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Question
How does Chemical reactivity of elements change on going from left to right in a period of the periodic table?
Give example in support of your answer.
Solution
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.
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RELATED QUESTIONS
On moving from left to right in a period of the periodic table, the atomic number of elements increases. What happens to the size of atoms of elements on moving from left to right in a period?
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| Column I Elements | Atomic Number | Electronic Configuration | Underline the element present in that group |
| 1. Hydrogen | 1 | ______ | Be/Na/Ca |
| 2. Carbon | 6 | ______, ______ | N/P/Si |
| 3. Nitrogen | 7 | _______, ______ | C/P/S |
| 4. Oxygen | 8 | _______, ______ | N/S/Cl |
| 5. Sulphur | 16 | _____, ______, _______ | O/N/F |
| 6. Chlorine | 17 | _____, ______, ______ | I/O/S |
