Samacheer Kalvi 7th Science Term 1 Solutions Chapter 4 Pdf
Tamilnadu Board Samacheer Kalvi 7th Science Term 1 Solutions Chapter 4: Tamilnadu State Board Solution Class 7 Science Term 1 Chapter 4 – Atomic Structure.
Samacheer Kalvi 7th Science Term 1 Solutions Chapter 4: Overview
Board |
Samacheer Kalvi |
Class |
7 |
Subject |
Science |
Chapter |
4 |
Chapter Name |
Atomic Structure |
Samacheer Kalvi 7th Science Term 1 Solutions Chapter 4 Pdf
Atomic Structure
Chapter 4
I.) Choose the appropriate answer.
1.) The basic unit of matter is ________
a.) element
b.) atom
c.) molecule
d.) electron
Answer : b. atom
Solution : An atom is the smallest unit of an element that retains its chemical properties.
2.) The sub-atomic particle which revolves around the nucleus is _______
a.) atom
b.) neutron
c.) electron
d.) proton
Answer : c. electron
Solution : Electron is a negatively charged particle. Electron revolve around the nucleus of the atom in specific orbit.
3.) _______ is positively charged.
a.) Proton
b.) Electron
c.) Molecule
d.) Neutron
Answer : a. Proton
Solution : The proton is the positively charged particle and it is located at the nucleus.
4.) The atomic number of an atom is the _______
a.) number of neutrons
b.) number of protons
c.) total number of protons and neutrons
d.) number of atoms
Answer : b. number of protons
Solution : The number of electrons or protons in an atom is called the atomic number of that atom.It is represented by the letter Z.
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
Solution : The protons and neutrons are called nucleons.
II.) Fill in the blanks.
1.) The smaller particles found in the atom are called __sub atomic particle__.
2.) The nucleus has ____protons____and __neutron______ .
3.) The ___electron____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 is____2____ .
III.) Match the following.
Valency | Electrons in the
outermost orbit |
Neutral particle | Monovalent |
Iron | Fe |
Hydrogen | Proton |
Positively charged
particle |
Neutron |
IV.) State true or false. If false, correct the statement.
1.) The basic unit of an element is molecule.
Answer : False
Correct statement : The basic unit of an element is atom.
2.) The electrons are positively charged.
Answer : False
Correct statement : The electron are negatively charged particle.
3.) An atom is electrically neutral.
Answer : True
4.) The nucleus is surrounded by protons.
Answer : False
Correct statement : The nucleus is surrounded by electron.
IV.) State true or false. If false, correct the statement.
1.) The basic unit of an element is molecule.
Answer : False
Correct statement : The basic unit of an element is atom.
2.) The electrons are positively charged.
Answer : False
Correct statement : The electron are negatively charged particle.
3.) An atom is electrically neutral.
Answer : True
4.) The nucleus is surrounded by protons.
Answer : False
Correct statement : The nucleus is surrounded by electron.
V.) Complete the analogy.
1.) Sun : Nucleus :: Planets : _Electrons_
2.) Atomic number : __Number of protons or electron___ :: Mass number : Number of protons and neutrons.
3.) K: Potassium :: C : __Corban___.
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.
Answer : a. Both assertion and reason are true and reason is the correct explanation of assertion.
2.) Assertion: The mass of an atom is the mass of its nucleus.
Reason: The nucleus is at the centre.
Answer : a. Both assertion and reason are true and reason is the correct explanation of 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
Answer : d. Assertion is false but reason is true.
VII.) Answer very briefly.
1.) Define – Atom.
Answer : An atom is the smallest particle of an element that retains its chemical properties.
2.) Name the sub-atomic particles.
Answer : There are three sub atomic particles :
i] electron
ii] proton
iii] neutron
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.
4.) What are the characteristics of proton?
Answer : The characteristics of proton are :
i] The proton is the positively charged particle
ii] it is located at the nucleus
iii]Its positive charge is of the same magnitude as that of the
electron’s negative charge.
5.) Why neutrons are called neutral particles?
Answer : Neutrons are called neutral particles because they do not have any positive or negative charge like protons or electron.
VIII.) Answer briefly.
1.) Distinguish isotopes from isobar.
Answer :
Atoms that have same atomic number but different mass numbers are called isotopes. | Atoms that have the same mass number but different atomic numbers are called isobars. |
For example, hydrogen has three isotopes. They are: Proteum (1H1), Deuterium (1H2), Tritium (1H3). | For example: Calcium (20Ca40),
Argon (18Ar40). |
2.) What are isotones? Give one example.
Answer : Atoms of different elements that have same number of neutrons are called isotones. For example : 13 C6 and 14 C7 have same number of neutron.
13 C6 Neutrons = 13 – 6 = 7
14 C7 Neutrons = 14 – 7 = 7
3.) Differentiate mass number from atomic number.
Answer :
Mass Number |
Atomic Number |
The total number of protons and neutrons present in the nucleus of an atom is called its mass number | Atomic number is the number of protons in an atom. |
It is represented by the letter A. | It is represented by the letter Z. |
Eg : Lithium atom contains 3 protons and 4 neutrons. Its mass number (A) = 3+4 = 7 | Eg : lithium atom contain 3 protons and 3 electrons. Its atomic number (Z) = 3 |
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 = 1.
IX.) Answer in detail.
1.) Draw the structure of an atom and explain the position of the sub-atomic particles.
Answer :
Atom consists 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). Electrons circle around the nucleus of an atom, they are negatively charged.
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
3.) What are nucleons? Why are they called so? Write the properties of the nucleons.
Answer : Protons and neutrons are the two types of particles in the nucleus of an atom. They are called nucleons.
Proton and neutron exist within the nucleus together therefore, called nucleon.
Properties of Nucleons:
i] Nucleons have same mass as if they were identical particles that differ only in their electric charge.
ii] The proton carries a charge +1 and the neutrons are neutral.
iii] The size nucleon is about 1:6 fm (Femto meters)
iv] The force that holds the nucleus together is very short range.
4.) Define valency. What is the valency of the element with atomic number 8? What is the compound format by this element with hydrogen?
Answer : Valency is the combining property of an atom.
Valency of the element with atomic number : 8
Name of the element: oxygen : 0
Atomic number : 8
Valency : 2
Valency of hydrogen is 1 therefore , compound formula of hydrogen and oxygen is H2O
[water].
X.) Higher Order Thinking Skills.
1.) 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 : An atom of an element has no electron will have mass because mass depends on number of protons and neutron and not on electron.
An atom can exist without electron, Matter is build out of neutrons, protons (+) and electrons (-). Matter becomes stable only if it is electrically neutral. For example : Hydrogen atom without an electron and an alpha particle can be thought of as a Helium atom without electrons.
2.) 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 : Sodium chloride which are also called NaCl is the common salt where sodium and chlorine are the elements present in it.
Atomic number of Na = 1
Atomic number of CI = 17
Mass number of Na= 23
Mass number of CI = 35
lons present in the compound are Na+ve (1, 8, 1) and CI -ve (2, 8, 7).