Question

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1. electrons in the 2s subshell are closer to the nucleus in which of the following nuclei? a. He c. Rb e. F i Cd Б. Хе d.Co f. Ni h. Rnj. H g. K از ره ره ر؟ CAL. C h iab berdar..

Answer 1

1. To answer this question we need to know shielding of electrons by subshells. 1s, 2s these are very close to nucleus and effective attractive forces on it is very much high. That's why these are called core shells which shield the outer shells or valence shells from nuclear attraction. This shielding is depends on effective nuclear charge Z_{​​​​​​eff} which is defined as Z_{​​​​​​eff} = Z - S where Z = atomic number and S = core shell electrons. More the effective nuclear charge more the effect of shielding and 2s electrons are more closer to the nucleus.

By the discussion and with the help of periodic table we can say that F has the highest effective nuclear charge as it has atomic number of 9 and 2 core shell electrons. So it gives Z_{​​​​​​eff} = 7. For this reason 2s electrons are more closer to nuclei for Fluorine.

2. Cooling of water per gram is will be most by the compound is MgF2. Because it is most ionic compound in water it will ionize and will give 3 ions i.e. two F ions and one Mg ions.

Cooling of water depends on the vant Hoff factor of the compound which given by no of ionized species in the solution. More the vant Hoff factor more will be the cooling. Next thing is ionization which is depends on the size of associated atoms in the compounds.

Taking those considerations MgF2 is the best candidate.