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Explain why molecules of water and hydrogen sulfide have the same shape

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tamanimat | Student, Grade 11 | Salutatorian

Posted July 29, 2013 at 7:38 AM via iOS

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Explain why molecules of water and hydrogen sulfide have the same shape

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jerichorayel | College Teacher | (Level 1) Senior Educator

Posted July 29, 2013 at 4:12 PM (Answer #1)

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Looking at the periodic table, both oxygen and sulfur fall on the same group. Having the same group means that they have same valence electrons. Their valence electrons are 6.

Electron configuration of the valence electrons

`O = 2s^2 2p^4`

`S = 3s^2 3p^4`

If you will draw their Lewis structures for H2S and H2O, we can see that there are two lone pairs in the central atoms.

   ..
H-S-H
   ''

   ..
H-O-H
   ''

Based on the molecular geometry table (see reference), both of them have 2 bonding electron pair and 2 lone pairs. They both fall to the group `AX_2 E_2` which have the shape bent.

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llltkl | College Teacher | Valedictorian

Posted August 20, 2013 at 8:24 AM (Answer #1)

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For both `H_2O` and `H_2S` :

Number of valence electrons on the central atom (O/S): 6

Electrons shared during bond formation: 2

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Total: 8 electrons = 4 pairs

pi bonded pairs (if any): 0

---------------------------------------------------------------------

Number of structurally active electron pairs around the central atom: = 4-0 = 4

Hybridization: ,

Geometry: Tetrahedral,

Lone pairs=total electron pairs-number of bonds=4-2=2

-------------------------------------------------------------------------

Therefore, the tetrahedral shape will be modified, to an actual V-shape (or bent structure) for both the molecules.

However, difference in electronegativity and size of the central atom will bring about certain difference in the bond angles of the two molecules.

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