Chemistry: An Introduction

A Story of Two Chemicals• The ozone layer in the earth’s atmosphere protects us from the damaging effects of

ultraviolet (UV) radiation, which allows for life on earth.• Ozone: a substance consisting of three parts (atoms) of oxygen (O3). Ozone is formed

when oxygen gas (O2) is exposed to UV rays, which breaks apart the oxygen gas. Some of these oxygen particles interact with oxygen gas to form ozone (O3).

• We live in the earth’s trophosphere, which is located from the earth’s surface, up to where planes fly & weather occurs.

• The next layer out is the stratosphere. This is where Ozone is located, spread out in a layer.

• Function of the ozone layer: absorption of UV radiation, and formation of oxygen gas.• The ozone layer was measured in the 1920’s to be 300 “Dobson” units. It was re-

measured in in the 1970’s & found to be at 160 Dobson units……. Obviously thinning!• In 1928, refrigerators air conditioners, plastic foams & spray cans used

chlorofluorocarbons (CFC’s) as a coolant and propellant. CFC’s contain chlorine, fluorine & carbon.

• This lead to a ban on the use of CFC’s in many countries around the world, but the damage was already done!

• This is only one of many, many reasons WHY it is so important to study chemistry!• Chemistry touches every area of our lives, and is the basis of all science!

What is chemistry?

• Chemistry= The study of matter, and the changes it undergoes.– It is central to all sciences!

• Matter= anything that has mass and takes up space.• Mass= a measurement that reflects the amount of matter in an

object.– Books, pens, etc take up space, and have mass.– Air…… also takes up space (like in a balloon!) and has mass.– The only things in our world that are not matter and have no

mass is:• Heat• Light• Radio waves• Magnetic fields

• Mass vs weight– Weight= the amount of matter, and the effect of the

earth’s gravitational pull on that matter.• weight will decrease as you move away from the earth’s surface• we weigh more on earth than we would on the moon, because

there is more gravity on the earth.• “mass” is used to measure, because it is independent of

gravitational pull.

• Most matter and its behavior is macroscopic (don’t need a microscope to see it)– All matter is made from elements, which are comprised

of smaller particles called atoms.– To understand the macroscopic world, we must first

understand the sub-microscopic level.• Chemistry seeks to do this very thing!

• organic chemistry: the study of carbon-containing compounds.

• Inorganic chemistry: the study of mostly non-carbon containing compounds.

• Physical chemistry: the behavior and changes of matter, and the related energy changes

• Analytical chemistry: components and composition of substances.

• Biochemistry: matter and processes of living organisms.

5 Branches of Chemistry

Scientific Method• Scientists need to use common procedures in order to

combine their work and insights.• This common procedure is called “The Scientific Method”• Scientific method: A systematic approach used in

scientific study.• It is an organized process for performing research• It provides a method that can be followed for scientists to

verify the work of others.• The typical steps of the scientific method are:

• Observation• Hypothesis• Experiments• Draw Conclusions

Scientific Method Steps

1. Observation: the “act” of gathering information (data that is witnessed).• Qualitative data: info that describes color, odor, shape &

other physical characteristics• Quantitative data: info that is measured numerically (always

has a number!).

2. Hypothesis: a possible/tentative explanation for what has been observed.• It is a testable statement• Experiments would need to be done to prove the validity of

the hypothesis

1. Perform experiments: a set of controlled observations that test the hypothesis• Provides data to help decide whether or not to support

the hypothesis.• Uses variables: a quantity or condition that can have

more than one value – There are both independent & dependent variables– Independent Variable: the variable that the

experimenter plans to change (manipulate) to monitor its effect on the experiment. *** should be only one within the experiment.

– Dependent Variable: the variable whose value depends on the independent variable; it will change when the independent variable is manipulated.

– Conclusion: a judgment based on the info obtained.• Does it support the hypothesis? (**A Hypothesis can

never be proven!)• If judgment supports hypothesis, it is given a “thumbs

up”• If not, must be discarded/modify the hypothesis

Additional Scientific Method Terms

• Model: a visual, verbal, and/or mathematical explanation of experimental data. (can be tested & used to make predictions)

• Theory: An interpretation/explanation of why something in nature behaves a particular way. These explanations have been supported by many experiments. Theories are subject to new data & can be modified.

• Constant: A factor in an experiment which is not allowed to change during the experiment.

• Control: A standard for comparison. (some experiments have them)

• Scientific/Natural Law: A summary of observed/measurable behavior. No exceptions are found in nature (always happens). Doesn’t explain why it happens, only that it always happens.