(a) What is a period in a periodic table? How do atomic structures (electron arrangements) change in a period with the increase in atomic numbers from left to right?
(b) How do the following change on going from left to right in a period of the periodic table?
(i) Chemical reactivity of elements (ii) Nature of oxides of elements
Give examples in support of your answer.
(a) What is a period in a periodic table? How do atomic structures (electron arrangements) change in a period with the increase in atomic numbers from left to right?
(b) How do the following change on going from left to right in a period of the periodic table?
(i) Chemical reactivity of elements (ii) Nature of oxides of elements
Give examples in support of your answer.
(a) A period is a horizontal row of elements in a periodic table. As the atomic number increases from left to right in a periodic table, the size of the atom decreases.
(b) (i) On moving from left to right in a period of the periodic table, the chemical reactivity of the elements first decreases and then increases.
For example, in the third-period elements comprising of Na, Mg, Al, Si, P, S and Cl, sodium (Na) is very reactive as it has one valence electron, and can, therefore, lose its electron easily. The chemical reactivity gradually decreases as we go to aluminium (Al) and silicon (Si). This is because the number of valence electrons increases, making it difficult to lose electrons. Moving further right in the period towards non-metals, the chemical reactivity again gradually increases. Phosphorus (P) has 5 valence electrons and needs 3 electrons to complete its octet. Sulphur (S) has 6 valence electrons and needs 2 more electrons to complete its octet. Chlorine (Cl) has 7 valence electrons and needs only one more electron to complete its octet. As chlorine can easily accept an electron as compared to phosphorus and sulphur, the chemical reactivity increases from phosphorus to chlorine.
(ii) On moving from left to right in a period of the periodic table, the basic nature of oxides decreases and their acidic nature increases. For example, taking the third-period elements again, the oxides of sodium are highly basic whereas those of chlorine are highly acidic.
(a) A period is a horizontal row of elements in a periodic table. As the atomic number increases from left to right in a periodic table, the size of the atom decreases.
(b) (i) On moving from left to right in a period of the periodic table, the chemical reactivity of the elements first decreases and then increases.
For example, in the third-period elements comprising of Na, Mg, Al, Si, P, S and Cl, sodium (Na) is very reactive as it has one valence electron, and can, therefore, lose its electron easily. The chemical reactivity gradually decreases as we go to aluminium (Al) and silicon (Si). This is because the number of valence electrons increases, making it difficult to lose electrons. Moving further right in the period towards non-metals, the chemical reactivity again gradually increases. Phosphorus (P) has 5 valence electrons and needs 3 electrons to complete its octet. Sulphur (S) has 6 valence electrons and needs 2 more electrons to complete its octet. Chlorine (Cl) has 7 valence electrons and needs only one more electron to complete its octet. As chlorine can easily accept an electron as compared to phosphorus and sulphur, the chemical reactivity increases from phosphorus to chlorine.
(ii) On moving from left to right in a period of the periodic table, the basic nature of oxides decreases and their acidic nature increases. For example, taking the third-period elements again, the oxides of sodium are highly basic whereas those of chlorine are highly acidic.
