HBSE 9th Class Science Notes Chapter 3 Atoms and Molecules

Haryana State Board HBSE 9th Class Science Notes Chapter 3 Atoms and Molecules Notes.

Haryana Board 9th Class Science Notes Chapter 3 Atoms and Molecules

→ Any compound is composed of two or more than two elements.

→ In a compound of water, the ratio of masses of hydrogen and oxygen is always 1: 8, it does not concern whether which source does the water belong to.

→ In ammonia (NH3), Nitrogen and Hydrogen always exist in the ratio of 14: 3 according to their masses.

→ John Dalton was bom in 1766 in England.

→ In a compound, the relative number of atoms and its type are definite.

→ The structural unit of all the fluids is atom.

HBSE 9th Class Science Notes Chapter 3 Atoms and Molecules

→ The atomic radius is measured in nanometre (nm). (1nm = 10-9m)

→ Nowadays the International Union of Pure and Applied Chemistry (IUPAC) approves names of elements.

→ Each element have a name and an unmatched chemical symbol.

→ Each element has a characteristic atomic mass.

→ We assume unit of atomic mass equal to that of the mass of a carbon atom.

→ Atomic masses of all the elements are obtained in relation to single atomic mass of isotope of carbon-12

→ Generally, a molecule is a group of two or more than two atoms which are interlinked by a chemical bond.

→ Molecules of an element are composed of only one kind of atoms.

→ Molecule with negative charge is called as electron and the molecule with positive charge is called as proton.

→ The chemical formulae of molecular compound are based on by means of combination of each element.

→ In ionic compounds, chemical formulae of compound are learnt by the number of electrons on each of the ions.

→ The number of particles (atoms, molecules or ions) in a mole of a substance is constant whose mass is 6.022 × 1023.

→ Law of Conservation of Mass: According to the law of conservation of mass, in a chemical reaction mass can neither be created, nor destroyed.

→ Law of Constant Proportions: In a pure chemical compound, elements always exist in constant proportions of masses, it is called the law of constant proportions.

→ Atom: The smallest particle of an element is atom, which can exist independently and it exhibits all its chemical properties.

→ Molecule: Molecule is that minute particle of an element or compound which can remain in a free state in normal conditions. It exhibits all properties of matter.

→ Relative Atomic Mass Unit: 1/12th part of atomic mass of an atom of carbon-12 isotopes is taken to be the relative atomic mass unit.

→ Atomicity: The number of atoms being used in structural formation of any molecule is called atomicity of its molecule.

HBSE 9th Class Science Notes Chapter 3 Atoms and Molecules

→ Ions: Compounds are composed of metals and non-metals contain charged particles. These charged particles are called as ions e.g. sodium, magnisium.

→ Polyatomic Ions: A group of atoms that behave as an ion are called polyatomic ions.

→ Chemical Formula: The chemical formula of a compound is a symbolic representation of its composition.

→ Valency: The combining power (or capacity) of an element is the valency of that element.

→ Binary Compounds: The simplest compounds formed by combination of two different elements are known as binary compounds.

→ Molecular Mass: Molecular mass is the sum total of masses of overall combined atoms of matter. It is expressed by atomic mass units (u).

→ Formula Unit Mass: Formula unit mass of a substance is a sum total of atomic masses of its whole combined atoms.

→ Mole: Mole is that quantity of a substance in which the number of particles (atom, ion, molecule or formula unit) is equal to the existing atoms in exactly 12g of carbon =12.

→ Molar Mass: Mass of molecules of a single mole of a substance is called its molar mass.

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