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: 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.

Example: Water can exist as ice (solid), liquid water, or steam (gas).

Classification of Matter

Matter can be classified as pure substances or mixtures. Pure substances have a fixed composition, while mixtures contain two or more substances physically combined.

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

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

Example: Table salt (NaCl) is a compound; air is a mixture.

Atomic Structure and the Periodic Table

Atoms and Subatomic Particles

An atom is the basic unit of an element, consisting 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.

Example: A carbon atom has 6 protons, 6 neutrons, and 6 electrons.

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 the nucleus; determines the element's identity.

• Groups: Vertical columns; elements in the same group have similar chemical properties.

• Periods: Horizontal rows; elements in the same period have the same number of electron shells.

Example: Sodium (Na) is in group 1, period 3.

Chemical Bonding

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 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.

Measurements in Chemistry

SI Units

The International System of Units (SI) is used for scientific measurements. The main SI units relevant to 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 amount of substance

Example: The mass of a sample may be measured in kilograms; temperature in kelvin.

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.

• Application: When performing calculations, the result should reflect the least number of significant figures from the input values.

Example: 0.00450 has three significant figures.

Density

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

• 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 .