Key Points to Remember: Atoms and Molecules | Class 10 Science Chapter 7

Atoms and Molecules: Points to Remember

Isotopes

Two or more forms of an element having the same atomic number, but different mass number are called Isotopes.

Example: (³⁵₁₇Cl, ³⁷₁₇Cl)

Isobars

Atoms of different elements having the same mass number, but different atomic numbers are called Isobars.

Example: (⁴⁰₁₈Ar, ⁴⁰₂₀Ca)

Isotones

Atoms of different elements having the same number of neutrons, but different atomic number and different mass number are called Isotones.

Example: (¹³₆C, ¹⁴₇N)

Relative Atomic Mass

Relative atomic mass of an element is the ratio between the mass of one atom of the element to 1/12th of the mass of the atom of carbon -12.

Average Atomic Mass

Average atomic mass of an element is calculated by adding the masses of its isotopes, each multiplied by their natural abundance on the Earth.

Relative Molecular Mass

Relative molecular mass of a molecule is the ratio between the mass of one molecule of the substance to 1/12th of the mass of the atom of carbon – 12.

Avogadro’s Law

The Avogadro’s law states that “equal volumes of all gases under similar conditions of temperature and pressure contain equal number of molecules”.

Vapour Density

The vapour density is defined as “the ratio between the masses of equal volumes of a gas (or a vapour) and hydrogen under the same condition”.

Atomicity

Atomicity of a monoatomic element can be calculated using the formula:

Atomicity = Molecular mass / Atomic Mass

Molecular Mass & Vapour Density

The relationship between molecular mass and vapour density is:

Molecular mass = 2 × Vapour density

Important Points to Remember for Electricity | Science Class 10

Points to Remember - Electricity | Science

Electricity (Science) - Points to Remember

• The magnitude of current is defined as the rate of flow of charges in a conductor.
• The SI unit of electric current is ampere (A).
• The SI unit of electric potential and potential difference is volt (V).
• An electric circuit is a network of electrical components, which forms a continuous and closed path for an electric current to pass through it.
• The parameters of conductors like its length, area of cross-section and material, affect the resistance of the conductor.
• SI unit of electrical resistivity is ohm metre. The resistivity is a constant for a given material.
• The reciprocal of electrical resistivity of a material is called its electrical conductivity. \(\sigma = 1/\rho\)
• The passage of electric current through a wire results in the production of heat.
• This phenomenon is called heating effect of current.
• One horse power is equal to 746 watts.
• The function of a fuse wire or a MCB is to protect the house hold electrical appliances from excess current due to overloading or a short circuit.