Atomic Structure

It can be seen that the third pair has atoms with same number of neutrons i.e. the two atoms are isotones. But, none other pair has isotenes.

Isotope is defined as the elements having similar mass number. And we know that

Mass Number = Total no. Of Protons+ Total no. of Neutrons

Thus, if mass no. is same then the no. of neutrons must be same.

Nucleons are referred to the protons and the neutrons.

Atomic number = Total no. of electrons = 35

Now, No. of electrons = No. of Protons = 35

And, Mass Number = Protons + Neutrons = 80

No. of neutrons = Mass no. – Protons

= 80 – 35 = 45

No. of electrons in Potassium = 19

No. of electrons in K-shell = 2

L-shell = 8

M-shell = 8

N-shell = 1

Thus, the Volume of oxygen used is 40 cm³

i) 0.398g metal oxide contains 0.318g of metal.

Therefore, amount of oxygen combining with

0.318g metal oxide I = 0.398-0.318 = 0.080g

ii) 0.716g metal oxide contains 0.636g of metal.

Therefore, amount of oxygen combining with

0.318g metal oxide I = 0.716-0.636 = 0.080g

Thus, for fixed mass of oxygen (0.080g), the metal forma oxides in the ratio = 0.318:0.636 = 1:2

Since, it is a simple ratio therefore the above data agrees with the law of multiple proportion.

Given:

Charge of proton = + 1.60 × 10⁻¹⁹ C

And, = 9.58 × 10⁷ C kg⁻¹

Thus, the mass of proton is

From theGold foil experiment, Rutherford and his team observed that:

● Most of the fast moving α-particles passed straight through the gold foil.

● Some α particles were deflected by small angles and a few by large angles.

● Surprisingly very few α particles completely rebounded.

Thus the conclusions made were:

● Atom has a very small nucleus at the centre.

● There is large empty space around the nucleus.

● Entire mass of an atom is concentrated in a very small positively charged region which is called the nucleus.

● Electrons are distributed in the vacant space around the nucleus.

● The electrons move in circular paths around the nucleus.

The main postulates of Bohr’s atomic model are:

● In atoms, electrons revolve around the nucleus in certain special or permissible orbits known as orbits or shells or energy levels.

● While revolving in these orbits the electrons do not radiate energy.

● The circular orbits are numbered as 1, 2, 3, 4, … or named as K, L, M, N, shells. These numbers are referred to as principal quantum numbers (n).

● K shell (n = 1) is closest to the nucleus and is associated with lowest energy. L, M, N, …. etc are the next higher energy levels. As the distance from the nucleus increases the energy of the shells also increases.

● The energy of each orbit or shell is a fixed quantity and the energy is quantized.

● As the distance from the nucleus increases, the size of the orbits also increases.

● Maximum number of electrons that can be accommodated in an energy level is given by 2n² where n is the principal quantum number of the orbit.

● When an electron absorbs energy, it jumps from lower energy level to higher energy level.

● When an electron returns from higher energy level to lower energy level, it gives off energy.

Gay Lussac’s law of combining volumes:

This law states that when gases react, they do so in volumes which bear a simple ratio to one another, and to the volume of the product(s) formed if gaseous, provided the temperature and pressure remain constant.

The law explains experimental facts about how gaseous atoms combine.

Example:

For the reaction: N_2(g) + 3H_2(g)→ 2NH_3(g)

1 vol. 3 vols. 2 vols.

1 volume of nitrogen combines with 3 volumes of hydrogen to form 2 volumes of ammonia.

Thus, the ratio is 1:3:2.

This satisfies the Gay Lussac’s law of combining volumes.

1. a) and d) Electrons

2. d) Neutrons

3. d) Protons

Figure1:

1. Valence electron: 4

2. Valency: 4

3. Atomic Number: 6

4. Mass number: 12

5. Electronic configuration: 2, 4

Figure2:

1. Valence electron: 2

2. Valency: 2

3. Atomic Number: 12

4. Mass number: 24

5. Electronic configuration: 2, 8, 2

Figure3:

1. Valence electron: 7

2. Valency: 1

3. Atomic Number: 17

4. Mass number: 35

5. Electronic configuration: 2, 8, 7

Figure4:

1. Valence electron: 2

2. Valency: 2

3. Atomic Number: 20

4. Mass number: 40

5. Electronic configuration: 2, 8, 8, 2

Figure5:

1. Valence electron: 1

2. Valency: 1

3. Atomic Number: 19

4. Mass number: 39

5. Electronic configuration: 2, 8, 8, 1

Figure6:

1. Valence electron: 3

2. Valency: 3

3. Atomic Number: 13

4. Mass number: 27

5. Electronic configuration: 2, 8, 3

c) 11, 12

(Since, the protons and neutrons remains same)

True

Yes, the electrons revolve around the nucleus in fixed orbits.

False

Isotopes of elements have different mass numbers.

False

Electrons have negligible mass but is has a charge of 1.602 x 10^-19 Coulombs.

True

Since, as we go higher the energy starts increasing. Thus higher the orbit higher will be the energy and lower the orbit lower will be the energy.

False

The no. of electrons in L shell is 8.

Since, No. of electrons = 2n² = 2(2)² = 2x4 = 8

Isobars

2n²

iodine-131

4

0

Since, argon is a noble gas thus its valency is zero.

*Deuterium is an isotope of Hydrogen

Rearranging in the increasing order of atomic number:

1. Helium

2. Boron

3. Oxygen

4. Fluorine

5. Neon

6. Sodium

7. Magnesium

8. Silicon

9. Sulphur

10. Calcium

Down

1. Alpha

2. Hydrogen

3. Argon

4. Valence

5. Carbon

6. Chadwick

Across:

1. Valence

2. Lone Pair

3. Hydrogen

4. Rutherford

● Box-1: Law Of Multiple Proportions:

This law states that when two elements combine with each other to form more than one compound, the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.

● Box-2: Law of Conservation of Mass:

This law states that the mass in an isolated system is neither created nor destroyed by chemical reactions or physical transformations.

According to the law of conservation of mass, the total mass of the reaction in a chemical reaction must equal the mass of the reactants.

● Box-3: Law of constant Proportions:

The law of constant composition says that, in any particular chemical compound, all samples of that compound will be made up of the same elements in the same proportion or ratio.

● Box-4: Law of Reciprocal proportions:

This law states that if two different elements combine separately with the same weight of a third element, the ratio of the masses in which they do so are either the same or a simple multiple of the mass ratio in which they combine.

● Box-5: Gay Lussac’s Law of Gaseous volumes:

This law states that the ratio between the volumes of the reactant gases and the gaseous products can be expressed in simple whole numbers. 2 molecules of hydrogen + 1 molecule of oxygen = 2 molecules of water.

Berilium (atomic number: 4)

Electronic configuration of K⁺:

K-shell: 2

L-shell: 8

M-shell: 8

(Since one electron is lost thus the electronic configuration will be like this)

Electronic configuration of Cl^-:

K-shell: 2

L-shell: 8

M-shell: 8

(Since one electron is added thus the electronic configuration will be like this)

Charge:

The electronic charge of the proton and the electron both are same. Only there is a change on sign.

Since proton has a positive charge thus its charge is +1.6 × 10^-19 C

Whereas electron has negative charge so the charge of electron is -1.6 × 10^-19 C.

Mass:

The proton is much heavier in weight whereas electrons have negligible weight.

The weight of proton is 1.67 × 10^-24 g whereas the mass of the electron is 9.31 × 10^-28 g.

We know that maximum no of electrons in:

K-shell = 2

L-shell = 8

M-shell = 18

Therefore; total no. of electrons = 2+8+18 = 28.

Ca²⁺ means that calcium has lost 2 electrons.

Now; atomic number of Ca = 20

Since, it has lost 2 electrons, thus the no of electrons left are = 18

Thus, atomic configuration of Ca²⁺ = 2, 8, 8

This shows that the Ca²⁺ has a completely filled outer shell.

Law of Multiple Proportions:

This law states that when two elements combine with each other to form more than one compound, the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.

Uranium235: This isotope of uranium is used as fuel in nuclear reactor.

Cobalt60: This isotope of cobalt is used in treatment of cancer.

Iodine131: This isotope of iodine is used in treatment of goitre.

Carbon14: This isotope of carbon is used in Carbon dating (that is to find the age of plants and animals).

Isotone is defined as two or more atoms having the same number of neutrons.

Example: chlorine-37 and potassium-39 are isotones, because the nucleus of this species of chlorine consists of 17 protons and 20 neutrons, whereas the nucleus of this species of potassium contains 19 protons and 20 neutrons.

Structure of oxygen atom:

Structure of sulphur atom:

i) Given,

Atomic Number = 3

Mass Number = 7

Therefore,

No. of electrons = atomic number = no. of protons = 3

And,

Mass Number = no. of protons+ no. of neutrons = 7

Thus, no. of neutrons = 4

ii) Given,

Atomic Number = 92

Mass Number = 238

Therefore,

No. of electrons = atomic number = no. of protons = 92

And,

Mass Number = no. of protons+ no. of neutrons = 238

Thus, no. of neutrons = 238-92 = 146