Ques 1: Draw the atomic structure of the hydrogen atom.
K=1 electron (no neutron)Ques 2: Why are some elements chemically inert?
Ans: Because their outermost shell is completely filled.
Ques 3: Why is an atom electrically neutral?
Ans: It has same number of protons and electrons, (positive charge = negative charge).
Ques 4: What is the charge and mass of a-particles?
Ans: Charge is + 2
Mass is 4 a.m.u.
Ques 5: What are valence electrons?
Ans: Electrons present in the outermost shell of an atom are called valence electrons.
Ques 6: An atom has atomic number 12, what is its valency and name the element?
Ans: Atomic number = 12
∴ Protons = Electrons = 12 Electrons Configuration = K L M -2 8 2
∴ Valency = 2
Element is magnesium.
Ques 7: Find the number of neutrons in 2713X.
Ans: Mass number = 27
∴ p + n = 27 p = 13, (Atomic No. = Number of protons)
∴ 13 + n = 27
∴ n = 14
∴ Neutron =14
Ques 8: Where is the mass of atom concentrated?
Ans: Mass of an atom is concentrated in nucleus.
Ques 9: Name two elements with same number of protons and neutrons?
Ans: Carbon (Protons = Neutrons = 6)
Oxygen (Protons = Neutrons = 8)
Ques 10: Draw the atomic structure of sodium atom.
Ques 11: Name the isotope used for the treatment of cancer.
Ans: Isotope of cobalt.
Ques 12: AZX What does this symbol represent?
Ans: X —> Symbol of element
A —> Mass number
Z —> Atomic number
Ques 13: Can the value of ‘Z’ be same for two different atoms?
Ans: No, (Z = atomic number), two different atoms cannot have same atomic number.
Ques 14: Can the value of A’ be same for two different atoms?
Ans: Yes, it can be e.g. Ca and Ar has A-40 (i.e., mass number).
The helium atom is having 2 electrons, 2 protons and 2 neutrons.
(ii) Argon is and atom with L and M shell filled —->K L M- 2, 8, 8
Ques 4: What is an octate? Why would atoms want to complete their octate?
Ans: When the outermost shell of an atom i.e., L, M or N are completely filled with 8 electrons in the shell, it is said an octate. Atoms would want to complete their octate because they want to become stable.
Ques 5: Find the valency of 147N and 3517Cl.
Ans: The atomic number of nitrogen = 7, No. of protons = 7, No. of electrons = 7
Electronic configuration = K L M =2 5 –
Valency = 3
Because either it will gain three electrons or share 3 electrons to complete its octate.
The atomic number of chlorine = 17, p = 17, e=17
Electronic configuration = K L M= 2 8 7
Valency = 1
Because it will gain 1 electron to complete its octate.
Ques 6: Pick up the isotopes among the following and state reason.
Ans: The isotopes are 3517X and 3717X as both the atoms show the same atomic number but a different mass number.
Ques 7: Pick up atoms that have same number of neutrons from the following:
Ques 8: What are nucleons? What is the name given to those atoms which have same number of nucleons in it?
Ans: Protons and neutrons present in the nucleus are called nucleons Isobaric elements have same number of nucleons in it.
|Element||Protons||Neutrons||(Protons + Neutrons)|
Ques 9: Give the difference between three sub-atomic particles.
Ans: Three sub-atomic particles are electron, proton and neutron
Ques 10. Give the names of three atomic species of hydrogen.
Ans: Three atomic species of hydrogen are: Hydrogen, Deuterium, Tritum
Ques 11: Atomic Mass exists as a whole number, why do we write the atomic mass of chlorine as 35.5 u.
Ans: Chlorine has two isotopes and the mass of an atom is taken as the average mass of all the naturally occurring atoms of that element.
This is obtained by knowing the percentage of each isotopic from and then the average mass is calculated Cl = 35 - 75% and Cl = 37 - 25%
Ques 12: Give the difference between isotopes, and isobars.
|Are atoms of same element.||Are atoms of different element|
|Have same atomic number||Have different atomic number|
|Have different mass number||Have same mass number|
|Number of protons and electrons are same in these atoms.||Number of protons and electrons are not same in these atoms.|
Ques 13: Number of protons and electrons are same in an atom. Then why is it wrong to say that atomic number of an atom is equal to its number of electrons.
Ans: Atomic number ≠ Number of electrons, although number of protons = number of electrons because the electron’s number can change in an atom by loss, or gain of it. But the proton’s number remains constant (as it does not take part in loss or gain).
Ques 14: An atom is electrically neutral, on loss or gain of electrons why does it become charged?
Ans: An atom is electrically neutral because of a same number of protons and electrons. But it becomes charged, to become a stable atom, loses or gains electrons. Hence,
Number of protons ≠ Number of electrons
If it loses electrons p > e; hence +ve charge is obtained.
If it gains electrons e > p; hence -ve charge is obtained.
Ques 15: What is valency? Explain different types of valencies.
Ans: The combining capacity of an atom is called its valency. There are 2 types of valencies.
|When an atom share electrons, they have combined capacity.||When an atom loses or gains electrons|
Some atoms also show zero valencies when their outermost shell is completely filled.
Ques 16: With the help of activity in daily life, how can you prove that atoms are divisible.
• Take a scale, rub it on hair, try to attract a small bit of paper.
• Now divide the bit of paper further into smaller pieces.
• Again bring the charged scale near to these pieces of papers.
• You will observe that the bits of paper still get attracted.
Conclusion: This activity shows that the atom contains charges and these charges are opposite in nature which shows the attraction. Hence here scale and paper are oppositely charged and hence attract each other. Also, every atom has at least one sub-atomic particle.
Ques 17: In the structure of an atom why are protons present in the centre and are not pulled outside by the electrons as both are oppositely charged with the same unit of charge?
Ans: Protons are heavy with a mass 1 unit and hence are concentrated in the centre of the atom. The mass of electrons is negligible i.e.1/1800 times less than that of protons. Hence are not able to attract the protons and pull them out of the nucleus, although their charge is of the same value.
Ques 18: According to you, among the structure of atom studied which model is correct and why?
Ans: Bohr’s model of an atom is the best model and is correct because it gives the explanation of nucleons (protons and neutrons) in the centre and how electrons revolve around the nucleons in their discrete, special orbits, so electrons don’t loose/radiate energy and remain bonded in their shell.
(1) Most of the α-particles passed straight through the foil.
(2) Some of the α-particles were deflected by small angles by the foil.
(3) One out of every 12000 particles rebounded.
The conclusion from observation:
(1) Most of the space inside the foil is empty.
(2) Positive charge of the atom occupies very little space.
(3) Mass of the atom is concentrated in the centre with all positive charge concentrated in a small volume within the atom.
Ques 4: Establish the relationship between atomic number, mass number, isotopes, isobars and valency of an atom.
Ans: Atomic number — Gives the number of protons (Z)
Mass number — Gives the number of protons and neutrons (A)
Isotopes — When atoms of the same element have the same number of protons (Z) but different number of neutrons (s) such atoms are called isotopes.
Isobars — When an atom of different elements have the same mass number (A) but different atomic number (Z) such atoms are called isobars.
Valency — It is the combining capacity of an atom.
|1. What is the structure of an atom?|
|2. What are the subatomic particles in an atom?|
|3. How are protons, neutrons, and electrons arranged in an atom?|
|4. What is the role of protons, neutrons, and electrons in an atom?|
|5. How does the structure of an atom relate to its properties?|