TEMA PARA LA MATERIA DE QUÍMICA...t/t

1. WHAT IS CHEMISTRY?
QBA Miguel A. Castro Ramírez

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.

9. CLASSIFICATION OF MATTER

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

13. COMPOUNDS (cont)
 Are H2
and O3 considered elements or
compounds? Why?

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

15. STATES OF MATTER
Solid Liquid Gas
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings

16. WATER AND ITS STATES OF
MATTER

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.