Topic 1 of 7Aga Khan Board

Fundamentals of Chemistry

Atoms, elements, and compounds

Chemistry is the study of matter and how it changes. Every atom has a nucleus containing protons (positive) and neutrons (no charge). Orbiting the nucleus are electrons (negative). The number of protons is the atomic number.

The Periodic Table organizes all 118 known elements by increasing atomic number. Elements in the same group (vertical column) share similar chemical properties. Elements in the same period (horizontal row) have the same number of electron shells.

Chemical bonding happens when atoms join together:

Ionic bonding — a metal transfers electrons to a non-metal, creating oppositely charged ions that attract each other. Example: NaCl (table salt).

Covalent bonding — two non-metals share electrons. Example: H₂ gas.

States of matter describe how particles are arranged:

Solid: particles packed tightly, fixed shape

Liquid: particles close but can flow

Gas: particles far apart, move freely

Changing state requires energy. Melting and boiling absorb energy. Freezing and condensation release energy.

Key Points to Remember

1Atomic structure
2Periodic table
3Chemical bonding
4States of matter

Pakistan Example

Salt in Your Biryani — Ionic Bonding in Every Kitchen

The table salt (NaCl) in Karachi-style biryani is ionic bonding in action. Sodium donates an electron to chlorine, creating Na⁺ and Cl⁻ ions. This ionic crystal dissolves in the curry base, releasing ions and giving biryani its salty taste.

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Chemical Bonding