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: Definite shape and volume; particles are closely packed in a fixed arrangement.

• Liquid: Definite volume but no definite shape; particles are close but can move past one another.

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

Pure Substances and Mixtures

Pure substances have a fixed composition and distinct properties. They are classified as:

• Elements: Substances that cannot be broken down into simpler substances by chemical means. Examples include hydrogen (H) and oxygen (O).

• Compounds: Substances composed of two or more elements chemically combined in fixed proportions. Examples include water (H2O) and carbon dioxide (CO2).

Mixtures, by contrast, consist of two or more substances physically combined and can be separated by physical means.

Atomic Structure and the Periodic Table

Atoms and Subatomic Particles

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

• Protons: Positively charged particles located in the nucleus.

• Neutrons: Neutral particles also found in the nucleus.

• Electrons: Negatively charged particles that orbit the nucleus in electron clouds.

The Periodic Table

The periodic table organizes elements by increasing atomic number (number of protons). It groups elements with similar chemical properties into columns called groups or families.

Chemical Bonds

Ionic and Covalent Bonds

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

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

• Covalent Bonds: Formed when two atoms (usually nonmetals) share one or more pairs of electrons.

Example: Sodium chloride (NaCl) forms via ionic bonding, while water (H2O) forms via covalent bonding.

Measurement in Chemistry

SI Units

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

• 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 reflect the precision of a measured quantity. The number of significant figures in a measurement includes all certain digits plus one uncertain digit.

• Rules: 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.

Density

Density is a physical property defined as mass per unit volume. It is calculated using the formula:

• d: Density (e.g., g/cm3)

• m: Mass (e.g., grams)

• V: Volume (e.g., cm3 or mL)

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