Tamilnadu Samacheer Kalvi 7th Science Solutions Term 1 Chapter 4 Atomic Structure

 

Tamilnadu Samacheer Kalvi 7th Science Solutions Term 1 Chapter 4 Atomic Structure

Samacheer Kalvi 7th Science Atomic Structure Textual Evaluation

I. Choose the appropriate answer :

Question 1.

The basic unit of matter is __________

(a) Element

(b) Atom

(c) Molecule

(d) Electron

Answer:

(b) Atom

Question 2.

The subatomic particle revolve around the nucleus is __________

(a) Atom

(b) Neutron

(c) Electron

(d) Proton

Answer:

(c) Electron

Question 3.

__________ is positively charged.

(a) Proton

(b) Electron

(c) Molecule

(d) Neutron

Answer:

(a) Proton

Question 4.

The atomic number of an atom is __________

(a) Number of neutrons

(b) Number of protons

(c) Total number of protons and neutrons

(d) Number of atoms

Answer:

(b) Number of protons

Question 5.

__________ Nucleons comprises of

(a) Protons and electrons

(b) Neutrons and electrons

(c) Protons and neutrons

(d) Neutrons and Positron

Answer:

(c) Protons and neutrons

II. Fill in the blanks

1.The smaller particles found in the atom is called _ sub-atomic particels

2.The nucleus has Protons and Neutrons

3.The electrons revolve around the nucleus.

4.If the valency of carbon is 4 and that of hydrogen is 1, then the molecular formula of methane is CH4

5.There are two electrons in the outermost orbit of the magnesium atom. Hence, the valency of magnesium _2_

III.  Match the following.

Valency - Electrons in the outermost orbit  

Neutral particle   -  Neutron  

Iron    - Fe

Hydrogen   - Monovalent

Positively charged particle   - Proton  

IV. True or False. If False, give the correct statement (T/F).

Question 1.

The basic unit of an element is molecule.

Answer: (False)

Correct statement: The basic unit of an element is atom.

Question 2.

The electrons are positively charged.

Answer: False.

Correct statement: The electrons are negatively charged.

Question 3.

An atom is electrically neutral.

Answer: True

Question 4.

The nucleus is surrounded by protons.

Answer: (False)

Correct statement: The nucleus is surrounded by electrons.

V. Complete the analogy.

Sun: Nucleus, planets: electrons

Atomic number: Number of protons  , Mass number: number of protons and neutrons.

K: Potassium, C: Carbon.

VI. Assertion and reason.

Question 1.

Assertion : An atom is electrically neutral.

Reason : Atoms have equal number of protons and electrons.

Answer:

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Question 2.

Assertion : The mass of an atom is the mass of nucleus.

Reason : The nucleus is at the centre.

Answer:

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Question 3.

Assertion : The number of protons and neutrons is atomic number.

Reason : The mass number is sum of protons and neutrons.

Answer:

Assertion is false but the reason is true statement.

Correct statement: The number of protons and neutrons is mass number.

VII. Give very short answer.

Question 1.

Define an atom.

Answer:

An atom is the smallest particle of a chemical element that retains its chemical properties.

Question 2.

Name the sub-atomic particles.

Answer:

Proton, Electron, Neutrons.

Question 3.

What is atomic number?

Answer:

The number of electrons or protons in an atom is called the atomic number of that atom. It is represented by the letter Z.

Question 4.

What is the characteristics of proton?

Answer:

The proton is the positively charged particle and its located in the nucleus.

Its positive Charge is of the same magnitude as that of the electron’s negative charge.

Question 5.

Why neutrons called neutral particles?

Answer:

Neutrons are the particles in an atom that have a neutral change (no charge).

They are not positive like protons.

They are not negative like electrons.

So they are called as neutral particles.

VIII. Give short answer.

Question 1.

Distinguish Isotopes from Isobar.

Answer:

Question 2.

What are the isotones give one example.

Isotones are the atoms of different elements with same number of neutrons.

136C Neutrons = 13-6 = 7

147C Neutrons = 13-6 = 7

Question 3.

Differentiate mass number from atomic number.

Answer:

Question 4.

The atomic number of an element is 9, it has 10 neutrons. Find the element from the periodic table. What will be its mass number?

Answer:

The element is Fluorine

Its mass number A

= n + p

= 10 + 9 = 19

∴Mass number of Fluorine = 19

Question 1.

Draw the atom structure 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.

Question 2.

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:

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

= 26

Question 3.

What are nucleons? Why are they so called? 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 :

(a) Nucleons (Proton and Neutrons) have same mass as if they were identical particles that differ only in their electric charge.

(b) The proton carries a charge +1 and the Neutron is neutral.

(c) The size nucleon is about 1 : 6 fm (Femto meters)

(d) The force that holds the nucleus together is very short range.

Question 4.

Define valency? What is the valency of the element with atomic number 8? What is the compound by the element with hydrogen.

Answer:

Valency is defined as the combining capacity of an element.

Valency of the element with atomic number : 8 Name of the element:

Oxygen : 0

Atomic number: 8

Valency : 2

Water (H2O) is the Oxide of Hydrogen and most familiar oxygen compound

X. Questions based on Higher Order Thinking Skills. :

Question 1.

An atom of an element has no electron, will that atom have any mass or not? Can 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 : He2+. It has 2 protons and 2 neutrons but no electrons.

Question 2.

Find 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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