Page 45 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

5. Acids, Bases and Salts

Chapter in a Nutshell

v Anything that has mass and occupies space is called matter.
v The smallest particle of matter that cannot be further divided is called an atom.

v Atoms when combine with other atoms of the same or different kind, held together by

chemical forces form a molecule.
v An element is a pure substance made up of only one kind of atoms. It is the simplest form of

a pure substance that cannot be broken down into more simpler substances. For example,

gold, silver, aluminium, hydrogen, oxygen, etc.
v The elements are represented by using abbreviation known as symbols that are standardised

by the International Union of Pure and Applied Chemistry (IUPAC).

v A compound is a pure substance formed by the chemical combination of two or more elements
in a fixed ratio by mass. The smallest unit of a compound is a molecule. for example, sodium

chloride is a compound made up of elements–sodium (Na) and chlorine (Cl).
v Just as elements, compounds are also represented by using the symbols of their constituent

elements.

v A mixture is an impure substance made by mixing two or more pure substances in any
proportion. For example, mixture of sand and salt.

v Mixtures can be of two types - homogeneous mixtures and heterogeneous mixtures.
v Homogeneous mixtures have a uniform composition throughout. They are also called

solutions. For example, lemonade is a homogeneous mixture of water, sugar and lemon.

v Heterogeneous mixtures are the mixtures with non-uniform composition. For example,
mixture of oil and water.

v The atoms of an element consist of charged particles. Positively charged particles are called

protons, while the negatively charged particles are called electrons.
v An atom is neutral as the number of protons and electrons are equal. But by certain chemical

activity, an atom may gain or lose electrons. Such atoms with excess or deficit of electrons

are called ions.
v If an atom gains an electron, it acquires a negative charge and is called a negative ion or an

onion. If an atom loses an electron, it acquires a positive charge and is called a positive ion
or a cation.

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