2. WHAT IS CHEMISTRY?
Chemistry is the study of matter and the
transformations it undergoes.
What is matter?
– Anything that has mass and takes up space.
3. IMPORTANCE OF
CHEMISTRY
Chemistry is all around you.
– Air you breathe
– Food you digest
– Clothes you wear
– Textbook you read
Chemistry is often said to be the central
science.
4. SCIENCE V.S. TECHNOLOGY
How is science different from technology?
Science:
– Experimental investigation and exploration of natural
phenomena
– Pursues knowledge for its own sake
– Does not cause change in itself
Technology
– The practical application of scientific knowledge
– Leads to change (for better or for worse)
5. SCIENCE V.S. TECHNOLOGY
(Cont)
Examples of science:
– What causes the flu?
– How are atoms put together?
– How is genetic information stored and transmitted?
Examples of technology
– Flu vaccine
– Atomic bomb
– Genetic engineering
6. SCIENTIFIC METHOD
Step 1: Make observations
– Example: I am sick with a stomachache.
Step 2: Develop a hypothesis
– Example: I am sick due to the spoiled food I ate
for lunch.
Step 3:
Test hypothesis through
experiments
– Example: Ask others who ate the same food for lunch
if they got sick.
7. SCIENTIFIC METHOD (Cont)
Step 4: Develop a law
– Law: Summarizes the outcome of several
experiments that occur repeatedly and consistently.
– Example: The spoiled food served at lunch makes
people sick with a stomachache.
Step 5: Develop a theory
– Theory: Explanation for a why a law exists.
– Example: It is the bacteria in the spoiled food that
makes people ill.
8. SCIENTIFIC METHOD (Cont)
Theories
– Are never completely certain
– May change as more experiments are
performed.
– A model is a physical picture or mathematical
expression of a theory.
Example: Model of the atom
The scientific method must be free of bias.
10. ELEMENTS
Elemental substances contain only one
type of atom
Elements are the building blocks of
matter
There are 115 known elements today, 90
which occur naturally
The periodic table displays the elements
11. ELEMENTS (Cont)
Each element has a unique symbol
– The first letter is always capitalized, the
second letter is always lower case
Fluorine is F, not f
Cobalt is Co, not CO (which is carbon monoxide)
The smallest unit of an element is the
atom
12. COMPOUNDS
Pure substances containing more than one
different element.
– NaCl (table salt)
Contains sodium (Na) and chlorine (Cl)
NaCl is the chemical formula
– H2O (water)
Contains 2 atoms of hydrogen (H) and 1 atom of oxygen (O)
H2O is the chemical formula
Elements in compounds are combined in a
definite ratio
– H2O is water but H2O2 is hydrogen peroxide
14. CLASSIFICATION OF MATTER
Classify the following as an element,
compound, homogeneous mixture, or
heterogeneous mixture.
a. Fog
b. Gasoline
c. Helium
d. Sulfuric acid (H2SO4)
e. Orange juice from squeezed oranges
17. CHANGES IN STATE
Melting: Solid to liquid
Boiling: Liquid to gas
Sublimation: Solid to gas
– The above three require input of energy
Condensation: Gas to liquid
Freezing: Liquid to solid
Deposition: Gas to solid
– The above three release energy
18. PHYSICAL CHANGES
Do not alter the chemical identity of the
substance
– Examples include:
Any change in the state of matter (e.g. freezing or
boiling water)
Sawing wood
Crushing a tablet
Bending a wire
Dissolving salt in water
19. PHYSICAL PROPERTIES
Characterize the physical state and
physical behavior of a substance
Each substance has unique physical
properties
Examples
– Sulfur appears as a yellow powder
– The boiling point of water is 100 oC
– Carbon monoxide is odorless
20. CHEMICAL CHANGES
Changes the identity of the substance as
the chemical composition changes.
– Also called chemical reactions
Examples:
– Tarnishing of silver
(Ag forms AgS)
– Rusting of iron
(Fe forms Fe2O3)
21. CHEMICAL REACTIONS
Are expressed using chemical equations.
Rusting of iron:
4 Fe + 3 O2 2 Fe2O3 (rust)
reactants products
Meaning:
Four atoms of iron react with three
molecules of oxygen to form two
molecules of rust
22. CHEMICAL REACTIONS (Cont)
Zn + 2 HCl ZnCl2 + H2
Zinc hydrochloric acid zinc chloride hydrogen gas
Meaning:
One atom of zinc reacts with two
molecules of hydrochloric acid to produce
one molecule of zinc chloride and one
molecule of hydrogen gas.
23. CHEMICAL PROPERTIES
Describe ways pure substances behave
when interacting with other pure
substances.
Examples
– Iron reacts with oxygen to form rust.
– Platinum does not react with oxygen at room
temperature.
24. PRACTICE PROBLEM
Identify the following properties and
changes as physical or chemical.
a. The copper sheets that form the “skin” of the
Statue of Liberty have acquired a greenish
coating over the years.
b. Carbon appears as black powder.
c. Adding food coloring to water.
d. Wood burns in air.