Matter and Its Classification

Definition and States of Matter

Matter is defined as anything that has mass and occupies space. It exists in three primary physical states, each with distinct properties:

• Solid: Definite shape and volume; particles are closely packed and vibrate in place.

• Liquid: Definite volume but takes the shape of its container; particles are less tightly packed and can move past one another.

• Gas: No definite shape or volume; particles are far apart and move freely.

Example: Ice (solid), water (liquid), and steam (gas) are all forms of H2O in different states.

Pure Substances and Mixtures

Pure substances have a fixed composition and distinct properties. They are classified as either elements or compounds:

• Element: A substance that cannot be broken down into simpler substances by chemical means. Examples: Oxygen (O2), Gold (Au).

• Compound: A substance composed of two or more elements chemically combined in fixed proportions. Examples: Water (H2O), Carbon dioxide (CO2).

Example: Table salt (NaCl) is a compound; iron (Fe) is an element.

Atomic Structure and the Periodic Table

Structure of the Atom

Atoms are the basic units of matter, composed of three fundamental particles:

• Protons: Positively charged particles located in the nucleus.

• Neutrons: Neutral particles also found in the nucleus.

• Electrons: Negatively charged particles that orbit the nucleus in electron clouds or shells.

Example: A carbon atom has 6 protons, 6 neutrons, and 6 electrons.

The Periodic Table

The periodic table organizes elements by increasing atomic number (number of protons). Elements in the same column (group) have similar chemical properties.

• Rows: Called periods; indicate energy levels.

• Columns: Called groups or families; elements share similar valence electron configurations.

Example: Group 1 elements (alkali metals) are highly reactive metals.

Chemical Bonds

Ionic and Covalent Bonds

Chemical bonds are forces that hold atoms together in compounds. The two main types are:

• Ionic Bonds: Formed when electrons are transferred from a metal to a nonmetal, resulting in oppositely charged ions that attract each other.

• Covalent Bonds: Formed when two atoms (usually nonmetals) share one or more pairs of electrons.

Example: Sodium chloride (NaCl) is an ionic compound; water (H2O) is a covalent compound.

Measurement in Chemistry

SI Units

The International System of Units (SI) is the standard for scientific measurements. Key SI base units include:

• Meter (m): Length

• Kilogram (kg): Mass

• Second (s): Time

• Kelvin (K): Temperature

• Mole (mol): Amount of substance

Example: The mass of a sample may be measured in kilograms (kg).

Significant Figures

Significant figures (sig figs) indicate the precision of a measured quantity. The number of significant figures in a measurement includes all certain digits plus one uncertain digit.

• Rules for determining significant figures depend on the presence of zeros and decimal points.

• When performing calculations, the result should be reported with the correct number of significant figures.

Example: 0.00450 has three significant figures.

Density

Density is a physical property defined as mass per unit volume. It is useful for identifying substances and for calculations involving mass and volume.

• Formula:

• Where d is density, m is mass, and V is volume.

Example: If a block has a mass of 10 g and a volume of 2 cm3, its density is .