Question

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Answer 1

Ranking of elements from most positive to most negative Electron Affinity :

Helium < Sodium < Arsenic < Tellurium < Fluorine

Step-by-step explanation:

Electron Affinity : The amount of energy released when an electron is added to the gaseous atom.

`X + e^(-)\rightarrow  X^(-)`

When energy is released then
`\Delta H` = negative

In most of the elements
`\Delta H` have negative values

• Helium is the stable gas as its outermost shell has 8 electron (complete octet). So it does not show any activity towards electron. Hence, its
  `\Delta H` value is 0 kJ/mol.
• Sodium has atomic number 11. Its electronic configuration is 1s(2)2s(2)2p(6)3s(1). Its show negligible affinity towards electron because of electron-electron repulsion due to small size of sodium.
  `\Delta H` = -53 kJ/mol.
• Arsenic belongs to Nitrogen family. Here also eletron-electron repulsion occurs on electron addition,but due to large size as compare to sodium its Electron affinity is more than Sodium.(-78 kJ/mol)
• Tellurium show high electron affinity because of its electronic configuration and large size (less repulsion between electrons).(-190 kJ/mol)
• Fluorine has second largest values(negative) of electron Affinity.Its electronic configuration is 1s(2)2s(2)2p(5).To complete its octet it readily capture electron and get stable.(-328 kJ/mol)