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, each with distinct physical 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.

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

Pure Substances and Mixtures

A pure substance has a fixed composition and distinct properties. Pure substances are classified as elements or 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 in fixed proportions. Examples: Water (H2O), Carbon dioxide (CO2).

Mixtures are not mentioned directly, but for completeness: mixtures are combinations of two or more substances that retain their individual properties.

Additional info: Mixtures can be homogeneous (uniform composition) or heterogeneous (non-uniform composition).

Atomic Structure and the Periodic Table

Atoms and Subatomic Particles

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

• Proton: Positively charged particle located in the nucleus.

• Neutron: Neutral particle located in the nucleus.

• Electron: Negatively charged particle orbiting the nucleus.

The nucleus contains protons and neutrons, while electrons move in regions around the nucleus.

The Periodic Table

The periodic table organizes elements by their atomic number (number of protons). It provides information about element properties and relationships.

• Atomic Number: Number of protons in an atom; determines the element's identity.

• Example: Carbon has atomic number 6, meaning it has 6 protons.

Chemical Bonds

Ionic and Covalent Bonds

Chemical bonds are forces that hold atoms together in compounds.

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

• Covalent Bond: Formed when atoms share pairs of electrons, typically between nonmetals.

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

Measurement and Units

SI Units

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

• Example: 0.00450 has three significant figures.

Density

Density is a physical property defined as mass per unit volume. It is used to characterize substances and identify materials.

• Formula:

• Where: d = density, m = mass, V = volume

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