IES MACARENA
PHYSICS AND CHEMISTRY 2º ESO
UNIT 2. CLASSIFICATION OF MATTER.
(Numbers are not written in English notation, so decimals are expressed with commas instead of points)
1. MACROSCOPIC AND MICROSCOPIC SCALES.
Microscopic scale is the scale of objects that cannot be seen by the naked eye. For example:
a bacterium, a molecule or an atom.
Macroscopic scale is the scale of objects that can be seen by the naked eye. For example: a
tree, a meteorite or a planet.
2. SCIENTIFIC NOTATION.
Writing an atom diameter’s value needs numbers with many zeros. The same happens with the
Universe’s diameter. Both large and small numbers can be expressed as a number between 1
and 10 times 10 raised to some power.
METHOD OF WRITING LARGE NUMBERS
The power of ten tells you how far to move the decimal point to the right. For example:
2 553 000 = 2,553·106
(You have to move six places the decimal point)
METHOD OF WRITING SMALL NUMBERS
Look at the following powers of ten:
0,1 =
1
101
1
0,01 =
=
102
100
= 100-1 = 10-1 ;
101
100
=
102
= 100-2 = 10-2 ;
0,001 =
1
103
=
100
103
= 100-3 = 10-3
The power of ten tells you how far to move the decimal point to the left. For example:
0,0000324 = 3,24·10-5
(You have to move five places the decimal point)
LIST OF PREFIXES IN THE SI
24
10
1021
1018
1015
1012
109
106
103
102
101
Prefix
Yotta
Zetta
Exa
Peta
Tera
Giga
Mega
Kilo
Hecto
Deca
Symbol
Y
Z
E
P
T
G
M
K
H
Da
Name
Septillion
Sextillion
Quintillion
Quadrillion
Trillion
Billion
Million
Thousand
Hundred
Ten
-24
10
10-21
10-18
10-15
10-12
10-9
10-6
10-3
10-2
10-1
Prefix
Yocto
Zepto
Atto
femto
Pico
nano
micro
Mili
centi
deci
Y
Z
A
F
P
N

M
C
D
Name
Septillionth
Sextillionth
Quintillionth
Quadrillionth
Trillionth
Billionth
Millionth
Thousandth
Hundredth
Tenth
(billion = mil millones; trillion = billón; quadrillion = mil billones; quintillion = trillón; etc.)
3. CLASSIFICATION OF SUBSTANCES
3.1 PURE SUBSTANCES: SIMPLE SUBSTANCES AND COMPOUNDS
A pure substance has specific properties and a uniform composition. Water, iron, sodium
chloride and diamond are pure substances. A substance made up of two or more pure
substances is called a mixture. Salt water (salt and water) and air (oxygen, nitrogen, water
vapor and other gases) are mixtures.
Simple
There are two kinds of pure substances: simple substances and compounds.

Simple substances are made up of atoms of only one element. For example: hydrogen,
gold, iron, silver, nitrogen.

Compounds are made up of atoms of two or more elements. For example: water,
ammonia, sodium chloride, methane, butane.
3.2 MIXTURES: HOMOGENEOUS AND HETEROGENEOUS MIXTURES

Heterogeneous mixtures: are those whose components we can see with the naked
eye or with a microscope. Their properties vary from one point of the mixture to another.
For example, granite or water with oil.

Homogeneous mixture or solutions: are those whose components we can’t see with
the naked eye or a microscope. Their properties are the same at every point of the
mixture. For example, air or water with sugar.
3. CHEMICAL AND PHYSICAL CHANGES.
In a chemical change new substances are formed. Iron rusting, gasoline burning are chemical
changes.
In a physical change no new substances are formed. Every change of state (melting,
solidification, condensation, sublimation, etc.) is a physical change.
QUESTION 1: Which one do you think is a reversible change, a chemical or a physical change?
QUESTION 2: If you separate water from sand by filtering, is it a chemical or a physical change?
Why?