Tamil Nadu Board Class 7 Science Chapter 4 Atomic Structure

if you are looking for Tamil Nadu Board Class 7 Science Chapter 4 Atomic Structure then you are at the right place. Here we are providing solutions as well as additional QA / Important Notes.

 

[I] Choose the appropriate answer.

 

[1] The basic unit of matter is

1. element
2. molecule
3. atom [answer]
4. electron

 

[2] The sub-atomic particle which revolves around the nucleus is

1. atom
2. electron [answer]
3. Proton
4. neutron

 

[3] ………is positively charged.

1. proton [answer]
2. electron
3. molecule
4. neutron

 

[4] The atomic number of an atom is the

1. number of neutrons
2. number of protons [answer]
3. total number of protons and neutrons
4. number of atoms

 

[5] Nucleons comprises of

1. protons and electrons
2. neutrons and electrons
3. protons and neutrons [answer]
4. neutrons and positron

 

[II] Fill in the blanks.

1. The smaller particles found in the atom are called…….[subatomic particles]
2. The nucleus has………and………….[protons and neutrons.]
3. The …………revolve around the nucleus.[electrons]
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 is….2…..

 

[III] Match the following.

• Valency          Fe
• Neutral particle  proton
• iron   electrons in the outermost orbit
• hydrogen    neutron
• positively charged particle     monovalent

 

Solution – Match the following.

•  Valency – electrons in the outermost orbit
•  Neutral particle – neutron
•  Iron – Fe
•  Hydrogen – monovalent
•  Positively charged particle – proton

 

[IV] State true or false. If false, correct the statement.

1. The basic unit of an element is molecule.[FALSE – The basic unit of an element is atom.]
2. The electrons are positively charged.[FALSE – The electrons are negatively charged.]
3. An atom is electrically neutral.[TRUE]
4. The nucleus is surrounded by protons.[FALSE – The nucleus is surrounded by electrons.]

 

[V] Complete the analogy.

1. Sun: Nucleus :: Planets:Electrons
2. Atomic number :Number of protons::Mass number: Number of protons and neutrons.
3. K: Potassium :: C:Carbon

 

[VI] Consider the following statements and choose the correct option.

1. Assertion: An atom is electrically neutral.

Reason: Atoms have equal number of protons and electrons.

 

Both the assertion and reason are correct, and the reason is the correct explanation for the assertion.

 

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

Reason: The nucleus is at the centre.

 

Both the assertion and reason are correct, but the reason is not the correct explanation for the assertion.

 

3. Assertion: The number of protons or the number of neutrons is known as atomic number.

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

The assertion is incorrect, but the reason is correct.

 

[VII] Answer very briefly.

1. Define – Atom.

An atom is the smallest unit of an element that retains its chemical properties and consists of a nucleus surrounded by electrons.

 

2. Name the sub-atomic particles.

The sub-atomic particles are electrons, protons, and neutrons.

 

3. What is atomic number?

The atomic number is the number of protons in the nucleus of an atom.

 

4. What are the characteristics of proton?

Protons are positively charged particles found in the nucleus of an atom. They have a relative charge of +1 and a mass approximately equal to that of a neutron.