Revision: Language of Chemistry Chemistry ICSE ICSE Class 8 CISCE

Radical: A radical is an atom of an element or a group of atoms of different elements that behaves as a single unit with a positive or negative charge on it.

Alchemy was a form of chemistry studied in the middle age, which was concerned with trying to discover ways to change ordinary metals into gold.

Elements : An element is the basic form of matter that cannot be broken down into simpler substances by chemical reactions.

Compounds : A compound is a pure substance formed by the chemical combination of two or more elements in a fixed ratio by mass.

When the properties of elements in a period or a group of the modern periodic table are compared, certain regularity is observed in their variations. It is called the periodic trends in the modern periodic table.

The valency of an element is determined by the number of electrons present in the outermost shell of its atoms, that is, the valence electrons.

Molecular formula: It is a symbolic representation of a molecule. It shows the number of atoms of each element present in it. These atoms combine in whole number to form the molecule.

The reactions in which heat is absorbed are called endothermic reactions. The reactants absorb heat for form products.

A chemical equation is a balanced account of a chemical transaction. It is not merely a qualitative statement, but it also gives quantitative information of a chemical reaction.

OR

The representation of a chemical reaction in a condensed form using chemical formulae is called as the chemical equation.

Carbonic acid

• Word equations use names; chemical equations use formulas.
• Reactants → Products, with arrow showing reaction direction.
• Use + between two or more reactants or products.
• Show states: (s), (l), (g), (aq); use ↑ for gas, ↓ for precipitate.
• Heat (Δ) or other conditions go above/below the arrow.

• Law of Conservation of Mass: In a chemical reaction, mass is neither created nor destroyed, so the number of atoms of each element must be equal on both sides.
• A skeletal (unbalanced) equation has unequal atoms of one or more elements on the LHS and RHS.
• Balancing is done using the hit-and-trial method, starting with the compound having the most atoms and balancing hydrogen and oxygen last.
• Only coefficients are changed while balancing; chemical formulas must not be altered.
• A balanced equation may also indicate physical states (s, l, g, aq) and reaction conditions, such as temperature, pressure, or a catalyst.