Chapter 1 Introduction to Chemistry. Section 2 Objectives w Define chemistry & matter w Compare & contrast mass & weight w Explain why chemists are interested.

Chapter 1

Introduction to Chemistry

Section 2 Objectives

Define chemistry & matter Compare & contrast mass & weight Explain why chemists are interested in a

submicroscopic description of matter

Definitions

Chemistry is the study of matter & the changes that it undergoes.• Matter is anything that has mass & volume.• Mass is a measurement that indicates the

amount of matter.• Volume is a measurement that indicates how

much space something takes up.

Matter Is air matter?

Matter

What is NOT matter?

Mass and Weight Weight is a measure not only of the amount

of matter (that is, the mass) but also of the effect of Earth’s gravitational pull on that matter.

A scale measures the

downward force of

gravity on an object.

Mass and Weight Since the force of gravity is

not the same everywhere, the weight of an object is not a constant.

Mass is used in science because it is independent of gravitational force.

Your MASS will never change but your WEIGHT will, depending on where you are!

Size of Matter Some matter is macroscopic - it is able to

be seen without the use of a microscope. A tremendous variety of matter, however,

is submicroscopic. This matter is too small even to be seen with an optical microscope.

All matter is composed of elements. Elements are made up of atoms. Atoms are submicroscopic.

Submicroscopic Matter The structure, composition, & behavior of

all matter depends on atoms and the changes they undergo.

Chemists use models (visual, verbal, or mathematical representations) to explain atoms and chemical changes.

Section 3 Objectives

Identify the common steps of the scientific method.

Compare & contrast types of data. Compare & contrast types of variables. Describe the difference between a theory &

a law.

The Scientific Method The systematic approach used in scientific

study is called the scientific method. If all scientists use common procedures as

they conduct their experiments, they are able to verify the work of one another.

The steps listed on the following slides will be those we will use in our laboratory activities & reports this year.

The Scientific Method

1 - Ask a QUESTION.

Based on existing knowledge & the observation of natural occurrences, a scientist will ask a question whose answer can be tested through experimentation.


2 - Form a HYPOTHESIS.

A scientist will form a tentative answer for the question that she asked. The scientist will then collect data to support or refute this “educated guess”.


3 - Conduct an EXPERIMENT.

An experiment is a set of controlled observations that test a hypothesis. It must be “reproducible” - that is, the experiment must be designed so that anyone can use the same materials and follow the same procedure.

The Scientific Method3 - Conduct an EXPERIMENT(cont.)

An experiment must test one variable at a time. A variable is a quantity or condition that can have more than one value.

For example, suppose you want to test the hypothesis that table salt will dissolve faster in water that is 40 0C than in water that is 20 0C.


Since you will be changing or manipulating the temperature, it is considered the manipulated or independent variable. The rate or time of dissolving will then respond to or depend upon the temperature. It is called the responding or dependent variable.


Since an experiment can only test one variable at a time, other conditions (like the amount of water or salt used) must be constant at each temperature tested. Constant factors cannot be allowed to change during the experiment.


3 - Conduct an EXPERIMENT(cont.)

Experiments usually have a control or standard for comparison. In this case, the rate of dissolving at 40 0C is compared to the rate of dissolving at 20 0C. Therefore, the time it takes to dissolve the salt at

20 0C is the control.

The Scientific Method4 - Make OBSERVATIONS & collect

DATA An observation is the act of gathering

information. Data is the information gathered.

The Scientific Method4 - Make OBSERVATIONS & collect DATA

There are 2 types of observations/data.

1. qualitative This type uses words to describe a physical

characteristic - how something looks, feels, smells, sounds, or tastes.

2. quantitative This type uses numbers - it tells you how

much, how big, or how fast, for example.

The Scientific Method4 - Make OBSERVATIONS & collect DATA

The Scientific Method5 - ANALYZE the data & draw CONCLUSIONS.

Data analysis may involve performing calculations with the data or graphing the data. In any case, scientists analyze the data for any patterns that may exist.


5 - ANALYZE the data & draw CONCLUSIONS

(cont).

A conclusion is a judgement based on the data obtained. It will support or refute a hypothesis.

Using Data

Models can be created to explain data. They can then be tested and used to make predications.

A theory can be formed. A theory is an explanation for the data. It must be supported by many, many experiments and is modified when new data is obtained.

Using Data

Scientific law is developed to summarize the results of natural occurrences. These are formed only when many experiments have taken place and no exceptions have ever occurred.

Theory vs. Law

The kinetic-molecular theory explains why gases behave the way they do. Theories explain.

The gas laws summarize all the ways that gases behave in different situations. Laws summarize.

Chapter 1 Introduction to Chemistry. Section 2 Objectives w Define chemistry & matter w Compare & contrast mass & weight w Explain why chemists are interested.

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