Classification and Introduction

Chemistry: Introduction: Matter and Measurement Lecture Outline

1.1 The Study of Chemistry

· Chemistry – study of properties of materials and changes that they undergo.

§ Can be applied to all aspects of life (e.g. development of pharmaceuticals, leaf color change in fall).

The Molecular Perspective of Chemistry

Chemistry involves the study of the properties and behavior of matter.

· Matter

§ Physical material of the universe

§ Has mass

§ Occupies space

§ ~100 Elements constitute all matter

§ Elements:

· Made up of unique atoms.

· Names of the elements are derived from a wide variety of sources

(e.g. Latin or Greek, mythological characters, names of people or places).

§ Molecules:

· Combinations of atoms held together in specific shapes.

· Macroscopic (observable) properties of matter relate to microscopic realms of atoms.

· Properties relate to composition (types of atoms present) and structure (arrangement of atoms) present.

Why Study Chemistry?

We study chemistry because:

· It has a considerable impact on society (health care, food, clothing, conservation of natural resources, environmental issues, etc.).

· It is part of your curriculum! Chemistry serves biology, engineering, agriculture, geology, physics, etc. Chemistry is the central science.

1.2 Classifications of Matter

Matter is classified by state (solid, liquid, or gas) or by composition (element, compound, or mixture).

States of Matter

On the macroscopic level:

· Gas No fixed volume or shape, conforms to volume and shape of container, compressible.

· Liquid Volume independent of container, no fixed shape, incompressible.

· Solid Volume and shape independent of container, rigid, incompressible.

On the molecular level

· Gas Molecules far apart, move at high speeds, collide often.

· Liquid Molecules closer than those in gas, move rapidly but can slide over one another.

· Solid Molecules packed closely in definite arrangements.

Pure Substances and Mixtures

· Pure Substance

§ Matter with fixed composition and distinct proportions.

§ Elements (cannot be decomposed into simpler substances, i.e. only one kind of atom) or compounds (consist of two or more elements).

· Mixtures

§ Combination of two or more pure substances.

§ Variable composition.

§ Heterogeneous (do not have uniform composition, properties and appearance, e.g. sand).

§ Homogeneous (uniform throughout, e.g. air). Homogeneous mixtures are solutions.

Separation of Mixtures

Key: Separation techniques exploit differences in properties of the components.

· Filtration: Remove solid from liquid

· Distillation: Boil off one or more components of the mixture

· Chromatography: Exploit solubility of components

Elements

· 112 known

· Vary in abundance

· Each is given a unique name

· Organized in periodic table

· Each given a one- or two-letter symbol derived from its name.

Compounds

· Combination of elements

Example: The compound H₂O is a combination of the elements H and O.

· The opposite of compound formation is decomposition

· Compounds have different properties than their component elements (e.g. water is liquid, hydrogen and oxygen are both gases at the same temperature and pressure).

· Law of constant (definite) proportions (Proust): A compound always consists of the same combination of elements (e.g. water is always 11 percent H and 89 percent O).

Measurement