Transcript What is matter?

Lecture 1: chemistry, measurement, conversions
Topic
Brown Chapter 1
1. Science and Chemistry
What is science?
The scientific method
What is chemistry?
1.1
2. What is matter?
1.2
States of matter
Pure substances vs. mixtures
Physical vs. chemical change
1.3
3. Measurement, metric units & prefixes
1.4
Derived units and density
Exact & inexact numbers
Uncertainty, precision & accuracy
1.5
Significant figures & use in calculation
Scientific notation
4. Dimensional analysis = conversions
1.6
With multiple conversion factors
Conversions with unit prefixes
With cubed unit volumes
Matter takes has mass & volume;
it occupies space.
Matter has energy-dependent physical states.
Matter can be a pure substance or a mixture.
Matter undergoes physical or chemical change.
What’s this “matter” that chemists study?
Matter?
The physical stuff of the universe; anything that has mass & occupies
volume or space.
All matter is found in one of three physical states:
p.4-9
Energy content determines physical state.
What does it take to convert from one form to the other?
abundance?
Gas?
Liquid?
Solid?
energy?
low
high
medium
medium
high
none/low
shape?
compression?
indefinite
indefinite
fixed
possible
difficult
not possible
What happens to physical state when:
1. Temperature is increased or decreased?
Increased: solid -> liquid -> gas
2. Pressure is increased or decreased?
Increased: gas -> liquid -> solid
p.4-9
Pure substances
Pure Substance?
Matter with distinct properties and composition - does not vary from
sample to sample.
…. Examples?
There are two types of pure substance:
1. Elements Cannot be decomposed into simpler substances.
(Although it’s true that particle physicists can smash atoms
into subatomic particles.)
2. Compounds Substances created by combining two or more atoms at a
constant atomic ratio. So compounds can be broken down
(or decomposed) into simpler substances or atoms.
An example is the electrolysis of water.
Two identical atoms
a. diatomic
b. mixed atoms
Well…….
p.5-8
How many elements are there?
Currently, 117 elements.
And they’re all listed in the periodic table
Inside cover
Mixtures: varying ratios
Mixtures
Two or more substances combined at a varying ratio.
Note that most of the matter we see in daily life exists as mixtures.
Mixtures can be found in all three physical states.
Give me examples of mixtures in each state……
p.8-9
Homogeneous vs. heterogenous?
Mixtures are described using one of these terms.
Homogeneous (aka SOLUTIONS)
Uniform throughout, or “smooth”
Heterogeneous
Not uniform throughout, or “chunky”
p.8-9
Flowchart for describing matter
Get to know these
questions!
p.9
Physical properties of matter
Physical properties
Can be observed without changing the identity or composition of the
substance. Example: changes in physical state.
• color
• odor
• Density
• melting point
• boiling point
• freezing point
Intensive properties?
Are independent of the amount of a material being observed. They are innate,
inborn, inherent and unchanging characteristics of a substance. In fact, intensive
characteristics are often used to identify substances.
Extensive properties?
Depend on the amount of material being observed. There are really only two
extensive properties: mass & volume
p.9-11
Separating mixtures
Both physical & chemical properties of substances can be used to
separate mixtures into their component parts.
filtration
distillation
chromatography
p.11-12
Chemical properties of matter
Chemical properties
Describe how a substance may change or react to form other substances.
Chemical change
Transforms one substance into another.
Identity changes, but the atoms that make up substances aren’t changed,
atomic connections are just rearranged.
p.9-11
“Decomposition” of molecules
Decomposition:
The breakdown of molecules into smaller molecules or elements.
Electricity can break water down into hydrogen & oxygen gases.
[Note that electrolysis produces twice as
much hydrogen as oxygen.
Why?
Water molecules, H2O,
have two H atoms for
each O atom.]
p.7