Periodic Classification Of Elements - MCQ Test (22-11-2017) - Class 10 MCQ

The vertical columns in a periodic table are called groups and there are 18 groups in the long form of periodic table.The horizontal rows of elements in a periodic table are called periods and there are 7 periods in the long form of periodic table.

The halogens are located on the left of the noble gases on the periodic table. These five toxic, non-metallic elements make up Group 17 of the periodic table and consist of: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Although astatine is radioactive and only has short-lived isotopes, it behaves similar to iodine and is often included in the halogen group. Because the halogen elements have seven valence electrons, they only require one additional electron to form a full octet. This characteristic makes them more reactive than other non-metal groups.

All the elements of group 18 have 8 valence electrons each in their atoms, except helium which has only 2 valence electrons in its atom as its duplet is complete.

Due to their stable inert gas configuration, they are highly unreactive. Therefore, both statements (A) and (B) are correct.

As we move from left to right in a period, the positive charge increases due to gradual increase in the number of protons. So, the valence electrons are pulled in more strongly by the nucleus and it becomes more and more difficult for the atoms to lose electrons. Thus, on moving from left to right in a period, the tendency of atoms to lose electrons decreases i.e electropositive character of elements decreases.

When one electron has been removed from the neutral gaseous atom, the positively charged ion formed has one electron less than the number of protons in the nucleus. As a result, the electrostatic attraction between the nucleus and the remaining valence electrons increases. Therefore, the second ionization enthalpy is greater than the first one.

According to Dobereiner's law of triads, when elements are arranged in the order of increasing atomic masses, groups of three elements having similar chemical properties are obtained. The atomic mass of the middle element of the triad is equal to the arithmetic mean of the atomic masses of the other two elements.

Isoelectronic ions are those which contains the same number of electrons.
O^2- = 8+2 = 10 electrons
N^3- = 7+3 = 10 electrons
Na⁺ = 11-1 = 10 electrons
F^- = 9+1 = 10 electrons

Since the number of vallence electrons in a group is the same, all the elements in a group have the same valency.

As the atomic number is 16, therefore, the valence electrons will be 6.
To complete its octet, it will gain two electrons and so  will exhibit Non-metallic character.

Mendeleev left proper gaps in his periodic table for the then undiscovered elements, and when Gallium(Ga)  was discovered it was placed in one of those gaps without disturbing the existing elements. 

Isotopes of an element  are the atoms with same atomic number but different atomic masses. Being the atoms of the same element, they possess similar chemical proeprties.

³⁵₁₇Cl and ³⁷₁₇Cl are the isotopes of Chlorine.

The valency of the element of group 13 is 3, (13-10=3)
and oxygen has the valency of 2. So, formula of the oxide will be P₂O₃.

Elements of group 1 can readily lose 1 electron to complete their octet.
Elements of group 17 need one electron to complete their octet. So, both of them combine with each other and form ionic compounds.

An element with atomic no 3 has electronic configuration 2,1 i.e. it can lose one electron readily to complete its duplet. 
​The element with atomic no 17 has electronic configuration 2,8,7 and is ready to accept one electron to complete its octet. 
So,  both of them with valency 1 combine and the formula is LiCl. 

According to Dobereiner's law of triads when elements are arranged in the order of increasing atomic masses, groups of three elements having similar chemical properties are obtained. The atomic mass of the middle element of the triad is equal to the arithmetic mean of the atomic masses of the other two elements. 

Li, Na, K form the triad of alkali metals and Cl, Br and I form the triad of halogens. 

The element with atomic number 20 is Calcium(Ca) and it has metallic character as it loses it two valence electrons easily to complete its octet.

On going down the group of the periodic table, the electronegative character of non-metals decreases.
Therefore, Fluorine being on the top in group 17 elements have the most electronegative character.

They are called Periods and we have seven periods in the long form of periodic table.

Sodium and Potassium are the group 1 elements as they have 1 valence electron in their outermost shells.
Magnesium and Calcium are group 2 elements as they have 2 valence electrons in their outermost shells.

The group 3 to group 12 elements are called Transition elements. In these elements, the outermost shell as well as the next to outermost shell are incomplete and in the process of being filled with electrons.

The elements on the extreme left of the periodic table have the largest size.
K, being on the extreme left of all the elements given have the largest size as on moving from left to right in a period, the size of atoms decreases. 

Neon(Ne)  with atomic number 10 has an inert gas configuration 2,8 where both the shells have completely filled electrons. 

All the elements of a group have the same number of valence electrons i.e Fluorine belongs to group 17 and all the elements have 7 valence electrons.
To complete their octet, they accept one electron readily and therefore they are electronegative elements with valency 1.

Electronic configuration of Al is 2,8,3
To form Al³⁺ , electronic configuration of Al is 2,8.

This is because Mg has a valency of +2 and would easily give its two electrons to complete its outermost electronic configuration. 
So, it combines with chlorine to form XCl₂

Hydrogen has an anomalous behaviour, it can behave as a metal as well as a non-metal.
It has 1 electron and 1 proton but no neutrons.

All the elements beyond atomic no 92 are prepared in laboratory and so are called as Synthetic elements.

Electronic configuration of Mg is 2,8,2
To complete its octet, it will lose two electrons readily and form divalent ion, Mg²⁺.

On moving from left to right in a period, the electropositive character of element decreases i.e. it becomes difficult for elements to lose electrons and form positive ions.