Matter

Preparation for General Chemistry Prof. Darrin M. York Rutgers, The State University of New Jersey

Matter

• Compare and contrast the common states of matter: solid, liquid, and gas. • Describe the classifications of matter: pure substances (elements and compounds), and mixtures (heterogeneous and homogeneous).

• Describe what constitutes the chemical identity of a pure substance. • State the law of conservation of mass. • Distinguish whether a process corresponds to a chemical or physical change. • Characterize properties as being either chemical or physical in nature, and extensive or intensive.

Chemistry is the study of matter, the changes that matter undergoes and the energy associated with these changes.

Matter is anything that has mass and occupies space.

Atoms are the fundamental building blocks of matter. The word “atom” derives from the Greek word “atomos” which means “indivisible. Matter is composed of atoms that may be connected to one another by chemical bonds. There are different types of chemical bonds, and different ways that chemical bonds give rise to various types of compounds.

Chemical bonds are a form of attraction between atoms that connect them to one another and allow formation of chemical substances There are different types of chemical bonds

• Covalent – involve shared electrons and are directional • Ionic – involve electrostatic force between oppositely charged ions • Metallic – involve delocalized electrons and are non-directional

Covalent Bond Ionic Bond

caffeine, C8H10N4O2

sodium,Na

Metallic Bond

table salt, NaCl

Chemical identity of matter is determined by the atoms from which it is composed, together with the chemical bonds that tie them together, and in some cases geometrical structure. N C O cyanate

diamond C

H

graphite C

Cl

H Cl

cis-dichloroethylene Tb = 48.5 °C

C N O fulminate Cl H

H Cl

trans-dichloroethylene Tb = 60.2 °C

• The law of conservation of mass states that mass is neither created nor destroyed in any chemical or physical process.

• Although matter may be converted from one form into another, the total amount of mass remains constant.

We can classify matter based on: • physical state (solid, liquid or gas) • composition (pure substance or mixture)

Composition

State Solid

Liquid

Gas

Pure Substance Element

Compound

Mixture

Homogeneous Heterogeneous

• Solid: particles are packed close to each other in fixed locations. Solids retain their shape (do not flow), and are fairly incompressible.

• Liquid: particles are packed close to each other but are not in fixed locations. Liquids also are fairly incompressible, but can flow and take the shape of a container (but do not necessarily fill it).

• Gas: particles are generally far away from each other and free to move relative to one another. Gases are easily compressed and fill the volume of their containers.

• A pure substance (or simply a “substance”) is a form of matter that has definite (constant) composition and distinct properties. • A mixture is a physical combination of two or more substances.

Composition Pure Substance Element

Compound

Mixture

Homogeneous Heterogeneous

An element consists of only one type of atom, whereas a compound consists of more than one type of atom.

Pure Substance

Element

Compound

Allotropes

Isomers

Elements can be either:

• atomic (made of individual atoms), e.g. the noble gases

• molecular (made of molecules)

model of atomic element

e.g. O2, O3, Br2, or P4 (white phosphorus)

phosphorus, P4

• covalent or metallic crystal network e.g., diamond (solid C), Ag metal

• Different chemical forms of the same element are called allotropes.

silver,Ag

graphene, C

Compounds are made up of more than one type of atom.

Ethanol, C2H5OH

They can be composed of either molecules (C2H5OH), ions (NaCl), or network solids (SiO2). Isomers are compounds with the same chemical formula, but with different chemical structure.

Sodium Chloride, NaCl

Quartz, SiO2

A homogeneous mixture has components that are uniform throughout.

They are also called solutions. Examples: Salt water, wine, air

A heterogeneous mixture is not uniform throughout, as the components are discernible by the naked eye. Examples: Sand, granite, smog

In physical changes the chemical identity of the substance does not change, only the physical state. Examples: melting, freezing, evaporation, condensation, sublimation, deposition.

In chemical changes the chemical identity of one or more substances changes; e.g., one substance is converted into another. • Examples: oxidation of metals (e.g., rusting or iron, corrosion of copper, tarnishing of silver), combustion, electrolysis of water, neutralization of an acid by a base.

CH4 + 2O2 → CO2 + 2H2O Fe2O3 + 2 Al → 2 Fe + Al2O3

Physical properties can be observed and measured without changing the identity of the substance (i.e., without undergoing a chemical change).

Chemical properties can not be observed without converting the substance into another substance (i.e., without undergoing a chemical change).

Extensive properties

Intensive properties

Depend on the amount of matter.

Do not depend on the amount of matter.

Example: mass, volume, number of particles, energy.

Examples: temperature, density, boiling point, hardness, color, concentration.

• The three common states of matter are solids, liquids and gases, and each has a set of distinct physical properties that allow them to be distinguished.

• Matter can be classified by physical state, or by composition as pure substances or mixtures.

• Chemical identity is determined by the atoms contained in a substance, together with their chemical bonding and geometrical arrangement.

• Mass is neither created nor destroyed in any chemical or physical process.

• Chemical changes result in changes in the chemical identity of one or more substances, whereas physical changes do not.

• Physical properties can be measured without involving a chemical change, whereas chemical properties can not.

• Extensive properties depend on the amount of matter, whereas intensive properties do not.