Extra Questions for Class 9 Science Chapter 4 Structure of Atom
Here we are providing extra questions for class 9 science chapter 4 structure of atom. These questions are important for exam as well. You will be able to score more in your exams by practicing these questions.
Very Short Answer Type Question (VSA)
Q.1. In Rutherford’s model of an atom, fast moving alpha (a)-particles were made to fall on a
thin gold foil. State two properties of a-particles.
AnswerAnswer: (a) Alpha particles are positively charged particles.
(b) They are doubly charged helium ions having a mass number of 4 (consists of 2 protons and 2 neutrons).
Q.2. What will be the charge on an atom with mass number one and atomic number one?
AnswerAnswer: The atom will not carry any charge because the atom contains one unit negative charge in the form of electron and one unit positive charge in the form of a proton.
Q.3. What characteristic feature is seen in the configurations of chemically inactive elements?
AnswerAnswer: Chemically inactive elements have 8 electrons in their valence shell except helium which has 2 electrons in its valence shell which is the maximum capacity of K shell.
Q.4. Atomic number is defined in terms of protons and not in terms of electrons. Why?
AnswerAnswer: An atom may lose or gain electrons, but the number of protons remains constant till the same atom exist.
Q.5. An oxide of an element Z has a formula Z2O3.
(a) How many electrons are there in the outermost shell of an atom of element Z?
(b) Write down the formula for the chloride of Z.
AnswerAnswer: (a) An ion of element Z has the formula Z3+. Hence, it has 3 valence electrons.
Q.6. Why are anode rays also called canal rays?
AnswerAnswer: Canal rays are positively charged anode rays. The canal rays are called so because they pass through the holes or the canals in the cathode.
Q.7. Neutrons can be found in all atomic nuclei except in one case. Which is this atomic nucleus
and what does it consist of?
AnswerAnswer: In case of hydrogen atom, there is no neutron. It consists of only one proton.
Q.8. What would you conclude from the observation that cathode rays rotate a light paddle wheel placed in their path?
AnswerAnswer: When a light paddle wheel is placed in the path of cathode rays, the blades of the paddle wheel begin to rotate. It shows that cathode rays consist of material particles having mass and velocity.
Q.9. Find valencies of the elements having atomic numbers 10 and 15.
AnswerAnswer: 0 and 3
Short Answer Type Questions
Q.1. The atom of an element has 9 protons, 9 electrons and 10 neutrons.
(a) What is the atomic number of the element?
(b) What is the mass number of the element?
(c) Name the element and give its electronic configuration.
(d) Predict the valency of the element.
AnswerAnswer: (a) The atomic no. of element = No. of protons = 9
(b) The mass no. of element = No. of protons + No. of neutrons = 9 + 10 = 19
(c) The element with Z = 9 is fluorine (F). Its electronic configuration : 2, 7.
(d) The valency of fluorine is 1 and is calculated as 8 – 7 = 1.
Q.2. Element X has a proton number of 7. It also has seven neutrons.
(a) Deduce the number of electrons and the nucleon number of X.
(b) Represent X by writing the chemical symbol, including the proton and nucleon numbers.
AnswerAnswer: p = 7, n = 7 (a) Number of electrons = Number of protons = 7
Number of nucleons = number of p + number of n = 7 + 7 = 14
Q.3. Draw Bohr ’s model of an atom with three shells. How many electrons L-shell can accommodate?
AnswerAnswer: Number of electrons in L-shell = 8
Q.4. Justify the statement ‘atomic number of an element is equal to the number of electrons in a neutral atom only and not in anion’.
AnswerAnswer: In neutral atom, No. of protons = No. of electrons = Atomic number
An anion is formed by gain of one or more electrons by an atom. Therefore, anion contains more electrons than neutral atom or in other words number of electrons in anion is greater than atomic number (the number of protons).
Q.5. (a) If the number of electrons in an ion is 10 and the number of protons is 9, then
(i) what would be the atomic number of the ion?
(ii) what is the charge on the ion?
(b) An ion M2+ contains 10 electrons and 12 neutrons. What is the atomic number and
mass number of the element M? Name the element.
AnswerAnswer: (a) (i) Atomic number (Z) = No. of protons = 9
(ii) Charge on the ion = –1
Here, one electron is more than proton. So this one extra electron attains –1 charge on the ion.
(b) No. of electrons in M2+ ion = 10
Atomic number of atom M = 10 + 2 = 12
No. of protons in atom M = 12
Mass number of atom M = No. of protons + No. of neutrons = 12 + 12 = 24
The element M with atomic number 12 is magnesium (Mg).