Structure Of Atom

The subatomic particle is not present in an ordinary hydrogen atom is neutron.

The scientists who described the arrangement of electrons in an atom was J.J. Thomson

The maximum number of electrons which can be accommodated in the K shell of an atom is 2.

The maximum number of electrons which can be accommodated in the L shell of an atom is 8.

The maximum number of electrons an M shell of the atom can accommodate is 18.

The maximum number of electrons that can go into the N shell of an atom is 32.

(a) The maximum number of electrons which can be accommodated in the innermost shell of an atom is 2.

(b) The maximum number of electrons which can be accommodated in the outermost shell of an atom is 8.

The three subatomic particles present in an atom are electron, proton and neutron.

The negatively charged particle present in the atoms of all the elements is electron.

J.J. Thomson was the scientist who discovered electrons.

e^-, p⁺, n are the usual symbol for electron proton and neutron respectively.

(a) False, this statement is not true.

(b) True. Yes, the cathode rays obtained from all the gases consist of negatively charged particles called electrons.

(c) False, The anode rays obtained from all the gases consist of positively charged particles called protons is not a true statement.

The central part of an atom where protons and neutrons are held together is nucleus.

The various letters used by Bohr to represent electron shells in an atom are K, L, M and N.

The particles which actually determine the mass of an atom is proton.

The positively charged particle present in the atoms of all the elements are protons.

The electronic configuration of a hydrogen atom is 1.

A proton is 1840 times heavier than an electron.

The gas which produces anode rays consisting of protons in the discharge tube experiment was hydrogen.

The part of an atom was discovered by Rutherford’s alpha particle scattering experiment was nucleus.

The positive charge on the nucleus of an atom is due to the presence of protons.

(i) In neon the number of electrons present in the outermost shell of the atom is 8.

(ii) Chlorine the number of electrons present in the outermost shell of the atom is 7.

(a) 8 electrons can be accommodated in L shell.

(b) 32 electrons can be accommodated in N shell.

(a) the shell of an atom which can accommodate a maximum of 2 electrons is L.

(b) the shell of an atom which can accommodate a maximum of 18 electrons is M.

(i) neutrons by Chadwick.

(ii) electrons by Thomson.

(iii) protons by Goldstein.

(a) +1 represent protons.

(b) -1 represent electron.

(c) o represents neutrons.

(a) The number of protons in the nucleus of an atom is called its atomic no.

(b) The total number of protons and neutrons in the nucleus of an atom is called its mass no. .

(c) An atom has atomic mass number 23 and atomic number 11. The atom has 11 Electrons.

(d) An atom of an element has 11 protons, 11 electrons and 12 neutrons. The atomic mass of the atom is 23.

(e) If the nucleus of an atom has atomic number 17, mass number 37 abd there are 17 electrons outside the nucleus, the number of neutrons in it is 20.

(f) Almost all the mass of an atom is concentrated in a small region of space called the nucleus.

(g) Cathode rays are a beam of fast moving electrons.

(h) The anode rays obtained form hydrogen gas consist of particles called protons.

(i) The maximum number of electrons that can be accommodated in L shell are 8.

(j) The maximum number of electrons that can go into the M shell is 18

(k) The subatomic particle not present in a hydrogen atom is neutron.

(l) The electron has negative. charge, the proton has positive charge, and the neutron has no charge.

(a) 8 is the number of valence electrons in sodium ion, Na⁺ has the electronic configuration of 2, 8.

(b) 8 is the number of valence electrons in oxide ion, as O^2- have the electronic configuration of 2, 8.

(i) Atom A have 82 protons.

(ii) Atom B have 83 protons.

(iii) Both the atoms A and B are not the isotopes of same element.

, this pair is isotopes because they have same atomic number.

(i) The subscripts (lower figures) represents the atomic number and the superscripts (upper figures) represents the mass number.

(ii) The factor is responsible for the change in the superscripts 16, 17 and 18, though the element is the same number of neutrons.

(iii) The usual name for such atoms of an element is isotopes.

(iv) The nuclear composition of is that it have 8 protons and 10 neutrons

A and B are the example of isobars. Because isobars have same number of nucleons but they have different numbers of protons.

The mass numbers of A and B is 40 the relation between the two species is that, they are isobars and the element or elements they represent are Argon and Calcium respectively.

, is a pair of isobar. The reason behind I, they both have same number of neutrons.

A pair of isotopes from the above particles is A and D. This is so, because both the isotopes have same number of protons but they have different number of neutrons.

(i) The mass number of X is (8+8) = 16.

(ii) The mass number of Y is (8+9) = 17.

(iii) The relation between X and Y is, both are isotopes.

(iv) Both the element X and Y represents the oxygen.

A negatively charged particle found in the atoms off all elements is known as electrons.

1/1840 u is the relative mass of an electron.

An electron carries a charge of -1.

9 × 10^-28 Kg is the absolute mass of electron.

In Rutherford's scattering experiment the deflection of fast moving particles through small and large angles is the evidence for the presence of nucleus in an atom.

Important information furnished about nucleus in Rutherford's alpha- particle scattering experiment is:

1) A positively charged particle in an atom is nuleus.

2) According to the information from the experiment nucleus of an atom is very hard and dense.

3) As compared to the size of an atom as a whole nucleus is very small in size.

The most of the space in an atom is empty this can be seen from the Rutherford's alpha- particle scattering experiment as most of the alpha- particles passed straight through the gold foil without any deflection.

AN atom is neutral inspite of the of the presence of the charged particles in it because of the presence of nutrons.

The nuclear particles is present in the same fixed number in the atoms of any particular element is proton.

The characteristic of any particular is its atomic no.

A positively charged particle in atom of any particular element is known as proton.

1u is the relative mass of the prton.

+1 C is the relative charge of the protons.

1.6 × 10^-27 Kg is the absolute mass of proton. And 1.6 × 10^-19 C is the absolute charge on the proton.

A proton differ from an electron:

1) Protons have positive charge on it while electron have negative charge on it.

2) Electrons are lighter then protons.

The two observations which shows that atom is not indivisible are:

1) the stream of cathode rays in the gas discharge tube shows the presence of negatively charged subatomic particles called electrons from the J.J. Thomson's experiment.

2) the faint red glow in the gas discharge tube shows the presence of positively charged subatomic particles called protons this is known from Goldstein's experiment.

(i) The presence of negatively charged electrons in all the atoms is told by the cathode ray formation.

(ii) The presence of positively charged protons in all the atoms is told by the formation of anode rays.

In the various shell of the atom there are arrangements of electrons which is known as electronic configuration. Oxygen whose atomic number is 8 have the E.C 2,6

At the center of the atom a small positively charged particle is present this is known as nucleus. The nucleus is positively charged particle.

The scientist who discovered the nucleus of atom is Rutherford.

The particle used by Rutherford in his experiment on the discovery of nucleus is known as alpha particle. +2 is the charge of the alpha particle.

(a) In each atom of an element the no. of electron is 13.

(b) These electrons distributed in the various energy levels like K-2, L-8, M-3. Its electronic configuration is 2, 8, 3.

The atomic no. of the element is 18, so the adjustment of electrons as per in K, L, M shell is like 2, 8, 8 respectively. The outermost shell of this element is completely filled.

A neutral particle found in the nucleus of an atom is known as neutrons. Neutron has no charge on it with a relative mass of 1u.

The relative mass of electron is 1/1840 u, and the relative mass of proton and the neutron is 1 u each.

A positively charged particle found in the atoms of all the elements is known as proton. Whereas neutron is found in the nucleus of an atom and is neutral in behavior.

Electron has relative mass of 1/1840 u and it has a charge of -1 u on it. Whereas proton has relative mass of 1u and it also has +1 u charge over it.

Proton has relative mass of 1u and it has +1 u charge over it. Whereas neutron also have relative mass of 1u but it do not have any charge over it.

The electron differ from a neutron because, electron has relative charge of -1 u whereas neutron has no relative charge.

Also, electron has relative mass of 1/1840 u and neutron has relative mass of 1 u.

In an atom neutrons are in the center of the atom. The electrons revolves in the outermost orbit of the energy shell, whereas the protons are positioned in between the neutrons and electrons.

Cathode rays are the stream of particles coming from the cathode. Cathode rays are negatively charged in nature.

when we pass very high voltage electricity through a gas at low pressure in a discharge tube, the stream of particles are given out by cathode which is known as cathode ray.

All the atoms contain negatively charged particles called electrons is the conclusion obtained from the fact that all the gases form cathode rays.

Thomson’s model of the atom describes that an atom consists of a sphere of positive charge with negatively charged electrons embedded in it. And also states that the positive and negative charges in an atom are equal in magnitude. The subatomic particle was not present in Thomson’s model of the atom was neutron.

Given the mass no. and the no. of electrons are 18 and 7 respectively. Then the no. of protons and neutrons are 7 and 11 respectively.

The Rutherford’s model of an atom can be described by many statements some of then are:-

1) An atom consists of positively charged, dense and very small nucleus containing all the protons and neutrons. Almost all the mass of atom is concentrated in the nucleus.

2) The electrons are revolving at very high speed round the nucleus in fixed circular orbits. And it surround the nucleus.

3) The electrostatic attraction between the positively charged nucleus and negatively charged electrons keep the atom held together.

4) The atom has mostly empty space.

Give,

The mass number of an element is 23, no. of electrons are 11.

Then the no. of protons are 11. And the no. of neutrons are (23-11) = 12.

The atomic no. of the element is 11.

The Bohr’s model of the atom is described by several statements:-

1) Three particles collectively makes the atom and these are electrons, protons and neutrons.

2) The protons and neutrons are located in the small nucleus at the center of atom.

3) Electrons revolve round the nucleus in fixed circular orbits.

4) For every shell the maximum no. of electrons are fixed. Any shell cannot exceed that value.

5) Each given shell is associated with fixed amount of energy.

6) There is no change in energy of electrons as long as they keep revolving in the same energy level, and the atom remains stable.

Give,

An element has an atomic number of 11

its mass number is 23.

E.C = 2, 8, 1.

The nuclear has 11 protons and 12 neutrons.

(i) The no. of protons in one atom of an element is known as atomic no.

(ii) The total no. of protons and neutrons present in one atom of an element is known as mass no.

The relation between the atomic number and mass number of an element is, Atomic no. + no. of Neutrons = Mass no.

If an element M has mass number 24 and atomic number 12 then no. of neutrons = (24-12) = 12.

Rutherford’s alpha particle scattering experiment led to the discovery of nucleus.

The correct electronic configuration of sodium is 2, 8, 1.

The particle not present in an ordinary hydrogen atom is neutron.

The subatomic particle called electron was discovered by J.J. Thomson.

Magnesium ion, Mg²⁺ has 10 electrons; so, its electronic configuration is 2, 8.

The correct electronic configuration of a chloride ion is 2, 8, 8.

Goldstein’s experiments which involved passing high voltage electricity through gases at very low pressure resulted in the discovery of proton.

The number of electrons in the atom of an element X is 15 and the number of neutrons is 16. The correct representation of an atom of this element is .

The ion of an element has 3 positive charges. The mass number of atom of this element is 27 and the number of neutrons is 14. The number of electrons in the ion are 10.

The first model of an atom was given by J.J. Thomson.

An atom has equal number of electrons and protons.

From the symbol <ιμγωιδτη=∀31∀ηειγητ=∀32∀σρχ=∀Χη−4_Στρυχτυρε−οφ−Ατομ−1_φιλεσ/ιμαγε009.πνγ∀>, state

(i) mass number of phosphorus is 31

(ii) atomic number of phosphorus is 15.

(iii) electron configuration of phosphorus is 2, 8, 5.

(a) The electronic configuration of element X is 2, 8, 7.

(b) The atomic number of element X is 17.

(c) Element X is a non-metal.

(d) Anion will be formed by an atom of element X. The symbol of the ion formed will be X⁻.

(e) It should must be chlorine (Cl).

(a) The atomic number of element E is 3.

(b) Element E’s mass number is 7.

(c) The electronic configuration of the element E is 2, 1.

(d) As element E has 1 valence in its outer most shell, so metal. As it shows the tendency to give electron to attain the noble gas configuration.

(e) Cation will be formed by an atom of element E because it has 1 electron in the outer most orbit, which it can lose quickly to form a positively charged ion.

(f) The symbol of the ion formed by an atom of element E is E⁺.

(g) Element E could be Lithium.

(a) The figure 9 indicates mass number.

(b) The figure 4 indicates atomic number.

(c) The number of protons in atom X should be 4.

(d) The number of neutrons in atom X should be 5.

(e) The number of electrons in atom X is 4.

(f) In the outermost shell of an atom of element X there are 2 electrons.

(g) The symbol of ion formed by an element Z is Lithium (Li)

(a) The atomic number of the element Z is 18.

(b) Element Z is a non-metal.

(c) By an atom of element Z the ion formed will be anion. This is because it has completely filled shell due to which it can neither lose or gain electron.

(d) The outermost electron shell or the atom of this element is completely filled with electrons. It has its noble gas configuration.

(e) The name of the element is argon. And its symbol is Ar.

(f) The group of elements to which Z belongs is noble gas or can say inert gas.

The total number of electrons in a nitrogen atom is 7 so its E. C is 2, 5. And the no. of valance electron in it is 5.

The general name of the elements having 8 electrons in the valence shell of their atoms is noble gas.

The noble gas which has less than 8 electrons in the valence shell of its atom is helium. The atomic no. of helium is 2.

For the treatment of cancer radioactive isotopes is used.

A radioactive isotope which is used as a fuel in the reactors of nuclear power plants is Uranium-235.

The radioactive isotope which is used in the treatment of cancer is Cobalt-60.

To determine the activity of thyroid gland Iodine-131 is used as a radioactive isotopes.

To detect the leakage in underground oil pipelines, gas pipelines and water pipes we use radioactive isotopes in the industries.

The above given statement is not true.

Those atoms which contain the same number of protons and electrons but different number of neutrons are named as isotopes.

The relationship between an atom containing 11 protons, 11 electrons ad 11 neutrons, and another atom containing 11 protons, 11 electrons and 12 neurtrons is, they are isotopes in nature.

The pair of atoms such as are known as isotopes.

Those isotopes which have unstable nuclei and emit various types of radiations are named as radioactive isotopes.

(a) Magnesium has 3 valence electrons in the M shell.

(b) The valency of nitrogen in N₂ molecule is 3.

(c) Isotopes have different mass numbers because their nuclei contain different number of neutrons.

(d) Some boron atoms have mass number 10 and some have mass number 11. These boron atoms with different mass number are called isotopes.

(a) The nucleus of an atom has 5 protons and 6 neutrons then the atomic no. 5.

(b) The nucleus of an atom has 5 protons and 6 neutrons then the mass no. will be 6+5 = 11.

(c) The nucleus of an atom has 5 protons and 6 neutrons then the no. of electrons = 5.

(d) The nucleus of an atom has 5 protons and 6 neutrons then the no. of valance electrons, per atom = 3.

The electronic configuration of the element with atomic number 17 will be (2, 8, 7). The valency of the element will be 8 and the no. of valance electron will be (8-7) = 1.

(a) The atomic number of an element X is 16. The E.C can be given as (2, 8, 6).

(b) The atomic number of an element X is 16. The valency of X will be 8 and the no. of valance electron will be 2.

When atomic no. is 2 then the valency shown by A – 0

When atomic no. is 4 then the valency shown by B - 2

When atomic no. is 8 then the valency shown by C - 2

When atomic no. is 10 then the valency shown by D - 0

When atomic no. is 13 then the valency shown by E - 3

(a) As a fuel in the reactors of nuclear power plants for generating electricity we use Uranium-235.

(b) for the treatment of cancer we use Cobalt–60.

are not considered isotopes because they do not have same atomic number.

the reason for the different atomic masses of the isotopes of an element is, due to different number of neutrons in their nuclei.

The reason for the identical chemical properties of all the isotopes of an element is, all the isotopes of an element have identical atomic configuration containing same number of valence electrons.

For example: Cl-35 and Cl-37, show identical chemical properties as they have same no. of 7 valence electrons.

The reason for the slightly different physical properties of all the isotopes of an element is the slight difference in the masses of the element.

The atomic masses of many elements are in fractions and not whole numbers because of the existence of their isotopes having different masses.

Deuterium, Tritium and Protium are isotopes here and Argon and Calcium are isobars.

(i) These isotopes have almost identical chemical properties because of their identical electronic configuration containing the same no. of valence electrons.

(ii) They are electrically neutral all of them have 1 electron and 1 proton.

Atomic mass = ∑Mass no. × % of that isotope

The atoms of different elements having different atomic numbers but the same mass number (or same atomic mass) are known as isobars. Example of isobar is Cl, S etc.

sub atomic particles in H, D, and T can be given as:

H = 1 proton, 0 neutron and 1electron.

D = 1 proton, 1 neutrons and 1 electron.

T = 1 proton, 2 neutrons and 1 electron.

Given that the element has atomic number 7.

So its E.C = 2,5.

So, the valency of this element is 3. And the name of the given element is Nitrogen.

Valance electrons are the number of electrons present in the valance shell. In the outermost shell valance electrons are present.

An element having atomic number 13 have the electronic configuration 2, 8, 3. So the valance shell of the atom of this element have 3 electrons. The valance of this atom is M.

The atoms of the same element having the same atomic number but different mass numbers are known as isotopes. For example: the isotopes of chlorine are 35Cl17 and 37Cl17.

The basic similarity between a pair of isotopes is, both have same atomic number.

The basic difference between a pair of isotopes is, both have different mass number.

In the number of protons, neutrons and electrons are 17, 18, 17 respectively.

In the number of protons, neutrons and electrons are 17, 20, and 17 respectively.

Due to presence of extra neutrons in their nuclei some isotopes are unstable and emit various types of radiations. These isotopes are called radioactive isotopes.

The two examples of the radioactive isotopes are:

Carbon-14, and Arsenic-74.

The uses of radioactive isotopes are:

(1) For the treatment of cancer radioactive isotopes are use.

(2) As 'tracers' in medicine to detect the presence of tumors and blood clots in human body radioactive elements are used.

Given, Average atomic mass = 35.5 u

Let % amount of ³⁵Z₁₇ be y, then amount of ³⁷Z₁₇ is (100 - y).

So,

So, 35y + 3700 – 37y = 3550

Hence, y = 75

Thus, amount of ³⁵Z₁₇ is 75% and amount of ³⁷Z₁₇ is 25%

The valency of an element is defined as the capacity of an atom of an element to form chemical bonds. An element having atomic number 14 will show the valency 4.

The relation between the valency of an element and the number of valence electrons in its atoms is that, the valency of an element is either equal to the number of valence electrons in its atom or equal to the number of electrons required to complete eight electrons in the valence shell.

No. of electrons in an atom = valency of metal.

8 are the no. of valence electron in its atom = valency of non-metal.

For example- the valency of sodium metal is 1 where as the valency of chlorine non-metal is also 1.

X and Y are examples of isobars.

An atom can have only electron and proton but o neutron is the correct statement about the atoms of an element.

They have the same number of protons is correct regarding this species.

The radioactive isotope used in the treatment of cancer is cobalt – 60.

Elements having valency ‘one’ are either metals or non-metals.

The two oxygen atoms are isotopes is the correct reason for the two oxygen atoms have the same number of electrons but different number of neutrons.

Carbon do not exhibit electrovalency.

The number of valence electrons in a graphite atom is 4.

The element which cannot form a cation is C.

The number of valence electrons in a sulphide ion, S^2-, is 8.

The valency of element Z will be 1.

The element which cannot form an anion is most likely to be X.

The two species which can be termed isobars are (ii) and (iii).

The element which can exhibit covalency as well as electrovalency will be S.

The atomic number of an element X is 8 and that of element Y is 4. Both these elements can exhibit a valency of 2.

The isotopes of an element contain different number of neutrons but same number of protons.