matter|| molecular weight || atom || an atom of an element is electrically neutral

 Matter

Q1. What is the name of position where electrons are situated?

Ans:

The position where electrons are situated is called shell. 

Q2. What is meant by shell or energy level.

Ans:

The electrons in an atom are always moving around the nucleus in a fixed path is called shell or energy. The number of electrons present in it is called by 2n² rule. 

Q3. Write down the importance of an atom.

Ans:

A molecule is formed by the combination of atoms. Similarly, different molecules combine to form a new matter. Matters combine or decompose chemically to form a new substance. Atoms of the respective matters are the ones which participate in the chemical reaction.

Q4. An Atom of an element is electrically neutral, why?

Ans:

An atom of an element consists of equal number of protons (positively charged particles) and electrons (negatively charged particles). So, the total positive charges of protons neutralizes the total negative charge of electrons. Therefore, an atom of an element is electrically neutral.

Q5. What is the difference between an atom and a compound?
Ans:

Atom	Compound
An atom is the smallest particle of an element which take part in chemical reaction.	A compound is a pure substance formed by the chemical combination of two or more elements in a fixed proportion.
An atom is unstable.	A compound is stable.
An atom consists of electrons, protons and neutrons.	A compound consists of molecules or atoms.

Q6. What is meant by atomic mass unit (amu)?
Ans:

The unit used to measure the mass of an atom or atomic particle is called atomic mass unit (amu).

Q7. What is meant by 2H₂ and 2H?

Ans:

Here, 2H₂ means two molecules of hydrogen and 2H means two atoms of hydrogen.

Q8. Write the formula to calculate atomic weight and atomic number.

Ans:

Here, atomic weight = number of proton + number of neutron

i.e. at. wt. = P⁺ + n^o

and, atomic number = number of proton = number of electron.

i.e. z = p⁺ = e^-

Q9. Distinguish between atomic number and atomic weight.

Ans:

Atomic Number	Atomic Weight
The number of electron or proton in an atom is atomic number.	The sum of number of proton and neutron is atomic weight.
Its formula is Z = p+ = e-	Its formula is at. wt. = P+ + no

Q10. What does 2n² rule indicate? Write with example.

Ans:

2n² rule indicates the maximum number of electrons present in each of the sheel or an atom, where 'n' is the number of orbit.

For example:

For K - shell (n=1), the number of electrons = 2n² = 2x1² = 2

For L - shell (n=2), the number of electrons = 2n² = 2x2² = 8

For M - shell (n=3), the number of electrons = 2n² = 2x3² = 18

For N - shell (n=4), the number of electrons = 2n² = 2x4² = 32

Q11. What is symbol? Write the symbol of the elements; Helium, boron, Magnesium and Sodium.

Ans:

A symbol is a short form of an atom or a molecule.

Element	Symbol
Helium	He
Boron	B
Magnesium	Mg
Sodium	Na

Q12. What is valency?

Ans:

The number that determines the combining capacity of an element is called valency.

Q13. What are valence electrons?

Ans:

The number of electrons present in the outer most shell of an atom is called valence electrons.

Q14. What is meant by molecular formula?

Ans:

The group of symbol to denote the element or compound for any chemical substance is called molecular formula.

Q15. What is meant by molecular weights?

Ans:

The sum of the atomic weights of all the atoms of the same or different elements present in a molecule is called molecular weight. The molecular weight can be calculated by adding the atomic weights of elements present in a molecule.

Q16. What do you mean by duplet and octet?
Ans:
Duplet: The condition of attaining two electrons in the outermost orbit of Helium (he) is called duplet.
Octet: The condition of attaining eight electrons in the outermost orbit of noble gases, is called octet.

Labels:

Matter, atom, difference between element and atom, element, nucleus, atomic number and atomic weight, molecule, science8, science 8, science, molecular weight, duplet, octet, molecular formula, valency, 2n2 rule, atomic mass unit, electron, proton,