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(a) Noble gases- H and P

(b) Halogens- G and O

(c) Alkali metals - A and I

(d) D and L have valency of 4

(e) I with atomic number 11.

(f) Cl has the least atomic size in period 3 with atomic number 17.

As we move down a group, the numbers of shells increases and hence the atomic size increases.

Therefore, Z will have the smallest atomic number followed by Y, while X will have the largest atomic number.

So the elements in order of increasing atomic number will be Z<Y<X.

Position in a group: X and Y

Position in a period: Y and X

Helium has the highest ionization energy of all the elements while cesium has the lowest ionization energy

Second period: Neon > Fluorine > Oxygen > Nitrogen > Carbon > Boron > Beryllium > Lithium

Third Period: Argon> Chlorine > Sulphur > Phosphorus > Silicon > Aluminum >Magnesium > Sodium

Electron affinity depends on:

(a) Atomic size

(b) Nuclear charge

(a) Electron affinity is the energy released when a neutral gaseous atom acquires an electron to form an anion.

(b) Second period: Lithium<Boron<Carbon<Oxygen<Fluorine Neon, Nitrogen and Beryllium do not follow the trend.

(a) (iv) Argon

(b) (iii) Calcium

(c) (iii) Helium

(a) Group 1since the valence electrons is 1

(b) With 4 shells T belong to period 4.

(c) Number of electrons = 2+8+8+1=19

(d) T needs to lose one electron to complete its octet hence its valency is 1

(e) Since it has one valence electron, it is a metal

Answer is Metals

Complete the following sentences choosing the correct word or words from those given in brackets at the end of each sentence:

(a) The properties of the elements are a periodic function of their atomic number (atomic number, mass number, reative atomic mass).

(b) Moving across a periods of the periodic table the elements show increasing non-metallic character (group, period, metallic, non-metallic).

(c) The elements at the bottom of a group would be expected to show more metallic character than the element at the top. (less, more).

(d) The similarities in the properties of a group of elements are because they have the same number of outer electrons (electronic configuration, number of outer electrons, atomic numbers).

Transition elements – Elements belonging to Group 3 to 12 are called transition elements. Transition elements consists of metals lying between strongly elctropositive metals on a left and least electropositive elements on the right. They all have similar properties. 

Inner transition elements: Inner transition elements are the elements belonging to Group 3 in 6th and 7th period. 

They form two series i.e. Lanthanide series and Actinide series. 

They consists of two Horizontal rows of metals at the bottom of the table. 

The gases of zero group (Noble gases) are unreactive because they have a stable electronic configuration. 

(a) The total number of electron shells in an atom determines the period to which the element belongs, and the valence electrons determine the group to which it will belong. So with the help of electronic configuration we can figure out the period and group number of an element.

Elements with one and two valence electrons belong to group 1 and 2 respectively, while to determine the group number of elements with 3 to 8 valence electrons, we add 10 to their valence electrons.

For example an element X has atomic number 15

Its configuration will be:

K shell has 2 electrons, L will have 8, and the remaining 5 will be placed in M shell

Since it has three shells it belongs to period 3 and with 5 valence electrons the element will be placed in five plus ten that is the 15th group

So with the help of electronic configuration we can figure out the period and group number of an element.

(b) Atomic number = Number of protons

Hence, number of protons in K atom = 19

Number of neutrons = Mass number − Atomic number

Hence, number of neutrons in K atom = 39−19 = 20

Number of electrons = Number of protons

Hence, number of electrons = 19

And electronic configuration of K atom = 2, 8, 8, 1

Since K atom has 4 shells, hence it belongs to fourth period.

With one valence electron, it belongs to group 1

Number of protons in P atom = 15

Number of neutrons in P atom = 31−15 = 16

Number of electrons in P atom = 15

And electronic configuration of P atom = 2, 8, 5

Since it has three shells, it belongs to period 3 and with 5 valence electrons Phosphorus is found in five plus ten that is 15th group.

Elements of group 1 and 2 also those in groups of 13 – 18 are called representative elements it belongs to metals, nonmetals, and metalloids.

Two demerits of Modern Periodic table are:

(a) Hydrogen resembles both the alkali metals and halogens, But it has been placed with the alkali metals.

(b) The lanthanides and actinides have not been placed in the main body of the table.

i. There are six elements between P and Q. 

ii. Newland law states that “When the elements are arranged in an increasing order of their atomic masses, the properties of the 8^th element are similar to the properties of the 1^st element. 

iii. The repetition in the properties of the element is just like the repetition of eighth note in an octave of music, so it is known as the Newland’s law of octaves.

i. (2, 7) 

 It is flourine 

 It is placed at 17^th group and period 2. 

 ii. (2, 8, 8) 

 It is Argon 

 It is placed at 18^th group and period 3. 

Nitrogen is placed at first position in 15 groups. Atomic number is N = 7
Electronic configuration is 1s², 2s², 2p³, so outer most electronic configuration is [2s², 2p³]

Inner transition elements from Cerium [Ce] to Lutecium [Lu] of period 6 are called lanthanides. Inner transition elements from Thorium (Th] to Lewrencium [Lr] of period 7 are called actinoids. Lanthanoids are also called rare earth. Actinoids are man-made artificial elements (except thorium and uranium).

(a) (Al)₂(SO4)₃

(b) Covalent bonding

(c) Same number of valence electrons

(d) Helium

(e) 8 

(f) Electron affinity

(g) The atomic size Decreases as we move from left to right across the periods, because the atomic number increases but the number of shells remains the same

(a) Neon

(b) Aluminum

(c) Phosphorus

(d) Calcium

(e) Carbon

The cation has smallest radius. The reason for the smaller size of cation are:

1. A cation is formed by loss of one or more electrons from the parent atom. Generally the whole of the outermost shell of electrons is removed so that the resulting cation is smaller in size.

2. Also, in the formation of cation, electrons are removed but the magnitude of nuclear charge remains the same i.e., same nuclear charge will work on less number of electrons. In other words, effective nuclear charge per electron increases and as a result, electrons are strongly attracted and pulled towards the nucleus. This causes decrease in size.

(a) Anion is formed by the gain of electrons. Thus the numbers of electrons are more than protons. The effective positive charge in the nucleus is less, so less inward pull is experienced. Hence the size expands. So the size of an atom is greater than the size of parent atom.

(b) Since Argon has stable octet configuration, so due to the inter- electronic repulsions the effect of nuclear pull over the valence shell electrons cannot be seen which results in the bigger size.

(c) Since size of Bromine is bigger than chlorine, so it becomes more difficult for Br atoms to attract electrons. Thus, Cl is more reactive than Br.

(i) Across a period, the chemical reactivity of elements first decreases and then increases.

(ii) Down the group, chemical reactivity increases as the tendency to lose electrons increases down the group

(i) The atomic size of an atom increases when we go down a group from top to bottom

(ii) It increases as we move from right to left in a period

Atomic size is the distance between the centre of the nucleus of an atom and its outermost shell.

It's measured in Angstrom and Picometre

(i) Electron affinity

(ii) Atomic size

(iii)Metallic character

(iv)Non-metallic character

(v) Ionization energy

Metals: Lithium, Beryllium, Sodium, Magnesium, Aluminium, Potassium, Calcium.

Non-metals: Hydrogen, Helium, Carbon, Nitrogen, Oxygen, Fluorine, Neon, Phosphorus, Sulphur, Chlorine, Argon.

(i) An atom is always bigger than cation since cation is formed by the loss of electrons; hence protons are more than electrons in a cation. So the electrons are strongly attracted by the nucleus and are pulled inward.

(ii) An anion is bigger than an atom since it is formed by gain of electrons and so the number of electrons are more than protons. The effective positive charge in the nucleus is less, so less inward pull is experienced. Hence the size expands.

(iii) An anion is bigger than an atom since it is formed by gain of electrons and so the number of electrons are more than protons. The effective positive charge in the nucleus is less, so less inward pull is experienced. Hence the size expands.

De-merits of Mendeleev’s periodic table are:

(i) Couldn’t explain position of Hydrogen.

(ii) Position of isotopes was not clear.

According to Mendeleev’s periodic law, the physical and chemical properties of elements are the periodic function of their atomic weights. Thus elements are grouped according to their atomic weight.

According to the Modern periodic law, the properties of the element and their compound are a periodic function of their atomic numbers. When element are placed according to atomic number, then similar electronic configuration are repeated after regular interval. Hence element are placed in periodic table according to increasing atomic.

(b) Atomic weight

Period no. = no. of shells, so n = 3

From the formula M2O3 its valency is 3.

Since it is a metal, its valence shell has 3 electrons.

So its electronic configuration is 2, 8, 3

Atomic number =13

Hence the metal is Aluminum with valency 3.

1. J

2.  R

3.  M

4. Y

5. 5

 6. T

 7. Ionic bond. Formula is A₂H.

Beryllium and magnesium will show similar chemical reactions as calcium. Since these elements belong to same group 2 and also have two electrons in their outermost shell like calcium.

 Electronegativity. 

Chlorine does not belong to the set. This is because Oxygen, Nitrogen, Carbon, Fluorine and Boron are the 2^nd period elements whereas Chlorine belongs to the 3^rd period. 

If an element has seven electrons in its outermost shell then it is likely to have the smallest atomic size among all the elements in the same period.

(i) Outermost shell complete – Noble gases

(ii) Outermost shell incomplete – Representative elements

(iii) two outermost shell incomplete – Transition elements

(iv)one electron short of octet – Halogens

(v) two electrons in the outermost orbit - Alkaline Earth metals

The seventh period is considered as an incomplete period because there are still vacant spaces for the elements to be discovered or artificially prepared. 

1. D 

2. F, G, H 

3. C 

4. N 

5. L 

6. M

a) D 

b) D 

c) M 

d) G, H 

e) L 

f) B 

g) M, N 

h) F

The horizontal rows are known as periods and vertical columns in the periodic table are known as groups

Valency is the combining capacity of the atom of an element. It is equal to the number of electrons an atom can donate or accept or share. It is just a number and does not have a positive or negative sign.

Group 1 elements have 1 electron in their outermost orbital, while Group 7 elements have 7 electrons in their outermost orbital.

Valency depends on the number of electrons in the outermost shell (i.e. valence shell).If the number of electrons present in the outermost shell is 1, then it can donate one electron while combining with other elements to obtain a stable electronic configuration.

If the number of electrons present in the outermost shell is 7, then its valency is again 1 (8 - 7 = 1) as it can accept 1 electron from the combining atom.

In a given period, the number of electrons in the valence (outermost) shell increases from left to right. But the valency increases only up to Group 14, where it becomes 4, and then it decreases, that is, it becomes 1 in Group 17.

1. Elements with large difference in properties were included in the same group. 

eg. Hard metal like copper [Cu], Silver [Ag] were included along with soft metals like sodium [Na] potassium [K], 

2. No proper position could be given to element hydrogen. Non-metallic hydrogen was placed along with metals like sodium [Na] and potassium [K] 

3. The increasing order of atomic mass was not strictly followed throughout.

eg. Co and Ni, Te and I 

4. As isotopes are atoms of same element having different atomic masses, they should have been given different position while arranging them in the order of atomic mass. But this was not done.

1. For the first time elements were comprehensively classified in such a way that elements of similar properties were placed in the same group. This has made the study of chemistry easy. 

2. When the classification was made in such a way that the elements of similar properties came in the same group. It was noticed that certain their proper group. The reason for this was wrongly determined atomic masses and consequently, those wrong atomic masses were corrected. 

Eg. The atomic mass of beryllium was known to be 14. Mendeleev reassessed it as a and assigned beryllium a proper place.

3. Columns were left vacant for elements which were not known at the time and their properties were predicted also. This gives an impetus to experiments in chemistry. 

Ex Mendeleev give names Eka aluminum and Eka silicon to those elements which were to come below aluminum and silicon respectively in the periodic table and predicted their properties. Later when these elements gallium and germanium were discovered the prediction of Mendeleev turned out to be true.

Newlands arranged elements in the increasing order of atomic mass. He noticed that every eighth element has properties similar to those of the first elements. But this peculiarity could be noticed in elements upto calcium only.

Octaves of Newlands

(a) The number of valence electrons increases by one as we move across any given period.

Therefore as we move from Lithium to Neon in period 2, the valence electrons will increase from 1 to 7.

(b) The metallic character decreases as we move from left to right while the non metallic character increases.

Ongoing from left to right in a period, the chemical reactivity of elements first decreases and then increases.

For example in period 3, Sodium is the most reactive metal and Chlorine is the most reactive non-metal and Silicon is least reactive

(c) The oxides of metals are basic and that of non-metals are acidic in general. Therefore since metallic strength decreases and non-metallic strength increases on moving from left to right across a period, the strength of basic oxides decreases, while the strength of acidic oxides increases.

For example, sodium forms a basic oxide, while sulphur and phosphorus form acidic oxides.