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 physical states, each with distinct properties.

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

• Liquid: Has a definite volume but takes the shape of its container; particles are close but can move past one another.

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

Classification of Matter

Matter can be classified based on its composition:

• Pure Substance: Has a fixed composition and distinct properties. Examples include elements and compounds.

• Element: A substance that cannot be broken down into simpler substances by chemical means. Examples: O2, Fe.

• Compound: Consists of two or more elements chemically combined in fixed proportions. Examples: H2O (water), CO2 (carbon dioxide).

Example: Water (H2O) is a compound because it contains hydrogen and oxygen chemically bonded in a 2:1 ratio.

Atomic Structure and the Periodic Table

Structure of the Atom

Atoms are the basic units of matter, composed of three fundamental 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 clouds or shells.

The nucleus is the dense center of the atom, containing protons and neutrons, while electrons move in regions around the nucleus.

The Periodic Table

The periodic table is a systematic arrangement of elements in order of increasing atomic number (number of protons). It helps predict element properties and chemical behavior.

• Groups: Vertical columns with similar chemical properties.

• Periods: Horizontal rows indicating energy levels.

Example: Sodium (Na) and potassium (K) are in the same group and share similar reactivity.

Chemical Bonding

Ionic and Covalent Bonds

Chemical bonds are forces that hold atoms together in compounds. The two main types are:

• Ionic Bonds: Formed by the transfer of electrons from a metal to a nonmetal, resulting in oppositely charged ions that attract each other.

• Covalent Bonds: Formed when two nonmetal atoms share one or more pairs of electrons.

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

Measurement in Chemistry

SI Units

The International System of Units (SI) is the standard for scientific measurements. Key SI base units include:

• Meter (m): Length

• Kilogram (kg): Mass

• Second (s): Time

• Kelvin (K): Temperature

• Mole (mol): Amount of substance

Significant Figures

Significant figures (sig figs) indicate the precision of a measured value. The number of significant digits 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 mass per unit volume. It is useful for identifying substances and predicting whether an object will float or sink in a fluid.

• Formula:

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

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