INTRO CHEMISTRY I CHEM 1405

INTRODUCTION TO CHEMISTRY

Science is organized or systematized knowledge gathered by the scientific method. 

Hypothesis - a guess to try to explain observed events

Theory - the best current explanation of various phenomena

Scientific Laws - theories which have been proven beyond a doubt and no exceptions have been found.  These theories are accepted by the SCIENTIFIC COMMUNITY as fact.

The Scientific Method consists of three steps:

• hypothesis

• set a plan to prove or disprove the hypothesis making sure to control variables

• collect facts and data by observation under controlled conditions (experimentation)

• examine and correlate the data

• compare the analysis of data with the proposed hypothesis (a tentative theory)

• plan and carry out further experimentation to support or refute the hypothesis.

Chemistry is the science concerned with the composition of substances and the changes they undergo.

Chemistry has five major subfields:

• organic
• inorganic
• analytical
• physical
• biochemistry

Chemistry is considered the Central Science.

MATTER AND MASS  

Matter - anything that has mass and occupies space.
Mass - the quantity of matter in a particular body.
Weight - affected by gravity and may vary, mass is not affected by gravity

Properties of Pure Substances

Physical properties can be observed without changing the composition of the substance.

Types of physical properties are:

• color
• odor
• taste
• solubility
• density
• melting point
• boiling point

Chemical properties can be observed when a substance undergoes a change in composition.

Types of chemical properties:

• iron rusting
• gasoline burning in air
• water undergoing electrolysis
• chlorine reacts with sodium

Changes of Pure Substances

Physical changes occur without a change in the composition of the substance. Conversions from one state of matter to another is an example of a physical change.

• melting
• freezing
• boiling

Chemical changes are observed when a change in the composition of a substance occurs. New substances are formed with different physical and chemical properties.

Cl₂ + Na ---> 2 NaCl

chlorine gas (poisonous) plus sodium (reactive metal) produces a new substance, sodium chloride (table salt) which has totally different physical and chemical properties.

• explodes
• burns
• rusts

Physical States of Matter

Matter exists in three physical states:

• Solid
• Liquid
• Gas

Composition and Properties of Matter

Composition - the types of atoms that are present and their relative proportions and structures in relation to each other.

Homogeneous matter is uniform in:

• composition
• properties

Heterogeneous matter is not uniform in:

• composition
• properties

Heterogeneous matter consists of two or more substances unequally distributed and is often referred to as a mixture.

Heterogeneous matter is composed of two or more pure substances which can be separated.

Solutions are homogeneous mixtures composed of two or more pure substances.

Pure substances are characterized by definite and constant:

• Composition
• Properties

Compounds and Elements

Pure substances are divided into two groups:  

• Compounds - pure substances which can be broken down by chemical means to two or more simpler substances elements and are composed of molecules. Compounds are represented by molecules which is the smallest particle of an compound.

• Molecules are groups of two or more atoms.

• Elements - pure substance which cannot be decomposed into simpler substances by ordinary chemical means and are composed of atoms.  Elements are represented by atoms which is the smallest particle of an element.

Common elements and symbols

SCIENTIFIC NOTATION

Scientific notation is a method that allows one to write very large or small numbers in shorthand. 

For example, the number 27000000000000 can be written in scientific notation as 2.7 x 10¹³ or the number 0.00000073 can be written as 7.3 x 10^{- 7}.

 To do this,  write the number as a factor between 1 and 10 multiplied by 10 raised to a power.

 Procedure:

• Move the decimal point in the original number so that it is located after the first non-zero digit.

 Example:      2468   ------->   2.468

• Multiply this new number by 10 raised to the proper power.  The power of 10 is equal             to the number of places that the decimal point was moved.

         Example:      2468   ------->   2.469 x 10^?    ------->  2.469 x 10³

The decimal point was moved three places.
Therefore the power of ten is 3.

• Determine if the power of 10 is positive or negative.

If the decimal point was moved to the left, the exponent is positive. 

Example: 2468 = 2.468 x 10 ³

 If the initial number is larger than 1, the power of 10 will be positive.

 If the decimal point was moved to the right, the exponent is negative.

 Example: 0.000123 = 1.23 x 10 ^{- 4}

If the initial number is less than 1, the power of 10 will be negative.

MEASURING MATTER: The Metric System     (right click to download metric system tutorial program)
 

The metric system was developed in 19th century France. The United States is one of the few countries not using the metric system.

The metric system has three basic units for measuring matter:

• gram  (mass)
• liter (volume)
• meter (distance)

The units are expressed in multiples of 10.

The metric system uses prefixes to define multiples or fractures of the basic units.

Conversion of metric to metric

Metric conversions uses dimensional analysis (factoring) to convert one metric prefix to another.   The conversions is accomplished by conversion factors:

Example: Convert 4 grams to mg.

 

Example: Convert 80 ml to kl.

You have two sets of conversion factors.

or

or

Since we do not know how to convert directly from ml to kl, we first convert ml to liters then liters to kiloliters.

Example: Convert 5 cm to um

You have two sets of conversion factors:

You have two sets of conversion factors:

or

or

Since we do not know how to directly convert from cm to um, we first convert to liters than to um.

Metric - English Conversions

Sometimes it is necessary to convert from the english system to the metric system or vice versa.

To do this we need three conversion factors.

1 in  = 2.54 cm

1 lb  = 454 g

1 qt  = 946 ml

Example: Convert 24 oz. to kg

Example: Convert 8 meters to yards.

DENSITY                                        (right click to download density tutorial program)
 

Density is mass per unit volume.


In science we normally use g/ml (g/ml³) for solids and liquids and g/l for gases.

Example: A cube of iron measures 2 cm x 2 cm x 3 cm and has a mass of 80g. Calculate the density.

Volume = 3 cm x 2 cm x 2 cm = 12 cm³

mass = 80g

Energy

Energy is defined as the ability to do work or to transfer heat.

The principle types of energy are:

• mechanical
• heat
• electrical
• chemical
• light

Energy can either be

• potential energy - energy possessed by its position in space or its chemical composition or
• kinetic energy - due to motion

Heat energy - energy is transferred from one substance to another when there is a temperature difference between the substances.

Measurement of Energy (units)

• Calorie (cal)
• Joule (j)
• 1 cal = 4.184 j

A calorie is  the quantity of heat required to raise the temperature of 1 gram of water from 14.5 ^oC to 15.5 ^oC.

TEMPERATURE CONVERSIONS                 (right click to download temperature tutorial program)
 

There are three commonly used temperature systems:

• Fahrenheit
• Celsius (Centigrade)
• Kelvin

We commonly have to convert from one system to another.

Celsius to Fahrenheit

Fahrenheit to Celsius

Celsius to Kelvin

Fahrenheit to Kelvin

Convert from ^oF to ^oC then to Kelvin

Kelvin to Fahrenheit

Convert from K to ^oC then to ^oF