Matter and Its Classification

Definition of Matter

Matter is defined as anything that has mass and occupies space. All physical substances in the universe are forms of matter.

• States of Matter: Matter exists in three primary states: 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.

• Element: A pure substance that cannot be broken down into simpler substances by chemical means (e.g., hydrogen, oxygen).

• Compound: A pure substance composed of two or more elements chemically combined in fixed proportions (e.g., water (H2O), carbon dioxide (CO2)).

Example: Water is a compound made from hydrogen and oxygen; it can be decomposed into these elements by chemical means.

Atomic Structure and the Periodic Table

Atoms and Subatomic Particles

Atoms are the basic units of matter, consisting of three main subatomic 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 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 with similar chemical properties are grouped in columns called groups or families.

• Rows: Called periods.

• Columns: Called groups or families.

Chemical Bonds

Ionic Bonds

Ionic bonds form when electrons are transferred from one atom to another, typically between a metal and a nonmetal. This transfer creates positively charged ions (cations) and negatively charged ions (anions), which are held together by electrostatic attraction.

• Example: Sodium chloride (NaCl) forms when sodium (a metal) transfers an electron to chlorine (a nonmetal).

Covalent Bonds

Covalent bonds form when two atoms share one or more pairs of electrons. This type of bonding typically occurs between nonmetal atoms.

• Example: In a water molecule (H2O), each hydrogen atom shares an electron with the oxygen atom.

Measurements in Chemistry

SI Units

The International System of Units (SI) is the standard for scientific measurements. The main SI units used in chemistry are:

• Meter (m): Unit of length

• Kilogram (kg): Unit of mass

• Second (s): Unit of time

• Kelvin (K): Unit of temperature

• Mole (mol): Unit for the 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 the first uncertain digit.

• Example: The measurement 4.56 g has three significant figures.

Density

Density is a physical property defined as the mass of a substance divided by its 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 .