Que 1- what are molecules ? Give an account of the arrangement of the constituent atoms in the molecules.
Ans– A molecule is the smallest-particle of an element or of a compound which is stable
under ordinary conditions and can exist freely and shows all the properties of that element
or compound .
A molecule may be made up of one, two or more atoms.Molecules with only one atom are called monoatomic, e.g., helium, argon, neon.
Molecules with two atoms are diatomic. These may have similar or different atoms, e.g.,
chlorine (Cl2), oxygen (02), hydrochloric acid gas (HCI).
Similarly, there are molecules containing three atoms (H2O, CO2), four atoms (P4, NH3) and so on.
The atoms in a molecule are chemically bonded in a definite pattern. This arrangement of atoms is given by the structural formula of the compound. For example, structural formula for water is H–O–H. This is a simple illustration for the structure of water. In fact water and all other molecules exhibit definite spatial arrangements depending on the nature of chemical bonding between atoms.
Que 2 –What do you understand by formula of a molecule ?
Ans- A group of atomic symbols, representing one molecule of a chemical substance is
known as formula.
Que 3 – Could you make a distinction between a molecule and a compound ?
Ans– A molecule is usually formed when at least two atoms of the same or different kinds combine. If two or three atoms of the same kind of element combine, then it is referred to as molecule of an element or simply molecule. For example, molecule of oxygen (02) is formed by the combination of two oxygen atoms.
Molecule formed by the union of two or more atoms of different elements is called a molecule of a compound or simply compound. For example, a molecule or a compound of carbon dioxide is formed by the union of one carbon atom and two oxygen atoms. However, the noble gases consists of molecules of single atoms only. For example, helium exists as He.
Que 4 – Comment on the statement. “A molecule is the smallest particle of a substance
(element or compound) which has the properties of the substance and is stable.”
Ans– Yes, it is true that a molecule is the smallest particle of a substance which has the properties of that substance and is stable. In case of gases like oxygen, a molecule (02) is stable and gives properties of oxygen gas, whereas atom O’ is not stable and does not represent oxygen gas.
In case of noble gases such as helium, a molecule is of monoatomic helium atom (He) and represents helium gas and is also stable. In case of a compound, e.g., carbon dioxide, properties of carbon dioxide molecule are the properties of carbon dioxide gas.A molecule of carbon dioxide is stable
Que 4-What is the difference between :
(i) an atom of hydrogen and a molecule of hydrogen ?
(ii) a molecule of oxygen and a molecule of water ?
Ans- (i) An atom of hydrogen is the smallest particle of hydrogen element which does not have independent existence. A molecule of hydrogen has two hydrogen atoms bonded together and is the smallest particle of hydrogen element which has independent existence.
(ii) A molecule of oxygen has two atoms and is the smallest particle of oxygen element which can exist independently. A molecule of water is a compound obtained from two hydrogen atoms and one oxygen atom.
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