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 fixed shape; particles are close but can move past one another.

• Gas: No definite shape or 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 (e.g., hydrogen, oxygen).

• Compounds: Substances composed of two or more elements chemically combined in fixed proportions (e.g., water, H2O; carbon dioxide, CO2).

Mixtures are combinations of two or more substances that retain their individual properties and can be separated by physical means.

Atomic Structure and the Periodic Table

Atoms and Subatomic Particles

Atoms are the basic units of matter, consisting of three main subatomic 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): Length

• Kilogram (kg): Mass

• Second (s): Time

• Kelvin (K): Temperature

• Mole (mol): Amount of substance

Significant Figures

Significant figures indicate the precision of a measured quantity. The number of significant figures in a measurement includes all known digits plus one estimated digit.

• When multiplying or dividing, the result should have the same number of significant figures as the measurement with the fewest significant figures.

• When adding or subtracting, the result should have the same number of decimal places as the measurement with the fewest decimal places.

Density

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

• d: Density (e.g., g/cm3 or kg/m3)

• m: Mass

• V: Volume

Example: If a sample has a mass of 10.0 g and a volume of 2.0 cm3, its density is .