Unit 1

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Properties of Matter

Physical: based on appearance color, size, state

Chemical: ability to undergo chem. change Ex: flammability and explosions

How can we characterize and detect these changes?

A phys. change is generally associated with

Phase size texture

These changes are reversible

A chem. chance is generally associated with a color change the evolution of a gas or the formation of a precipitate

In each of these changes a new substance is formed

changes are irreversible ex: burning paper

We can classify matter as:

Pure substance: definite properties and compact composition

Ex: Oxygen

Element: one kind of atom

Compound: more than one element

Mixture: composed of more than one substance consequence: varying properties

Air, tap water, milk, blue cheese, bread,

and dirt are all mixtures

Homogenous mixtures a.k.a. solutions: uniform and consists of one phase air and tap water

Homogeneous mixtures (solutions) can be separated into their component substances by physical processes that rely

on differences in some physical property

Distillation makes use of differences in volatility, a measure of how easily a

substance is converted to a gas at a given temperature

The most volatile component boils first and is condensed back to a liquid in the water-cooled condenser, from which

it flows into the receiving flask. If a solution of salt and water is distilled, for example, the more volatile component,

pure water, collects in the receiving flask, while the salt remains in the distillation flask

Crystallization separates mixtures based on differences in solubility, a measure of how much solid substance

remains dissolved in a given amount of a specified liquid

the liquid, called the solvent, may be allowed to evaporate. In either case, the least soluble of the

dissolved substances, the one that is least likely to remain in solution, usually forms crystals first, and these crystals

can be removed from the remaining solution by filtration

The chemical composition of a substance is altered in a process called

achemical change. The conversion of two or more elements, such as sodium and chlorine, to a chemical compound,

sodium chloride, is an example of a chemical change, often called a chemical reaction

a reverse chemical process breaks down compounds into their elements. For example, water (a compound)

can be decomposed into hydrogen and oxygen (both elements) by a process called electrolysis. In electrolysis,

electricity provides the energy needed to separate a compound into its constituent elements

Solid solutions

of two or more metals are commonly called alloys.

Heterogeneous: not uniform and consists of more than one phase

Solid-liquid mixtures such as sand

in water or tea leaves in tea are readily separated by filtration

Physical Properties

Extensive: depends on the amt. or magnitude ex: volume, mass, and weight

Intensive: independent of the amount ex: physical state at a given temperature, color, melting point, boiling point, electrical conductivity or density

Scientists commonly

measure intensive properties to determine a substance’s identity, whereas extensive properties convey

information about the amount of the substance in a sample

For example, elemental sulfur is a yellow crystalline solid that does

not conduct electricity and has a melting point of 115.2°C, no matter what amount is examined

Chemical Properties

Although mass and volume are both extensive properties, their ratio is an important intensive property

called density (d). Density is defined as mass per unit volume and is usually expressed in grams per cubic \22

centimeter (g/cm3). As mass increases in a given volume, density also increases.

EQUATIONS!

density = mass volume > d=mv

Table 1.1 Densities of Common Substances

Substance Density at 25°C (g/cm3)

Pure water, for example, has a density of 0.998 g/cm3 at 25°C

blood 1.035

body fat 0.918

whole milk 1.030

corn oil 0.922

mayonnaise 0.910

honey 1.420

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History of Chemistry

It was not until the era of the ancient Greeks that we have any record of how people tried to explain the chemical

changes they observed and used

Then, in the fourth century BC, two Greek philosophers, Democritus and Leucippus,

suggested that matter was not infinitely divisible into smaller particles but instead consisted of fundamental,

indivisible particles called atoms.

They would have been unlikely to do so in any case because the ancient Greeks did not conduct

experiments or use the scientific method. They believed that the nature of the universe could be discovered by

rational thought alone.

Over the next two millennia, alchemists, who engaged in a form of chemistry and speculative philosophy during the

Middle Ages and Renaissance, achieved many advances in chemistry. Their major goal was to convert certain

elements into others by a process they called transmutation

Modern Chemistry

The 16th and 17th centuries saw the beginnings of what we now recognize as modern chemistry. During

this period, great advances were made in metallurgy, the extraction of metals from ores

In 1661, the Englishman Robert Boyle (1627–91)

published The Sceptical Chymist, which described the relationship between the pressure and the volume

of air. More important, Boyle defined an element as a substance that cannot be broken down into two or

more simpler substances by chemical means.

In the 18th century, the English clergyman Joseph Priestley (1733–1804) discovered oxygen gas and

found that many carbon-containing materials burn vigorously in an oxygen atmosphere, a process

called combustion. Priestley also discovered that the gas produced by fermenting beer, which we nowknow to be carbon dioxide, is the same as one of the gaseous products of combustion.

showed that

combustion is the reaction of a carbon-containing substance with oxygen to form carbon dioxide and

water and that life depends on a similar reaction, which today we call respiration. Lavoisier also wrote the

first modern chemistry text and is widely regarded as the father of modern chemistry. His most important

contribution was the law of conservation of mass, which states that in any chemical reaction, the mass of the substances that react equals the mass of the products that are formed. That is, in a chemical reaction,

mass is neither lost nor destroyed.

In 1803, the English schoolteacher John Dalton (1766–1844)

Dalton’s atomic theory of

matter contains four fundamental hypotheses:

All matter is composed of tiny indivisible particles called atoms.

All atoms of an element are identical in mass and chemical properties, whereas atoms of

different elements differ in mass and fundamental chemical properties.

3. A chemical compound is a substance that always contains the same atoms in the same

ratio.

4. In chemical reactions, atoms from one or more compounds or elements redistribute or

rearrange in relation to other atoms to form one or more new compounds.Atoms

themselves do not undergo a change of identity in chemical reactions.

with four minor modifications:

Not all atoms of an element must have precisely the same mass.

Atoms of one element can be transformed into another through nuclear reactions.

The compositions of many solid compounds are somewhat variable.

Under certain circumstances, some atoms can be divided (split into smaller particles).

law of multiple proportions: when two elements

form a series of compounds, the ratios of the masses of the second element that are present per gram of the first element can almost always be expressed as the ratios of integers

Gay-Lussac

found, for example, that one volume of chlorine gas always reacted with one volume of hydrogen gas to

produce two volumes of hydrogen chloride gas. Similarly, one volume of oxygen gas always reacted with

two volumes of hydrogen gas to produce two volumes of water vapor the first element can almost always be expressed as the ratios of integers

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