Matter and Its Classification

Definition of Matter

Matter is defined as anything that has mass and occupies space. All physical substances in the universe are forms of matter.

• States of Matter: Matter exists in three primary states: solid, liquid, and gas.

• Solids: Have a definite shape and volume.

• Liquids: Have a definite volume but take the shape of their container.

• Gases: Have neither definite shape nor volume; they expand to fill their container.

Classification of Substances

• Pure Substance: A material with a fixed composition and distinct properties.

• Element: A pure substance that cannot be broken down into simpler substances by chemical means (e.g., hydrogen, oxygen).

• Compound: A pure substance composed of two or more elements chemically combined in fixed proportions (e.g., water (H2O), carbon dioxide (CO2)).

Example: Table salt (NaCl) is a compound formed from sodium (Na) and chlorine (Cl).

The Periodic Table and Atomic Structure

The Periodic Table

The periodic table organizes all known elements by increasing atomic number (number of protons). Elements are arranged in rows (periods) and columns (groups) based on recurring chemical properties.

• Atomic Number: The number of protons in the nucleus of an atom; unique to each element.

Structure of the Atom

• Atoms are 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.

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

Chemical Bonds

Ionic Bonds

Ionic bonds are formed when electrons are transferred from one atom to another, typically between a metal and a nonmetal. This transfer creates positively charged ions (cations) and negatively charged ions (anions) that are held together by electrostatic attraction.

• Example: Sodium chloride (NaCl) forms when sodium (a metal) donates an electron to chlorine (a nonmetal).

Covalent Bonds

Covalent bonds occur when two atoms share one or more pairs of electrons. This type of bonding usually occurs between nonmetal atoms.

• Example: In water (H2O), each hydrogen atom shares an electron with the oxygen atom.

Measurements in Chemistry

SI Units

The International System of Units (SI) is the standard for scientific measurements. The main SI units used in 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 the amount of substance

Significant Figures

Significant figures indicate the precision of a measured quantity. The number of significant figures reflects the certainty in the measurement.

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant; trailing zeros in a decimal number are significant.

Example: The number 0.00450 has three significant figures.

Density

Density is a physical property defined as the mass of a substance divided by its volume.

Formula:

• d: Density (typically in g/cm3 or kg/m3)

• m: Mass

• V: Volume

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