Question 1

Question 11Draw the atomic diagrams of the following elements showing the distribution of - protons, neutrons & the electrons in the various shells of the atoms.(a) Carbon - 126C(b) Oxygen - 168O(c) Phosphorus - 3115P(d) Argon - 4018Ar(e) Calcium - 4020Ca[The upper number represents the - mass number & the lower number the - atomic number e.g. calcium - mass number = 40, atomic number = 20]

Accepted Answer

(a) Carbon - 126C(b) Oxygen - 168O(c) Phosphorus - 3115P(d) Argon - 4018Ar(e) Calcium - 4020Ca

Question 2

Question 4cThe subatomic particle with positive charge isprotonneutronelectronnucleon

Accepted Answer

protonReason — A proton is a positively charged particle present in the nucleus of an atom.

Question 3

Question 4dIf the atomic number of an atom is 17 and mass number is 35, then number of neutrons will be35171852

Accepted Answer

18Reason — Number of neutrons = Mass number - Atomic number = 35-17 = 18.So, number of neutrons = 18.

Question 4

Question 4eThe number of electrons in an atom is equal to the number ofprotons in a neutral atomneutrons in a neutral atomnucleons in a neutral atomnone of the above

Accepted Answer

protons in a neutral atomReason — An electrically neutral atom has an equal number of electrons and protons.

Question 5

Question 4fThe sum of number of protons and number of neutrons present in the nucleus of an atom is called itsmass numberatomic numbernumber of electronsall of the above

Accepted Answer

mass numberReason — The sum of number of protons and number of neutrons present in the nucleus of an atom is called the mass number of that element.

Question 6

Question 5Name three fundamental particles of an atom. Give the symbol with charge on each particle.

Accepted Answer

The three fundamental particles of an atom are:Electrons — An electron is negatively charged particle denoted by the symbol -1e0.Protons — A proton is positively charged particle denoted by the symbol +1p1.Neutrons — A neutron is neutral charged particle denoted by symbol 0n1.

Question 7

Question 6Define the following terms:(a) Atomic number(b) Mass number(c) Nucleons(d) Valence shell

Accepted Answer

(a) The number of protons present in the nucleus of the atom of an element is called its atomic number.(b) The sum of the number of protons and the number of neutrons present in the nucleus of the atom of an element is called the mass number of that element.(c) The protons and neutrons are collectively called as nucleons.(d) The outermost shell of an atom is known as its valence shell or valence orbit.

Question 8

Question 7Mention briefly the salient features of Dalton's atomic theory (five points).

Accepted Answer

The salient features of Dalton's atomic theory are:Matter consists of very small and indivisible particles called atoms.Atoms can neither be created nor be destroyed.Atoms of an element combine in small numbers to form molecules of that element.Atoms of an element combine with the atoms of another element in a simple whole number ratio to form molecules of a compound.Atoms are the smallest unit of matter that take part in chemical reactions during which only rearrangement of atoms takes place.

Question 9

Question 8(a) What are the two main features of Rutherford's atomic model?(b) State its one drawback.

Accepted Answer

(a) The two main features of Rutherford's atomic model are:An atom consists of mainly two parts : the centrally located nucleus and the outer circular orbits.The nucleus is positively charged mass and the entire mass of the atom is concentrated on it. The size of the nucleus is very small and it is the densest part of the atom. Electrons revolve around the nucleus in circular orbits called shells. An atom is electrically neutral i.e., number of protons is equal to number of electrons.(b) Rutherford could not explain the structural stability of an atom.

Question 10

Question 9What are the observations of the experiment done by Rutherford in order to determine the structure of an atom?

Accepted Answer

In his experiment, Rutherford bombarded a thin sheet of gold (of 0.00004 cm thickness) with fast-moving alpha particles in an evacuated chamber. He made the following observations from his experiment:Most of the alpha particles passed straight through the foil without any deflection from their path.A small fraction of them were deflected from their original path by small angles.Only a few particles bounced back.

Question 11

Question 10State the mass number, the atomic number, number of neutrons and electronic configuration of the following atoms.(a) 12C6(b) 16O8(c) 19F9(d) 20Ne10(e) 27Al13(f) 35Cl17Also, draw atomic diagrams for each of them.

Accepted Answer

(a) 12C6Atomic number: 6Mass number: 12Number of neutrons: 12 - 6 = 6Electronic configuration: 2, 4Atomic diagram:(b) 16O8Atomic number: 8Mass number: 16Number of neutrons: 16 - 8 = 8Electronic configuration: 2, 6Atomic diagram:(c) 19F9Atomic number: 9Mass number: 19Number of neutrons: 19 - 9 = 10Electronic configuration: 2, 7Atomic diagram:(d) 20Ne10Atomic number: 10Mass number: 20Number of neutrons: 20 - 10 = 10Electronic configuration: 2,8Atomic diagram:(e) 27Al13Atomic number: 13Mass number: 27Number of neutrons: 27 - 13 = 14Electronic configuration: 2, 8, 3Atomic diagram:(f) 35Cl17Atomic number: 17Mass number: 35Number of neutrons: 35 - 17 = 18Electronic configuration: 2, 8, 7Atomic diagram:

Question 12

Question 11What is variable valency? Name two elements having variable valency and state their valencies.

Accepted Answer

Some elements exhibit more than one valency and they are said to have variable valency.Examples: Iron and copper.MetalRadicalsValencyIron (Fe)Ferrous, Ferric2, 3Copper (Cu)Cuprous, Cupric1, 2

Question 13

Question 12The atomic number and the mass number of sodium are 11 and 23 respectively. What information is conveyed by this statement?

Accepted Answer

Atomic number of sodium is 11 means the number of protons present in the nucleus of sodium atom is 11 and the number of electrons present is 11. Mass number of sodium is 23 means the number of protons + number of neutrons is 23. So number of neutrons present is 12.

Question 14

Question 13Draw the diagrams representing the atomic structures of the following:(a) Nitrogen(b) Neon

Accepted Answer

(a) Atomic structure diagram of Nitrogen is given below:(b) Atomic structure diagram of Neon is given below:

Question 15

Question 14Explain the rule with example according to which electrons are filled in various energy levels.

Accepted Answer

Neil Bohr and Charles Bury proposed a scheme for distribution of electrons in different shells of an atom based on the formula 2n2, where n denotes the number of shell.The following rules are followed for writing the number of electrons in different energy levels or shells:The maximum number of electrons in each shell or orbit is determined by the formula 2n2, where n is the number of shell.K shell, n=1, no. of electrons = 2 x 12 = 2L shell, n=2, no. of electrons = 2 x 22 = 8M shell, n=3, no. of electrons = 2 x 32 = 18Electrons are not accommodated in a given shell, unless the inner shells are filled. Shells are filled in step-wise manner.If the atom has only one shell, the outermost shell must have 2 electrons to achieve stable electronic configuration. This is called the duplet rule. If the atom has more than one shell, then its outermost shell must have 8 electrons to achieve stable electronic configuration. This is called the octet rule.Example: Potassium has 19 electrons. The first shell will take 2 electrons, second shell will take 8 electrons. Remaining 9 electrons should be taken by third shell but according to octet rule, the outermost shell should not accommodate more than 8 electrons. So third shell take 8 electrons and remaining 1 electron will go to fourth shell. So electronic configuration of potassium is:KLMN2881\begin{matrix} 	ext{K} & 	ext{L} & 	ext{M} & 	ext{N} \ 2 & 8 & 8 & 1 \end{matrix}K2​L8​M8​N1​

Question 16

Question 15The atom of an element is made up of 4 protons, 5 neutrons and 4 electrons. What is its atomic number and mass number?

Accepted Answer

Atomic number = number of protons = 4.Mass number = number of protons + number of neutrons = 4 + 5 = 9.

Question 17

Question 16(a) What are the two main parts of which an atom is made of?(b) Where is the nucleus of an atom situated?(c) What are orbits or shells of an atom?

Accepted Answer

(a) An atom is made of:The nucleusThe orbits or the shells present in the empty space that surrounds the nucleus.(b) The nucleus is present in the central part of an atom.(c) Orbits or shells are the imaginary paths traced by the electrons in the empty space surrounding the nucleus.

Question 18

Question 17What are isotopes? How does the existence of isotopes contradict Dalton's atomic theory?

Accepted Answer

Isotopes are the atoms of the same element with the same atomic number but a different mass number due to the difference in the number of neutrons in their nucleus.According to Dalton's theory, atoms of an element are identical in all respects like size, mass, density, chemical properties. But isotopes of an element have atoms that have same atomic number i.e. same number of protons and electrons but different mass number i.e. number of neutrons are different. So isotopes differ from each other in their physical properties like density, melting point, boiling point, etc. This is a contradiction to Dalton's atomic theory.

Question 19

Question 18Complete the table below by identifying A, B, C, D, E and F.ElementSymbolNumber of protonsNumber of neutronsNumber of electronsFluorine9F199ABAluminiumCD1413Potassium19K39EF19

Accepted Answer

A → 10B → 9C → 13Al27D → 13E → 19F → 20Completed table is shown below:ElementSymbolNumber of protonsNumber of neutronsNumber of electronsFluorine9F199109Aluminium13Al27131413Potassium19K39192019

Question 20

Question 3The diagram represents an isotope of hydrogen [H]. Answer the following:Are isotopes atoms of the same element or different elements.Do isotopes have the same atomic number or the same mass number.If an isotope of 'H' has mass no. = 2, how many electrons does it have.If an isotope of 'H' has mass no. = 3, how many neutrons does it have.Which sub-atomic particles in the 3 isotopes of 'H' are the same.

Accepted Answer

Isotopes are atoms of the same element.Isotopes have same atomic number.Number of electrons in an isotope of 'H' having mass no. = 2 is 1 as its atomic number is 1.Number of neutrons in an isotope of 'H' having mass no. [A] = 3 is 2, because, atomic number [Z] is 1 so number of protons = number of electrons = 1 and number of neutrons [n] = A - Z = 3 - 1 = 2.Number of electrons and protons are same in the 3 isotopes of 'H' as atomic number is the same.

Atomic Structure

Arrangement of electrons

Exercise

Objective Type Questions

Sub-atomic particles