Classification-of-Elements-and-Periodicity

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Name some elements whose atomic weight was corrected by the arrangement of the elements in the Mendeleev's periodic table.

Gold (Au), platinum (Pt), Aluminium (AI) etc.

Write down the defect of Mendeleev's periodic table?

i) Anomalous position of hydrogen: Hydrogen is placed with alkali metals in group-I but it is non-metal and its property is similar to the halogens of group-VII.

ii) Anomalous pair of elements: Some elements having higher atomic weight precede the elements with lower atomic weight. For example Ar (Atomic weight 39.9) precedes K (Atomic weight 39.1). Similarly Co (Atomic weight 58.9) precedes Ni (Atomic weight 58.7)

iii) Position of isotope: If periodic table was made according to the increasing order of atomic weight then isotope should also have had position in the periodic table.

iv) Some dissimilar elements were placed together but some similar elements were placed in different group. For example CU, AG, AU etc. are placed in group I with alkali metals like Li, Na, k etc. But similar elements like Cu and Hg were placed in different group i.e. Group I and II respectively.

v) Position of lanthanides and actinides: There wasn't any place for lanthanides and actinides.

vi) Position of elements of group VIII was not clear because nine elements of group VIII were placed in the form of triad without any justification.

Write down modern periodic law.

The physical and chemical properties of elements are a periodic function of their atomic number.

Note: Mosley suggested that atomic number should be the basis of the classification after his one of the important experiments. He found that when high speed electron strikes a metal, x-ray produces. The frequency of x-ray depends upon atomic number of metal. So he suggested that atomic number should be the basis of classification.

Write down the difference between old periodic table and modern periodic table.

Mendeleev's Periodic table	Modern Periodic table
a) Elements were arranged in the order of increasing atomic weight.	a) Elements are arranged in the order of increasing atomic number.
b) There is not a fixed position for the lanthanides and actinides.	It provides a fixed place for the lanthanides and actinides.
c) There were 7periods and 8 groups of element.	c) There are 7periods and 9 groups of elements.
d) Position of isotope was not clear.	d) Isotopes are not taken in the table because elements are arranged in the order ok increasing atomic number not according to atomic weight.
e) In the place of one element there were two or three elements.	e) Element has its own place in the periodic table in a series i.e. from 1to 109.
f) Elements were divided into groups and periods only.	f) Elements are divided into groups, periods and 4 distinct blocks i.e. s,p,d & f blocks.

Mention the place of non-metals in periodic table and write down their names.

Non-metal are placed at the right hand side of the periodic table from group ''VA'' to '0'.

They are N, O, F, P, S, Cl, Se, Br, I, At (Astatine) and 'o' Group elements.

What are metalloids? Name any 3 metalloids.

Elements which lie between metal and non-metal of the periodic table and possess both the metallic and non-metallic character are called metalloids.

Silicon (Si), germanium (Ge), and bismuth
(Bi)

Why the elements of group IA are called alkali metal?

The metallic oxide of the metal of group IA dissolves in water to form alkali. So they are called alkali metal.

Why the elements of group IIA are called alkali earth metal?

The metallic oxide of the metal of group IA dissolves in water to form alkali, further their oxides and carbonates are abundantly present on the earth crust. So they are called alkali earth metal.

Why the properties of elements of one group of periodic table are similar?

Elements of same group of periodic table contains same number of electrons in the outer most orbits of their atoms due to similar electronic configuration. Therefore they have similar chemical and physical properties.

Why the properties of the elements of different group of periodic table are different?

Elements of different group of periodic table contain different number of electrons in the outer most orbit of their atom. Therefore they have different chemical and physical properties.

Why the properties of the elements of different group of periodic table are different?

Elements of different group of periodic table contain different number of electrons in the outer most orbit of their atom. Therefore they have different chemical and physical properties because these electrons are responsible to take part in the chemical reaction.

Why the elements of group IA of periodic table are known as highly reactive metals?

Except hydrogen; lithium, sodium, potassium etc. of first group of periodic table are metals. They have only one electron in the outermost orbit of the atoms. So they react easily and quickly with other elements by the donation of one electron of their outermost orbits. Therefore they are called highly reactive metals.

Why the elements of group VIIA of periodic table are known as highly reactive non-metal?

Fluorine, chlorine, bromine, iodine etc. of group -VII of periodic table are non-metals and their atoms contain 7 electrons in the outermost orbit. So they react easily and quickly with other elements by sharing electrons or by accepting one electron. Therefore the elements of group VII of periodic table is known as highly reactive non-metals.

Why the elements of group '0'of periodic table are knows as insert gases?

Helium, Neon, Argon, Krypton etc. of 'Group-0' of the periodic table are gases. Their outermost orbit is fulfilled with the electrons either by 8 electrons (octet) or by 2 electrons (duple).Since an element takes part in chemical reaction to complete the number of electrons in their outer most orbits, therefore they do not react with other elements and are known as insert gas.

Write down characteristics of modern (new) periodic table.

1. Elements are divided into 9 groups (18 columns) and 7 periods (rows).

2. Lanthanides and actinides are placed differently at the bottom of the periodic table.

3. Elements are divided not only into the groups and periods but they are also divided into 4 distinct blocks i.e. s, p, d and f-block elements.

4. Elements of Gr-VIII of old periodic table like Fe, Co, Ni, etc. are taken as transition elements and are placed in the order of transition elements between Gr. II A and IIIA.

5. Elements are arranged in the order of their increasing atomic number from left to right of the table.

What are representative elements?

Elements of group -IA, IIA, IIIA, IVA, VA, and VIIA are called representative elements in which the outermost orbit of the atoms are not fulfilled with the number of electrons. They are s-block and p-block elements except noble gasses.

_{Why hydrogen is placed in group IA of periodic table?}

Like Li, Na, K etc. of Gr-I of periodic table, hydrogen also reacts with halogens (fluorine, chlorine etc.) as an electropositive elements.

Hydrogen can be placed in group VIIA of periodic table? Why?

Following are the reasons:

i) It is a gas at the ordinary temperature like some halogens of group -VIIA of periodic table.

ii) Like halogens, its molecule it's diatomic.

iii) Metals form halides with the halogens like NaCl, KBr etc. and similarly some metals form hydrides with hydrogen e.g. NaH,KH,CaH₂ etc.

iv) If it were placed in 'Group-VIIA'' there would not be a blank space for six elements between hydrogen and helium.

Why the elements of Group-VIIA of periodic table are known as halogens.

'Hale' means 'sea-salts' and 'genes' means 'produce'. So, halogen means sea-salt producer. This name is given to the elements of Gr-VIIA (F, Cl, Br etc.) of periodic table because chlorine produce sea-salt i.e. sodium chloride and other elements have also the tendency to form salts.

Why ''Alkali metals'' are placed in 'Group-IA' of periodic table.

Because alkali metals contain one electron in their outermost orbit. They can easily remove their valence electron and they form salt combining with VIIIA group elements.

What is transition element?

The element which lies in between highly reactive metals and non-metals i.e. from group IIIB to IIB of periodic table are called transition elements.

Why transition metals have variable valency?

In case of transition metals, both the outermost and inner shells are not fulfilled with the electrons. Sometimes, only the electrons of the outermost orbit and sometimes the electrons of the inner orbit also take part in chemical reaction so their valency differ according to the number of electron that take part in chemical reaction.

What are lanthanides and actinides?

After the element Lanthanum (At.No.-57), a series of 14 elements i.e. 'Cerium'(At.No.-58) to Lutetium (At.No.-71) and after Actinium (At.No.-89) another series of 14 elements i.e. Thorium (At.No.-90) to Lawrencium (At.No.-103) are called lanthanides and Actinides respectively.

(In both the series their f-sub shell is being filled with electrons so they are knowns as f-block elements and are placed at the bottom of the periodic table. They are also known as inner transition element.)

What are duplet and octet?

The condition of the elements having capacity to hold maximum two electrons in the outermost orbit of its atom is known as duplet.

The condition of the element having capacity to hold maximum eight electrons in the outermost orbit of its atom is known as octet.

What do you mean by 2n² rule of electron configuration?

It is a rule that gives the maximum number of electrons that an orbit of the atom can hold. Here 'n' represents number of orbit. According to this rule first orbit, 2nd orbit and 3rd orbit can hold 2, 8, and 18 electrons respectively.

First orbit (n=1)

2n² = 2*1² =2*1=2

Second orbit (n=2)

2n²=2*2²=2*4=8