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Chemistry XII Chapter

Question number 1.6: The oxidation states vary in a period but remain almost constant in a group.
Answer: 
An appearent charge on an element in a compound due to loss or gain of electron is called its oxidation state. Oxidation state of elements is closely related to number of valence electrons of their atoms. In a group, number of valence electrons in atoms of elements remains the same, so their oxidation state also remains constant. But in a period, as we move from left to right, the number of valence electron increases by one unit in each element. So oxidation state of elements varies in a period.

Question 1.7: hydration energy of ions is in following order:
Al3+>Mg2+>Na+
Answer: Hydration energy is the amount of energy released when 1 mole of ions are surrounded by  excess amount of water. Hydration energy of  ions depends upone charge density of ions. Greater the charge density smaller the hydration energy and vice versa. For instance, Na has smaller charge and larger size, so its charge density is low. Hence, its hydration energy is very low. The magnesium ion has greater charge and small volume, so its charge density is high. Therefore, its hydration energy is relatively high. The aluminium has highest charge and smallest size so it's hydration energy is very high.

Question 1.8: ionic character of halides decreases from left to right in a period 
Answer: Ionic character of halides is dependent upon the electronegativity difference between bonded atoms. The greater the electronegativity difference, higher is the ionic character. Moving from left to right in a period, electronegativity of  elements goes on increasing due to gradual increase in their nuclear charge and decrease in atomic size. At the same time, their difference of electronegativity with respect to halogens decreases, as a result ionic character also decreases.

Question1.9: Alkali metal give ionic hydride.
Answer: 
The hydride  in which  hydrogen is bonded with  other elements through an ionic bond is called  ionic hydride. Alkali metals form ionic hydride because they have very low ionization energy. So, they can lose their valence electron very easily to form alkali metal cation and hydrogen has more electron affinity and can form hydride ion. It is the reason that alkali metals form ionic hydride.

Question 1.10: Although both Sodium and phosphorus present in the same period of periodic table but their oxides are different in nature, Na2O is basic while P2O5 is acidic in nature.
Answer: NaO is a basic because it forms a base when reacts with water. P2O5 is an acidic because it reacts with water to form an acid. Strength of a basic oxide depends upon metallic character of metal. Usually metals form basic oxide and non metal form acidic oxide. When we move from left to right across the road, basic character decreases and acidic chacter increases due to decrease in metallic character.

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