Chapter 2: Introduction to Matter (plus graphing)
Graphing
Bar (histograms) and line (scatter plot) graphs
Make an x-axis (horizontal) and a y-axis
(vertical) on your graph that will
represent the variables of your
experiment
The x-axis represents the independent
variable or the manipulated variable
whose values are chosen by the
experimenter
The y axis represents the dependent
variable or the responding variable
Choose an appropriate scale for each axis
making sure there will be evenly spaced
intervals that include all your data and
that the label includes the units when
they apply
Plot your data on the graph and double
check your work and numbers for
accuracy.
Always write a title for your graph; one
that clearly identifies what information
is being graphed and that explains the
relationship between the variables
SI prefixes
giga
mega
kilo
hecto
deka
G
M
k
h
da
deci
centi
milli
micro
nano
d
c
m
μ
n
1 000 000 000.
1 000 000.
1 000.
100.
10.
1.
0.1
0.01
0.001
0.000 001
0.000 000 001
Example: Convert 11 000 mm into km
Moving up the table from mm to km is six steps, so we must move the decimal six places
Also notice that the ‘1’s are moving to the left going up, so the decimal moves to the left
0 1 1 0 0 0 . mm or 0.011 km
Measuring matter and Système International (SI)
Weight and Mass
Weight: a measure of the force of gravity acting on an object
If you weigh 88 lbs on Earth, you will weigh about 15 lbs on the moon
Mass: a measure of the amount of matter that composes an object
If you have a mass of 40 kg on Earth, you will have a mass of 40 kg on the moon
Units of mass: the kilogram (kg) – although most measurements in our lab will be in grams (g)
Volume and Density
Volume: the amount of space a sample of matter occupies
For regularly shaped solid objects, volume can be calculated by the formula:
V=hxlxw
(The unit for length is the meter, m, but cm and mm are also used)
Example: Find the volume of a block with sides measuring 9.5 cm by 7.5 cm by 15.0 cm
9.5 cm x 7.5 cm x 15.0 cm = 1068.75 cm3 or about 1100 cm3
For irregularly shaped solid objects, volume
is measured by water displacement
Example: Find the volume of the rock in the
diagram to the right
Volume of the water and the rock = 60.6 mL
- Volume of the water
= 54.5 mL
Volume of rock
= 6.1 mL
Units of volume: notice that there are two units used
The cubic centimeter, cm3 (sometimes cc)
The milliliter, mL
1 mL = 1 cm3
Density: the mass of a material in a given volume
Density
or D
Example: A small block of wood floats on water. It has a mass of 200 g and a volume of
250 cm3. What is the density of the wood?
Make your shopping list: (always use units, always list the quantity you are looking for)
m = 200 g
V = 250 cm3
D=?
From the list, it should be obvious we must use the density formula
m = 200 g
D =
3
V = 250 cm
D=?
Do all substitutions
m = 200 g
D =
V = 250 cm3
=
D=?
Solve the problem
m = 200 g
V = 250 cm3
D=?
D =
=
= 0.8 g/cm3
Check your work:
Are the units correct?
Does your answer make sense?
Yes, density units are g/cm3
Yes, 0.8 g/cm3 < 1 g/cm3, so the block would float
We noted that our answer made sense because it had a density less than that of water (1 g/cm3)
Things with lower densities will always float on liquids with higher densities
Because density is a physical property that does not change as the size of the sample changes,
it can be used to identify substances
Properties of matter
Chemistry: The study of the properties of matter and how matter changes
Matter: anything that has mass and takes up space
Substance: a single kind of matter that is pure – specific composition and a specific set of properties
Element: a substance that cannot be broken down by chemical of physical means
An element is composed of only one type of atom
Elements are the simplest substances
Compound: a substance made of two or more elements combined in a set ratio
When elements are combined they form compounds having properties that are different from those of
the uncombined elements
Compounds may be represented by a chemical formula (like H2O)
Compounds are difficult to separate into its elements by ordinary means
It is possible to decompose compounds using chemical means
Molecule: a group of atoms held together by a specific type of chemical bonds
Chemical bond: a force of attraction between atoms
Covalent bonds: form when electrons in a chemical bond are shared to form molecules
Mixture: composed of two or more substances (elements, compounds, or both) together in the same place
but are not chemically combined
Each substance in a mixture retains its individual properties
Mixtures are not combined in a set ratio
Heterogeneous mixtures: you can see the different parts
Gravel, salad, salt added to sand, granite
Homogeneous mixtures: are so evenly mixed, you cannot see the different parts
Elmer’s glue (a colloid) or salt dissolved in water (a solution)
Separating mixtures
Mixtures can be easily separated using ordinary physical means
This is accomplished by taking advantage of the different physical properties of the substances that
compose the mixture
Examples: magnetic attraction, solubility, filtration, distillation, evaporation, or chromotography
Properties: characteristics of a substance that can be used to help identify the matter
Physical properties: can be observed without changing the substance into another substance
Melting point, boiling point, hardness, density, or phase
Chemical properties: describe the ability of a substance to change into another substance
Flammability, reactivity, acidity, rusting, or tarnishing
Physical change: alters the form or appearance but does not change the chemical identity
Change of state: solid, liquid, or gas
Solutions: dissolving sugar in water
Change in form: bending, crushing, breaking, or chopping for example
Chemical change: a change in matter that produces one or more new substances or combines two or
more substances to form a new substance
Examples of chemical change: combustion, electrolysis, oxidation, and tarnishing
Law of Conservation of Mass: matter is neither created not destroyed during chemical or physical
changes
Discovered by Antoine Lavoisier (1770s) who made careful measurements before and after chemical
changes
Energy and Matter
Energy: the ability to do work
Energy comes many forms
Kinetic energy: the energy of matter in motion
Potential energy: the energy matter has because of its position or condition
Chemical energy: energy absorbed or released when chemical bonds are broken or formed
Electromagnetic energy: a form of energy that can travel through space in rays (or waves)
Electrical energy: the energy from movement of charged particles
Thermal energy: heat or energy that can be transferred from objects with a higher temperature to
objects with a lower temperature
Transforming Energy: energy can be transformed from one form to another
Electrolysis: using electrical energy to split compounds into elements
Electrical energy is transformed into chemical energy during this process
Peddling a bike is transforming chemical energy into kinetic energy
As you move the bike uphill, kinetic energy is being transformed into potential energy