Matter and Its Classification

Definition of Matter

Matter is defined as anything that has mass and occupies space. All physical substances, regardless of their state or composition, are considered matter in chemistry.

• States of Matter: The three primary states are solid, liquid, and gas.

• Solids: Have a definite shape and volume.

• Liquids: Have a definite volume but take the shape of their container.

• Gases: Have neither definite shape nor volume; they expand to fill their container.

Classification of Substances

• Pure Substance: A material with a fixed composition and distinct properties. Examples include elements and compounds.

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

• Compound: A pure 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, while iron (Fe) is an element.

Atomic Structure and the Periodic Table

Structure of the Atom

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

• Protons: Positively charged particles located in the nucleus.

• Neutrons: Neutral particles (no charge) also found 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.

Example: Hydrogen (H) has atomic number 1; Carbon (C) has atomic number 6.

Chemical Bonds

Ionic and Covalent Bonds

Chemical bonds are forces that hold atoms together in compounds.

• Ionic Bonds: Formed when electrons are transferred from one atom (usually a metal) to another (usually 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) forms via ionic bonding; water (H2O) forms via covalent bonding.

Measurement in Chemistry

SI Units

The International System of Units (SI) is the standard for scientific measurements.

• Meter (m): Unit of length

• Kilogram (kg): Unit of mass

• Second (s): Unit of time

• Kelvin (K): Unit of temperature

• Mole (mol): Unit for amount of substance

Significant Figures

Significant figures indicate the precision of a measured quantity. The number of significant figures in a value reflects the certainty of the measurement.

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant; trailing zeros are significant only if there is a decimal point.

Example: 0.00450 has three significant figures.

Density

Density is a physical property defined as the mass of a substance per unit volume.

• Formula:

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

Example: If a sample has a mass of 10.0 g and a volume of 2.0 mL, its density is .