Chemical Symbols, Formulae and Valency
🎯 What will you learn in this lesson?
👉 What a chemical symbol is and how it is written.
👉 What chemical formulae of elements and compounds represent.
👉 The basic meaning of valency.
👉 How symbols such as H, O, Na and Cl are related to chemical formulae such as H₂ and O₂.
🔹 Atom
An atom is the smallest unit of an element that takes part in chemical reactions while retaining the identity of that element.
To represent elements conveniently, their names are abbreviated using chemical symbols. Each element has its own symbol.
Chemical Symbol
A chemical symbol is a short form used to represent an element. In other words, the symbol represents one atom of that element in a chemical expression.
⭐ Rules and common methods used for writing chemical symbols ⭐
Using the first letter of the English name of an element:
Hydrogen (Hydrogen) = H
Oxygen (Oxygen) = O
Carbon (Carbon) = C
Nitrogen (Nitrogen) = N
Sulfur (Sulfur) = S
Boron (Boron) = B
When several elements begin with the same letter, a second letter is used to distinguish them. The first letter is uppercase and the second letter is lowercase:
Calcium (Calcium) = Ca
Chromium (Chromium) = Cr
Chlorine (Chlorine) = Cl
Cadmium (Cadmium) = Cd
Cesium (Cesium) = Cs
Bromine (Bromine) = Br
Bismuth (Bismuth) = Bi
Barium (Barium) = Ba
Beryllium (Beryllium) = Be
Some chemical symbols come from the Latin or historical names of elements:
Sodium (Natrium) = Na
Potassium (Kalium) = K
Iron (Ferrum) = Fe
Lead (Plumbum) = Pb
Silver (Argentum) = Ag
Gold (Aurum) = Au
Copper (Cuprum) = Cu
Mercury (Hydrargyrum) = Hg
Match the left column with the right one
👉 Significance of a Chemical Symbol
⭐ A symbol provides a short and universal representation of an element.
⭐ A chemical symbol can represent one atom of an element in a chemical expression.
⭐ A symbol is also used together with atomic or molar quantities in chemical calculations.
⭐ For elements that exist as individual atoms under ordinary conditions, such as calcium (Ca), sodium (Na), potassium (K) and iron (Fe), the symbol is commonly used to represent the element and an individual atom of it.
🔹 Molecule
A molecule is a particle made of one or more atoms chemically bonded together that can exist independently and has the characteristic chemical properties of the substance.
Chemical Formula
A chemical formula uses the symbols of elements to represent the composition of a substance.
⭐ When a molecule contains more than one atom of the same element, the number of atoms is written as a subscript to the lower right of the symbol.
Hydrogen (H) – H2, Oxygen (O) – O2, Ozone (O) – O3
To understand chemical formulae properly, it is also important to understand valency and, in later lessons, ions or radicals.
Valency
The combining capacity of an atom or ion is called its valency.
At an introductory level, valency can be understood by comparing how many hydrogen atoms an atom can combine with, or how many hydrogen atoms it can replace in a compound.
⭐ Valency is generally expressed as a whole number, not as a fraction.
⭐ Some elements can show more than one valency in different compounds.
✅ Quick Revision
🔹 A chemical symbol is a short form used to represent an element.
🔹 A chemical formula uses element symbols and subscripts to represent the composition of a substance.
🔹 Valency is the combining capacity of an atom or ion.
🔹 The first letter of a chemical symbol is uppercase and the second letter, if present, is lowercase.
🔹 Correct valencies help us write and understand the chemical formulae of compounds.
