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 states: solid, liquid, and gas.

• Solid: Has a definite shape and volume; particles are closely packed and vibrate in place.

• Liquid: Has a definite volume but takes the shape of its container; particles are less tightly packed and can move past each other.

• Gas: Has neither definite shape nor volume; particles are far apart and move freely.

Classification of Matter

Matter can be classified as pure substances or mixtures. Pure substances have a fixed composition and can be further divided into elements and compounds.

• Element: A substance that cannot be broken down by chemical means. Examples: Hydrogen (H), Oxygen (O).

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

Example: Water is a compound because it consists of hydrogen and oxygen atoms chemically bonded.

Atomic Structure and the Periodic Table

Atoms and Subatomic Particles

Atoms are the basic units of matter and consist of three main subatomic particles:

• Proton: Positively charged particle located in the nucleus.

• Neutron: Neutral particle located in the nucleus.

• Electron: Negatively charged particle that orbits the nucleus.

Example: The hydrogen atom contains one proton and one electron, but no neutrons.

The Periodic Table

The periodic table organizes elements by their atomic number, which is the number of protons in the nucleus.

• Atomic Number: Determines the identity of an element.

• Organization: Elements are arranged in rows (periods) and columns (groups) based on similar properties.

Chemical Bonds

Ionic and Covalent Bonds

Chemical bonds are forces that hold atoms together in compounds. The two main types are ionic and covalent bonds.

• Ionic Bond: Formed when electrons are transferred from a metal to a nonmetal, resulting in oppositely charged ions.

• Covalent Bond: Formed when atoms share pairs of electrons.

Example: Sodium chloride (NaCl) is formed by the transfer of an electron from sodium (metal) to chlorine (nonmetal), creating an ionic bond.

Measurements in Chemistry

SI Units

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

• 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 measurement. The number of significant digits reflects the certainty in the measured value.

• Rules: All nonzero digits are significant; zeros between nonzero digits are significant; leading zeros are not significant; trailing zeros in a decimal are significant.

• Example: 0.00450 has three significant figures.

Density

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

• Formula:

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

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