Download Chemistry Essentials Unit 2

Chemistry Essentials
Unit 2
Matter – A Central Idea in Chemistry
Unit Warm-Up
1. What do chemists study?
2. How do atoms differ from molecules?
3. Describe a chemical change (chemical
reaction) you have witnessed outside of school.
How did you know that it was a chemical
change?
Section 1: The Nature of Matter
Chemists study matter
What it is
How it changes
Matter is the physical “stuff” the Universe is
made of
Examples: a tree, your body, atoms, water, air
All matter has two characteristics
Mass
Volume (takes up space)
Humans have studied matter forever
We ask the question “What is everything made
of?”
The simple answer is ---- MATTER
So…. What is matter made of?
Since ancient times two schools of
thought:
Aristotle (300’s BCE)
Fundamental set of substances that can be combined
to form all other substances
Called elements
Earth, air, fire, and water
Democritus (400’s BCE)
There is a fundamental particle all matter is made of
Called the atom
Who was right?
BOTH!
Matter is made of elements and elements are made of
atoms
Atoms
Fundamental particle from which elements are
made
~ 92 different types of atoms that occur
naturally in the Universe
Microscopic -- invisible to the naked eye
Elements
Substance that contains only 1 type of atom
Cannot be broken down into other substances
Macroscopic – can see with naked eye
Section 2: Pure Substances
Is all matter the same?
Of course not!!!!!
We can find similarities to create
types of matter
Can be classified into 2 broad categories
pure substances
mixtures
Pure Substances
Composition is the same throughout (contains
only 1 type of matter)
Can be an element or a compound
Examples: gold, water, baking soda,
oxygen
Elements
Contains only 1 type of atom
~ 92 naturally occurring elements
Cannot be broken down by ordinary means; must
use nuclear reaction
Symbol has only 1 capital letter
Examples
copper (Cu), carbon (C), lithium (Li), tungsten(W)
Macroscopic idea (microscopic is atom)
Compounds
Contain two or more types of atoms that are hooked
together by a chemical bond
Infinite number of compounds possible
Ratio of atoms is always the same
Cannot be separated into elements by physical
means; must use chemical means
Properties are very different from properties of
elements that it is made of
Formula has more than 1 capital letter
Macroscopic idea (microscopic is molecule)
Examples
CH3OH -- methanol
H2O – water
NaCl – sodium chloride (table salt)
Examples
Identify the following as an element or a compound
a)Mg
element
b) CuSO4
compound
c) Zr
element
d) P
element
e) I2
element
f) C6H5OH
compound
Separating Compounds
Must be separated by chemical means (break the
chemical bonds)
Example
Electrolysis
Passing an electric current through the compound will
break the bonds
Water – H2O will be broken down into H2(g) and O2(g)
Practice
Identify each of the following as an element or a
compound:
a) Au
element
b) C6H12O6
compound
c) KMnO4
compound
d) Pb
element
Section 3: Mixtures
Two or more substances that occupy the same container
without interacting with each other
No chemical bonds between components of the mixture
Variable composition from sample to sample or within a
sample
Properties are usually a blend of the properties of the
components in the mixture
No definite formula
May contain elements, compounds, or both
May contain solids, liquids, &/or gases
Can be separated by physical means (sorting,
filtration, chromatography, etc.)
Examples; soda, dirt, sand, coffee, air
Types of mixtures
Mixtures can be classified as either homogenous
mixtures or heterogeneous mixtures
Homogeneous Mixtures
Same throughout – cannot see the different
substances that make up the mixture
May also be called solutions or alloys
Examples: chocolate milk, brewed tea, salt water,
air, brass
Heterogeneous Mixtures
Not the same throughout – can see at least two
substances in the mixture
May have different properties in different
regions of the mixture
Examples: a bag of M&M’s, sand and water, iced tea
Examples
Identify each of the following as a homogeneous
mixture or a heterogeneous mixture
a) brewed coffee
homogeneous mixture
b) a glass of Coke with ice
heterogeneous mixture
c) a bag of Skittles
heterogeneous mixture
d) Gatorade
homogeneous mixture
Practice
Identify each of the following as a homogeneous
mixture or a heterogeneous mixture.
a) Gasoline
homogeneous mixture
b) A stream with gravel at the bottom
heterogeneous mixture
c) Air
homogeneous mixture
d) A bowl of Lucky Charms cereal with milk
heterogeneous mixture
Section 4: Properties of Matter and
Changes in Matter
Chemistry is about
Matter and its changes
Describing Matter
How to describe matter?
List its properties
Property—an observable characteristic
of matter
Properties are either microscopic or
macroscopic
Two types of macroscopic properties
Physical properties and chemical properties
Physical Properties
Describe matter on its own
Does not require matter be changed into
a different type of matter
Still the same substance after
determining the property
Examples: color, odor, texture, shape, state
at a given temperature, density, melting
point, boiling point
States of Matter
Substances can exist in one of three states of
matter under normal conditions
Solid
Liquid
Gas
States are temperature and pressure dependent
Macroscopic reflection of microscopic particle
movement and relative position
Solids
Low temperature &/or high pressure
Microscopically:
Particles are close together
Minimal movement – only vibrations
Lots of inter-particle interactions
Macroscopically
Observed as having fixed shape and volume
Ice (solid form of water)
Liquids
Higher temperatures &/or lower pressure
Microscopically
Particles slightly apart from each other
Some movement present – sliding
Some inter-particle interactions
Macroscopically
Observed as having definite volume but not
shape – will take shape of container
Liquid water
Gases
High temperature &/or low pressure
Microscopically
Particles are very far apart from each other
Lots of particle movement – all directions
Almost no inter-particle interactions
Macroscopically
Observed as having no definite shape or
volume – will fill the container
Water vapor
Chemical Properties
Describe how matter interacts with other matter
to form new substances
What happens when it combines with____?
Examples: Does it combine with oxygen to form a new
substance?
The matter is a different substance after observing
the property
How to tell if it’s a physical or
chemical property?
Ask question
Is this the same substance as before I observed it?
If yes – it’s a physical property
If no – it’s a chemical property
Example
Classify each of the following as a physical or a
chemical property:
a) a certain solid melts at 2000ºC
Physical Property
b) when combined sodium metal and chlorine
gas turn into sodium chloride (table salt)
Chemical property
Practice
Classify each of the following as a physical or a
chemical property:
a) The boiling point of a certain alcohol is 78C
physical
b) Diamonds are very hard
physical
c) Sugar ferments to become alcohol
chemical
d) A metal wire conducts electric current
physical
Changes in Matter
There are two types of changes
Physical changes
Do not involve the matter changing
into a new substance
Chemical changes
Require the matter to change into
something new with different
properties
Physical Changes
Do not involve the matter changing into a new
substance
Microscopically: No bonds are broken or
formed.
Indicators ( Macroscopically)
Change in size or shape
Change in state
Dissolving and recrystallization
Expected color change
If only 1 substance involved – physical change
Chemical Changes
Require the matter to change into something new
with different properties
Microscopically: Bonds are broken &/or formed)
Indicators(Macroscopically)
Unexpected color change
Formation of a solid from two or more liquids or gases
Formation of a gas, not due to boiling
Production or absorption of heat
Production of light
Must be at least two substances involved
Examples
Classify each of the following as a physical
change or a chemical change and give a
reason for your answer
a) A white crystalline solid is crushed to a fine
white powder.
Physical change – change in size
b) Two clear colorless liquids are mixed and the
resulting mixture is orange.
Chemical change – unexpected color change
c) A piece of paper is crumpled.
Physical change – change in shape
Practice
Classify each of the following as a physical change or a chemical change and give a
reason for your answer.
a)
A green crystalline substance is placed in a mortar and ground to a fine green
powder.
physical change – change in size or shape
b) A clear blue liquid and clear yellow liquid are mixed. The resulting liquid is clear
and green.
physical change – expected color change
c) A small piece of a white solid is placed in a flask and a clear colorless liquid is
added. The white solid bubbles vigorously and eventually disappears, leaving a
colorless liquid in the flask.
chemical change – formation of a gas, not due to boiling
d) Two clear colorless liquids are mixed in a flask and the flask becomes cool to the
touch.
chemical change – absorption of heat
e) A blue solid is mixed with a clear colorless liquid until no solid remains. The liquid
is then heated and the blue solid reappears.
physical change – dissolving and recrystallization