on the left are metals
and on the right of that line are non-metals
Families of the Periodic Table

Families – also called
groups, vertical columns of
elements that have similar
properties
Metals

Metals –Groups of elements
generally located on the left
side of the zig zag line of the
table
Ex. Sodium (Na), Calcium
(Ca), Iron (Fe), and Aluminum
(Al)
 Have the following properties
in common - luster, are
conductors, are malleable,
ductile and have high density

Luster

Luster – shiny surface, reflecting light
brightly

ex. Aluminum (inside of a soda can)
Properties of Metals

Conductors – heat and electricity move through
them easily


Malleable – ability to be hammered into different
shapes


Ex. Gold
Ductile – ability to be drawn into wire


Ex. Copper wire, aluminum pot
Ex. Wire
High Density – heavy for their size

Ex. Bar of silver
Nonmetals

Nonmetals – Groups of elements generally
located on the right side of the table


Ex. Chlorine (Cl), Oxygen (O), Sulfur (S), and
Iodine (I)
Have the following properties in common are dull, nonconductors and are brittle.
Properties of Nonmetals
Dull – not shiny
 Nonconductors – heat and electricity do no
move through them
 Brittle – break or shatter easily

Chemical Symbols

Elements have chemical symbols.
Chemical Symbols
Na - Sodium
Cl - Chlorine
H - Hydrogen
O - Oxygen
C - Carbon
N - Nitrogen
Compound
Compounds – pure substances that are
composed of two or more types of elements
ex. Water, salt, sugar
 Can only be changed into simpler
substances (elements) by chemical
changes.

Mixtures
Mixtures – composed of different
substances that are mixed together
 Ex. Italian dressing, garlic salt,
iron filings and sulfur (pictured here)
 Mixtures can be easily separated into their
component substances by filtering, sifting,
magnetic attraction, evaporation,
chromatography and flotation.

Chemical Formulas
Compounds and some forms of elements
have chemical formulas.
 Molecule - The smallest part of a
compound.
 Chemical Formulas
H2O
- Water
CO2
- Carbon Dioxide
NaCl
- Sodium Chloride (or salt)
C6H12O6
- Simple Sugar

Diatomic Molecules

Some elements bond together to be more
stable, the next two formulas are for diatomic
(two atom) molecules. These occur
abundantly in earth’s atmosphere.
O2 - Oxygen gas*
 N2 - Nitrogen gas*

Solutions
Solutions – a liquid (ex. Water = solvent)
that has something dissolved in it ex. Sugar
(solute)
 Concentration – the amount of solute in a
solution

pH
pH – a measure of the concentration of
solutions of acids and bases
 Stands for “power of Hydrogen” or how
many hydrogen ions are in a liquid
 The pH scale goes from 1-14. 1 being the
strongest acid, 14 being the strongest base,
7 being neutral.
 Water (non-polluted or distilled) should be
neutral.
pH Scale
The pH scale goes from 1-14. 1 being the
strongest acid, 14 being the strongest base,
7 being neutral.
 Water (non-polluted or distilled) should be
neutral.

Acids
Acids – 0-6 on the pH scale
 Have a sour taste ex. Lemon, orange
 NEVER use the taste test on laboratory
chemicals
 Reacts with metals (see evidence for a
chemical reaction below)
 Reaction with bases to form neutral pH
solutions

Bases
Bases – 8-14 on the pH scale
 Bitter taste ex. Soapsuds
 NEVER use the taste test or feel test on
laboratory chemicals
 Feel slippery ex. Chlorox, liquid soap
 Reaction with acids to form neutral pH
solutions

Neutral
Neutral – neither an acid nor a base
 Water (non-polluted or distilled) should be
neutral

pH Scale
Indicators

Indicators – substances that can be used to
determine whether a solution is an acid or a
base
Litmus Paper
 pH Paper
 Phenolphthalein

Litmus Paper
Litmus paper –
 blue litmus paper turns red in an acid and
stays blue in a base
 red litmus paper turns blue in a base and
stays red in an acid
 Both red and blue litmus paper turn purple in
a solution that is neutral
 Usually neither turn a color – just get wet
paper.

Litmus Paper

*Always use a strip of red and blue paper
when testing a substance. You need the
results of both to compare to be sure you
have an acid, base or neutral!
pH Paper & Phenolphthalein
pH paper – can turn a series of colors, the
color of the paper is compared to the chart
on the pH paper vial to determine the pH
 Phenolphthalein – turns magenta (hot pink)
in a strong base and stays clear in an acid

Chemical Equations

Chemical Equations – are used to
represent chemical reactions, they contain
the chemical formulas for the substances
that are mixed and the new substance(s)
that are formed. An arrow separates them.
Chemical Equations
Reactants – the substances that are mixed
in a chemical reaction, are on the left side of
the arrow
 Products – the new substance(s) that are
formed in a chemical reaction, are on the
right side of the arrow

Law of Conservation of Matter
Law of Conservation of Matter – matter is
neither created nor destroyed, but can be
changed in form
 The amount of matter does not change
during a chemical reaction; only the atoms
are rearranged to form new substances.
 The total mass of the material(s) before the
reaction is the same as the total mass of
material(s) after the reaction
Balanced Chemical Equations

Balanced chemical equations – A
balanced chemical equation has the same
number of each kind of atom on both sides
of the arrow.
Physical Properties

Physical Properties – properties that can
be observed and measured without
changing the kind of matter being studied
Color
 Melting Point
 Boiling Point
 Density

Color & Melting Point
Color – can be distinctive and can be used
to help identify a substance
 Melting point – temperature at which a solid
can change to a liquid

Boiling Point & Density
Boiling point – temperature at which a
liquid changes into a gas
 Density – the measure of the “heaviness”
of objects with constant volume, the mass of
a given volume of a substance

1 mL H2O = 1cm3 H2O = 1 g H2O
 Density of water = 1 g/mL or 1 g/cm3 or 1g/cc

Chemical Properties

Chemical Properties – properties that are
not always visible, can be recognized only
when substances react chemically with one
another
Chemical reactivity is the tendency of a
substance to undergo a chemical reaction
usually with other specific substances
 Burning - When a substance reacts with oxygen
quickly and releases heat and light energy

Chemical Properties
Rusting – when a substance reacts with
oxygen and water slowly

Ex. iron

Physical Changes
Physical Changes – DO NOT change the
identity of the substance
 Change of state (solid to liquid to gas)
Ex. Ice to water
 Change in shape like tearing or shredding
Ex. Paper
 Change in size like when crushing
Ex. chalk
Chemical Changes

A Chemical Change – changes the identity
of the substance

Ex. Na -Sodium is a highly reactive metal – it
explodes when placed in water
Cl – Chlorine is a poisonous gas
When they combine in a chemical reaction they
make NaCl – salt – basically a harmless
substance
Zip Lock Bag Chemistry
Activity

Can you identify the evidence of a chemical
reaction?
How can you tell a chemical
change has happened?
Evidence of a chemical reaction or
chemical changes:
 Color change – when a substance changes
color the chemical composition usually
changes
 Temperature change – When
substances change temperature
after being mixed with other substances
Evidence of Chemical Change

Precipitate formation – when two or more
liquids are mixed and a solid (precipitate) is
forms

Gas formation – when two or more
liquids are mixed or heated and a
gas (bubbles) is given off