Chapter # 4

Basic Concepts of Matter

Matter DefinedMatter Defined

• Matter can be invisible.– Air is matter, but it cannot be seen.

• Matter appears to be continuous and unbroken.

– Matter is actually discontinuous. It is made up of tiny particles call atoms.

• Matter is anything that has mass and occupies space.

Physical States of Physical States of MatterMatter

Shape • Definite - does not change. It is independent of its container.

Volume • Definite

Particles • Particles are close together. Theycohere rigidly to each other.

SOLIDS

Compressibility • Very slight–less than liquidsand gases.

Solid

Amorphous Solid Crystalline Solid

Particles lack a regularinternal arrangement

Particles exist in regular, repeating three-dimensional geometric patterns.

Glass, plastics, gels Diamond, metals, salts

A solid can be either crystalline or amorphous. Which one it is depends on the internal arrangement of the particles that constitute the solid.

Shape • Not definite - assumes the shape of its container.

Volume • Definite

Particles • Particles are close together.• Particles are held together by

strong attractive forces.• They can move freely throughout

the volume of the liquid.

LIQUIDS

Compressibility • Very slight–greater than solids,less than gases.

GASES

Shape • No fixed shape.

Volume • Indefinite.

Particles • Particles are far apart compared to liquids and solids.

• Particles move independently of each other.

GASES

Compressibility • The actual volume of the gas particles is small compared to the volume of space occupied by the gas.– Because of this a gas can be

compressed into a very small volume or expanded almost indefinitely.

• Attractive forces are strongest in a solid.– These give a solid rigidity.

ATTRACTIVE FORCES

Solid

Liquid • Attractive forces are weaker in liquids than in solids.– They are sufficiently strong so that a

liquid has a definite volume.

ATTRACTIVE FORCES

Gas • Attractive forces in a gas are extremely weak.

• Particles in the gaseous state have enough energy to overcome the weak attractive forces that hold them together in liquids or solids.– Because of this the gas particles move

almost independently of each other.

Properties of Matter

• A property is a characteristic of a substance.

• Each substance has a set of properties that are characteristic of that substance and give it a unique identity.

Properties of a Substance

Physical PropertiesPhysical Properties

• The inherent characteristics of a substance that are determined without changing its composition.

• Examples:

taste color physical state melting point boiling point

Chemical PropertiesChemical Properties

Describe the ability of a substance to form new substances, either by reaction with other substances or by decomposition.

tearing of paper change of ice into water change of water into steam heating platinum wire

• Changes in physical properties (such as size shape and density) or changes in the state of matter without an accompanying change in composition.

• Examples:

Physical Changes

• No new substances are formed.

Chemical ChangesChemical ChangesChemical ChangesChemical Changes

In a chemical change new substances are formed that have different properties and composition from the original material.

Water is decomposed into hydrogen and oxygen by passing electricity through it.

Decomposition of Water

The composition and physical appearance of hydrogen and oxygen are different from water.The hydrogen explodes with a pop upon the addition of a burning splint.The oxygen causes the flame of a burning splint to intensify.

They are both colorless gases.But the burning splint is extinguished when placed into the water sample.

Chemical EquationsChemical Equations

Water decomposes into hydrogen and oxygen when electrolyzed.

reactant productsyields

Chemical symbols can be used to express chemical reactions

Substance

A particular kind of matter that has a fixed composition and distinct properties.

Examples

ammonia, water, and oxygen.

Homogeneous Matter

Matter that is uniform in appearance and with uniform properties throughout.

Examples

ice, soda, pure gold

Heterogeneous Matter

Matter with two or more physically distinct phases present.

Examples

ice and water, wood, blood

Homogeneous

Heterogeneous

Phase

A homogenous part of a system separated from other parts by physical boundaries.

Examples

In an ice water mixture ice is the solid phase and water is the liquid phase.

Mixture

Matter containing 2 or more substances that are present in variable amounts. Mixtures are variable in composition. They can be homogeneous or heterogeneous.

Homogeneous Mixture (Solution)

A homogeneous mixture of 2 or more substances. It has one phase.

ExampleSugar and water. Before the sugar and water are mixed each is a separate phase. After mixing the sugar is evenly dispersed throughout the volume of the water.

Example

Sugar and fine white sand. The amount of sugar relative to sand can be varied. The sugar and sand each retain their own properties.

Heterogeneous MixtureA heterogeneous mixture consists of 2 or more phases.

Example• Iron (II) sulfide (FeS) is 63.5% Fe and 36.5% S

by mass.

• Mixing iron and sulfur in these proportions does not form iron (II) sulfide. Two phases are present: a sulfur phase and an iron phase.

• If the mixture is heated strongly a chemical reaction occurs and iron (II) sulfide is formed.

• FeS is a compound of iron and sulfur and has none of the properties of iron or sulfur.

Heterogeneous MixtureA heterogeneous mixture consists of 2 or more phases.

Heterogeneous Mixture of One Substance

A pure substance can exist as different phases in a heterogeneous system.

Example

Ice floating in water consists of two phases and one substance. Ice is one phase, and water is the other phase. The substance in both cases is the same.

SystemThe body of matter under consideration.

Examples

In an ice water mixture ice is the solid phase and water is the liquid phase. The system is the ice and water together.

ElementsElements

An element is a fundamental or elementary substance that cannot be broken down into simpler substances by chemical means.

• All known substances on Earth and probably the universe are formed by combinations of more than 100 elements.

• Each element has a number.– Beginning with hydrogen, as 1 the

elements are numbered in order of increasing complexity.

• Most substances can be decomposed into two or more simpler substances.

– Water can be decomposed into hydrogen and oxygen.

– Table salt can be decomposed into sodium and chlorine.

• An element cannot be decomposed into a simpler substance.

Symbols of the Symbols of the ElementsElements

• A symbol stands for

– the element itself

– one atom of the element

– a particular quantity of the element

Ne neon

Rules governing symbols of the elements are:

1. Symbols have either one or two letters.

2. If one letter is used it is capitalized.

3. If two letters are used, only the first is capitalized.

H hydrogenC carbon

Ba barium

Most symbols start with the same letter as the element.A number of symbols appear to have no connection with the element.These symbols have carried over from the earlier names of the elements (usually Latin).