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: solid, liquid, and gas.

• 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.

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), carbon (C).

• 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 and can be separated by physical means.

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:

• Protons: Positively charged particles located in the nucleus.

• Neutrons: Neutral particles also located in the nucleus.

• Electrons: Negatively charged particles that orbit the nucleus.

The Periodic Table

The periodic table organizes elements by their atomic number, which is the number of protons in the nucleus.

• Atomic Number (Z): Defines the identity of an element.

• Arrangement: Elements are arranged in rows (periods) and columns (groups) based on similar properties.

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 SI Units

SI Units

The International System of Units (SI) is used for scientific measurements.

• 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.

Density

Density is a physical property defined as mass per unit volume.

• Formula:

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

• Units: Commonly expressed in g/cm3 or kg/m3.

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