Chemistry Notes 2nd year Chap 1

Impotant Questions
Q1 :  Lanthanide cotraction controls the atomic size of the elements of the 6th and the 7th period ?
   
Ans : Lanthanides are presend in the 6th period and anitinides are the members of 7th periods. In case of Lanthanides and anticides the valance electrons are entering in  the 4f & 5f orbitals repectively where they experiences more nuclear pull due to increased affective nuclear charge which causes decrease in atomic size (lanthanide contrqction). That is why the atomic sizes of lanthanides and actinides and antinides are effected by the lanthanide contraction.

Q2 : Explain why 'D' and 'F' blocks are called transition elements ?

Ans : d-block and f-bock elements are present in between the s & p block elements in thr modern periodic Table. their properties are in between the s & p-block elements varying from left to right. It means that their properties show a sysmatic transtional phase from metallic non metallic behaviour therefore they are called transition elements.

Q3 : Oxidation states vary in a period but remain almost constant in group ?

Ans : Oxidation state depends upon no unpaired of electrons present in tha vallance shell. Since the no of electrons present in the valnce shell remain same in the group so oxidation state remain same down the group on moving from left to right the num of electrons vary so the oxidation state of atom also change across the period

Q4 : The hydration energies of  ions are in the following order Al+3 > Mg+2 > Na+1

Ans : Hydration energies depends upon the cahrge density of ions i.e Greater the charge density more will be the hydration energy. Charge to siza (charge density ) is maximum for the Al+3 and minimum for the Na+1. Therefore the hydration energies are in the order.

Q5 : Alkali metals give ionic hydrides ?

Ans :  Hydrides are the binary compounds of  Hydrogen. Their nature depends upon the type of bonding present in them. Since alkali metals are much more electropostive than the hydrogen so the lose the electron and give it to hydrogen forming the postive ion and hydrogen the negtive ion. Since bond is formed between metal and hydrogen due to transfer of electron hence ionic hydrides are formed.

Q6 : Altough both sodiun and phosphorus are present in the same period of the periodic table yet their oxides are different in nature Na2O is the basic and P2O5 is acidic in nature ?

Ans : The nature of oxides depends upon the nature of element forming oxides. When moving from left to right there is change in metalic character from left to right i.e at the left matal at the right metal nonmetals
Metals from basic oxides and nonmetals from acidic oxide that is why both sodium and phophorus are present in the same period of the periodic table yet their oxides are different in nature Sodium being metal forming the basic oxides Na2O and Phosphorus being nonmetal forming acidic oxides P2O5.

Q7 :Ionic character of halides decreases from left to right in a period ?

Ans : Ionic character of halides depends upon the difference of electronegativity of bonded atoms. As we remove from left to right across the period the electronegativity of element increase and difference with respect to halogen decrease hence the ionic character of halides decrease across the period.

Q8 : Why the oxidation state of noblie gases is usually zero ?

Ans : noble gases have completely filled s & p orbital of their vallance shell. Due to this stable electronic configuration they canot gain or lose the electron hence they show usually zero oxidation state.

Q9 : Why diamond is a non-conductor and graphite is a good conductor ?

Ans : In case of diamond, all the four calance electrons of carbon are tetrahedrally bonded with the neighouring hence not free electrons are available for conduction so it is the poor conductor of electricity whereas in case of graphite one electron is free along the layer of atom which carry the current hence graphite is good conductor.

Q10 : Describe essential features of period number six of periodic table ?

Ans : It is the longes period of periodic table having 32 elements. in this period there are eight representative elements, ten transition elements and fourteen elements of Actinides starting from 89Ac.

Q11 : Why the alkali metals are strong reducing agent ?

Ans : Because lower ionization energies, alkali metals readily lose the valance electron hence they act as the reducing agent.

Q12: Why hydrogen can be placed at the top of group 1-A,4-A, & 7-A of the periodic table ?

Ans :  In the periodic table elements are placed according to their electronic configuration into groups and periods. Hydrogen possess one electron in the outer most shell like alkali metals,  Hydrogen possess half-filled valance shell like 4A group and needs one electron complete its outer most shell like halogens so it can be placed at the top of group 1-A, 4-A & 7-A of the periodic table.

Q12 :  What are covlant halides ? give two examples.

Ans :  The binary compouds of halogen formed by sharing the electrons are called covlant halides.
Examples are SiCl4 , PCl3 & S2Cl2

Q13 : Define group and period . How many elements are there in period number 1 ?

Ans : Vertical column in the periodic table are called groups whereas the horizentle rows are called the periods. There are seven periods and eight groups in the periodic table. Two elements Hydrogen and Helium are present in first period.

Q14 : Define Lanthanide contraction ?

Ans : The grdual decrease in atomic and onic radii with increasing atomic number among the lanthanides elements with atomic number from 51 to 71 lanthanide contraction. The decrease arises because of a gradual increase in effective nuclear charge trough the lantanide series.

Q15 : State modern Periodic Law ?

Ans :  Physical and chemical properties of alements are the periodic function or their atomic numbers.