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Class VII T1 U4 Science Atomic Structure Question -Answers
UNIT – 4 ATOMIC STRUCTURE
I. Choose the appropriate answer:
1. The basic unit of matter is ________.
a. element
b. atom
c. molecule
d. electron
Ans: b. Atom
2. The subatomic a particle which revolve around the nucleus is ________.
a. atom
b. neutron
c. electron
d. proton
Ans: c. electron
3. _________ is positively charged.
a. Proton
b. Electron
c. Molecule
d. Neutron
Ans: a. Proton
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
Ans: b. number of protons
5. Nucleons comprises of _____________.
a. protons and electrons
b. neutrons and electrons
c. protons and neutrons
d. neutrons and positron
Ans: c. protons and neutrons
II. Fill in the blanks.
1. The smaller particles found in the atom are called Subatomic particles.
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 is 2.
III. Match the following:
IV. 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.
Answer: Both 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: Both 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: Assertion is false but the Reason is true statement.
Correct statement: The number of protons and neutrons is mass number.
VII.Answer very briefly.
1. Define - A atom.
The atom is the smallest particle of a chemical element that retains its chemical properties.
2. Name the sub-atomic particles.
Proton, Electron, Neutrons.
3. What is atomic number?
The number of electrons or protons in an atom is called the atomic number of that atom. It is denoted by the letter Z.
4. What are the characteristics of proton?
The proton is the positively charged particle and it is located in the nucleus. Its positive charge is of the same magnitude as that of the electron’s negative charge.
5. Why neutrons called neutral particles?
Neutrons do not have any charge. So they are called neutral particles.
VIII. Answer briefly:
1. Distinguish Isotopes from Isobar.
2. What are isotones? Give one example.
Isotones are the atoms of different elements with same number of neutrons. 13 C6 Neutrons = 13 – 6 = 7
14 C7 Neutrons = 14 – 7 = 7
3. Differentiate mass number from atomic number.
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?
The element is Fluorine.
Its mass number A=n + p = 10 + 9 = 19
Mass number of Fluorine = 19
IX. Answer in detail.
1. Draw the structure of an atom and explain the position of the sub-atomic particles.
An atom is the smallest particle of an element that retains its chemical properties.
Atoms are too small to be seen by the naked eye or even through a microscope.
An atom consists of a dense nucleus which has positively-charged protons and electrically neutral neutrons.
Electrons,protons and neutrons are called subatomic particles.
Proton (p)
The proton is the positively charged particle and it is located at the nucleus. Its positive charge is of the same magnitude as that of the electron’s negative charge.
Neutron (n)
Neutron is inside the nucleus.
The neutron does not have any charge.
Except hydrogen (protium), the nucleus of all atoms contains neutrons. Protons and neutrons are the two types of particles in the nucleus of an atom. They are called nucleons.
Electron (e)
This is a negatively charged particle.
Electrons revolve around the nucleus of the atom in specific orbits.
The mass of an electron is negligible as compared to that of a proton or neutron.
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.
Atomic Number = Number of Protons or Number of electrons
Mass Number = Number of Protons + Number of Neutrons
Given:
Atomic number of an element = 26
Mass number of an element = 56
Atomic number / number of electron/ number of proton = 26
Number of Protons =?
A = n + p
Number of neutrons = Mass number - Number of protons
n = A - p
n = 56 - 26
= 30
Number of neutrons = 30
3. What are nucleons? Why are they called so? Write the properties of the nucleons.
The protons and neutrons are called nucleons, which are located in the nucleus of an atom.
Properties of Nucleons:
The proton carries a charge of +1 (in units of the electron charge) and the neutron is neutral (zero charge).
Both protons and neutrons have the same mass.
The size of the nucleon is about 0.0000000000000016 m.
4. Define valency. What is the valency of the element with atomic number 8? What is the compound format by this element with hydrogen?
Valency is defined as the combining property of an atom.
It is a measure of how many hydrogen atoms it can combine with.
When atoms of different elements combine with each other, molecules of compounds are formed.
Valency of the element with atomic number 8 = oxygen
The valency of oxygen = 2
Oxygen can combine with two atoms.
When a hydrogen atom combined with oxygen,it gives water molecule.
O2 + 2H2 → 2H2O
Water is a compound.
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.
Atoms with no electrons will also have mass, because mass depends on the number of protons and neutrons though it has no electron.
Yes, atoms can exist without electrons, matter is built out of neutrons, protons and electrons.
So atoms without electrons do exist and we call it as ions
2. What is common salt? Name the elements present in it. Write the formula of common salt. What are the atomic numbers and the mass number of the elements? Write the ions in the compound.
Sodium chloride is generally known as common salt.
Two elements namely, sodium and chlorine are there in sodium Chloride.
Molecular formula of Sodium Chloride is NaCl.
Atomic number of Na=11
Mass number of Na=23
Atomic number of Cl=17
Mass number of Cl=35
Ions in Sodium Chloride are Na+ and Cl-.
