Chapter 4 Basic Concepts of Matter Matter Defined

Chapter # 4 Basic Concepts of Matter

Matter Defined

• Matter is anything that has mass and occupies space. • 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.

Physical States of Matter

SOLIDS Shape • Definite - does not change. It is independent of its container. Volume • Definite Particles • Particles are close together. They cohere rigidly to each other. Compressibility • Very slight–less than liquids and gases.

A solid can be either crystalline or amorphous. Which one it is depends on the internal arrangement of the particles that constitute the solid. Solid Amorphous Solid Crystalline Solid Particles lack a regular internal arrangement Particles exist in regular, repeating three-dimensional geometric patterns. Glass, plastics, gels Diamond, metals, salts

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

Properties of a Substance • 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.

Physical Properties

• The inherent characteristics of a substance that are determined without changing its composition. • Examples: § taste § color § physical state § melting point § boiling point

Chemical Properties

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

Physical Changes • Changes in physical properties (such as size shape and density) or changes in the state of matter without an accompanying change in composition. • Examples: § tearing of paper § change of ice into water § change of water into steam § heating platinum wire • No new substances are formed.

Chemical Changes

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

Decomposition of Water The composition hydrogen explodes and physical with a appearance pop upon of Water They But the are is decomposed burning both colorless splint into gases. is hydrogen extinguished and the when hydrogen addition ofand athe burning oxygen splint. are different from oxygeninto placed by passing water electricity sample. through it. water. The oxygen causes the flame of a burning splint to intensify.

Chemical Equations

Water decomposes into hydrogen and oxygen when electrolyzed. reactant yields products

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 that is uniform in appearance and with uniform properties throughout. Examples ice, soda, pure gold

Heterogeneous 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. Example Sugar 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.

Heterogeneous Mixture A heterogeneous mixture consists of 2 or more phases. 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 Mixture A heterogeneous mixture consists of 2 or more phases. Example • Iron (II) sulfide (Fe. S) 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. • Fe. S is a compound of iron and sulfur and has none of the properties of iron or sulfur.

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.

System The 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.

Elements

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 Elements

• A symbol stands for – the element itself – one atom of the element – a particular quantity of the element

Rules governing symbols of the elements are: 1. Symbols have either one or two letters. 2. If one letter is used it is capitalized. H carbon C hydrogen 3. If two letters are used, only Ba Ne barium neon the first is capitalized.

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