Chemical Formula

A Chemical Formula is a shorthand way to show the elements present in a compound and the exact number of atoms of each element.

• It's the "language" of chemistry, allowing scientists to quickly represent a substance.
  
  Key Concepts and Definitions
  

• a. Element: A pure substance that cannot be broken down into simpler substances by chemical means (e.g., Hydrogen (H), Oxygen (O)).

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• b. Compound: A substance formed when two or more different elements are chemically combined in a fixed ratio (e.g., Water (H2​O), Salt (NaCl)).

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• c. Chemical Symbol: A one or two-letter abbreviation for an element. The first letter is always capitalized (e.g., Carbon (C), Sodium (Na)).

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• d. Reading a Formula: The subscript number (written lower and smaller) indicates the number of atoms of the element immediately before it.

  • *Example: H2​O means 2 atoms of H and 1 atom of O (the '1' is never written).

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• e. Valency means the number of bonds an atom can make. It shows how many other atoms it can join with. *Example:  Hydrogen (H) → Valency 1 → can make 1 bond.

• Oxygen (O) → Valency 2 → can make 2 bonds.

• Nitrogen (N) → Valency 3 → can make 3 bonds.

• Carbon (C) → Valency 4 → can make 4 bonds.

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• Important Examples of Formulas:

  Name of Substance	Common Use	Chemical Formula
  Water	- Drinking, Solvent	${\text{ - H}}_2\text{O}$
  Carbon Dioxide	- Exhaled air, Fire extinguishers	${\text{ - CO}}_2$
  Common Salt	- Food seasoning	$\text{ - NaCl}$
  Sulphuric Acid	- Car batteries	${\text{ - H}}_2{\text{SO}}_4$
  Calcium Carbonate	- Limestone, Chalk	${\text{ - CaCO}}_3$
  Oxygen Gas	- Breathing	${\text{ - O}}_2$
  Ammonia	- Household cleaner	${\text{ - NH}}_3$
  Sodium Hydroxide	- Making soap and paper (a base)	$\text{ - NaOH}$