Bond Length Trends (Molar Mass)

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Steven Garcia 1H
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Joined: Fri Sep 28, 2018 12:16 am

Bond Length Trends (Molar Mass)

Postby Steven Garcia 1H » Thu Nov 29, 2018 7:38 pm

The textbook mentions that "bonds between heavy atoms tend to be larger than those between light atoms because heavy atoms have larger radii than lighter ones". However, I'm a little confused with this idea. For example, if you go across a period, the atomic mass of the elements increase. Yet, we know that as we go across a period the atomic radii of the atoms decrease due to a stronger effective nuclear charge. Therefore, in this case we have heavier atoms that actually have a smaller radii.

Does this rule only apply to atoms going down a group?

Deepika Pugalenthi 1A
Posts: 60
Joined: Fri Sep 28, 2018 12:24 am

Re: Bond Length Trends (Molar Mass)

Postby Deepika Pugalenthi 1A » Thu Nov 29, 2018 7:45 pm

When I read that in the book, I thought of heavy and light as referring to the number of electrons the atoms had. The more electrons an atom has (heavier), the larger the radius will be, leading to an increased bond length. And the reverse applies for atoms with a lower number of electrons (lighter). Since radii are mainly focused on the number of electrons and electrons don't comprise a substantial part of the molar mass, I don't think you should take the words heavy and light to a literal meaning. I hope this helps!

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