[3 Marks Question]

Question 13 Marks

What is common salt? Name the elements present in it. Write the formula of common salt. What are the atomic number and the mass number of the elements? Write the ions in the compound.

Answer

Common salt is mostly sodium chloride. The ionic compound with the formula NaCl, representing equal proportions of sodium and chlorine.
Elements present is common salt: Sodium & Chlorine.
Formula of common salt: NaCl Atomic number and mass number of NaCl:
Atomic number of Na = 1 Atomic number of Cl = 17 Mass number of Na = 23
Mass number of Cl = 35
Ions present in the compound :
Sodium ion Na+ and Chloride ion Cl

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Question 23 Marks

An atom of an element has no electron. Will that atom have any mass or not? Can an atom exist without electron? If so then give example.

Answer

Atoms with no electron will have mass, because mass depends on number of Protons and Neutrons though it has no electron.
Atoms can exist without electrons, Matter is build out of neutrons, protons (+) and electrons (-). Matter becomes stable only if it is electrically neutral.
So atoms without electrons do exist and must have their own states (charged or uncharged transfered back and forth in their environment)
Example: $He ^{2+}$. It has 2 protons and 2 neutrons but no electrons.

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Question 33 Marks

Differentiate mass number from atomic number.

Answer

Sr. No.	Atomic number	Mass number
1.	The number of electrons or protons in an atom is called atomic number of that atom.	The number of protons and neutrons present is its nucleus is called mass number of that atom.
2.	It is represented by the letter Z	It is represented by the letter ‘A’.
3.	Example: Helium (He) has 2 protons and two electrons hence its atomic number will be 2.	Example: Sodium (Na) has 11 protons and 12 Neutrons hence its mass number A= 11 + 12 = 23

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Question 43 Marks

What are nucleons? Why are they called so? Write the properties of the nucleons.

Answer

Nucleons are sub-atomic particles (Protons and Neutrons) which are located in the nucleus of atoms.
Neutron and proton exist within the nucleus of the atom, together, they are called as nucleons.

Properties of Nucleons :

Nucleons (Proton and Neutrons) have same mass as if they were identical particles that differ only in their electric charge.
The proton carries a charge +1 and the Neutron is neutral.
The size nucleon is about 1: 6 fm (Femto meters)
The force that holds the nucleus together is very short range.

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Question 53 Marks

The atomic number and the mass number of an element is 26 and 56 respectively. Calculate the number of electrons, protons and neutrons in its atom. Draw the structure.

Answer

Given:

Atomic number A = 26
Mass number A = 56
No. of Protons P = ?
No. of Electrons = ?
No. of Neutrons N = ?
Name of the element is Iron (Fe)
No. of proton (P) = 26
Mass number A = n+p
56 = n = 26
n = 56-26
∴ No. of neutrons n = 30
In an element No. of protons and No. of electrons is equal.
∴No of electrons = no. of protons
= 26Structure of Iron:

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Question 63 Marks

Draw the structure of an atom and explain the position of the sub-atomic particles.

Answer

Structure of an atom.

Position of the subatomic – particles.
Atom consist of three sub-atomic.
Particles: 1. Protons, 2. Electrons, 3. Neutrons

The nucleus of the atom contains the protons (positively charged) and the neutrons (no change)
The outermost regions of the atom are called electron shells and contain the electrons (negatively charged)
The protons have a positive charge while neutrons have a neutral charge.
Electrons circle around the nucleus of an atom, they are negatively charged.

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