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 no definite shape; particles are less tightly packed and can flow past one another.

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

Pure Substances and Mixtures

Pure substances have a fixed composition and distinct properties. They are classified as:

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

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

Mixtures, in contrast, are physical combinations of two or more substances and can be separated by physical means.

Atomic Structure and the Periodic Table

Structure of the Atom

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

• Protons: Positively charged particles located in the nucleus.

• Neutrons: Neutral particles (no charge) also located in the nucleus.

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

The nucleus contains most of the atom's mass, while electrons occupy most of its volume.

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.

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. Example: Sodium chloride (NaCl).

• Covalent Bonds: Formed when two atoms (usually nonmetals) share one or more pairs of electrons. Example: Water (H2O).

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

Significant Figures

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

• When performing calculations, the result should be reported with the correct number of significant figures based on the rules for addition, subtraction, multiplication, and division.

Density

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

• The formula for density is:

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

• Common units: g/cm3 (solids), g/mL (liquids), g/L (gases).

Example: Calculating Density

• If a metal block has a mass of 50.0 g and a volume of 20.0 cm3, its density is: