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CfE Advanced Higher Chemistry Unit 1 > Shape and Polyatomic molecules > Flashcards

Flashcards in Shape and Polyatomic molecules Deck (10)
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1

Which theory predicts the shapes of molecules and polyatomic ions?

Valence shell electron pair repulsion

VSEPR

2

How does Valence shell electron pair repulsion (VSEPR) theory work?

Shapes can be predicted from the number of bonding electron pairs and the number of non-bonding electron pairs.

3

How is the total of electron pairs calculated?

 

 

Electron pairs = (number of electrons on centre + number of bonded atoms)/2.

For NH3

5 outer electrons on the central nitrogen atom (electron arrangement 2, 5) + 3 hydrogen atoms bonded.

5+3=(8)/2 = 4 (3 bonded and 1 lone pair)

4

What arrangement of electron pairs would be found when the total number of electron pairs is 2, 3, 4, 5 and 6, respectively.

linear, trigonal (trigonal planar), tetrahedral, trigonal bipyramidal and octahedral

5

What arrangement of electron pairs would be found where we have:

 

i) 3 total electron pairs but 2 bonding pairs

ii) 4 total electron pairs but 3 bonding pairs

iii) 6 total electron pairs but 5 bonding pairs

 

i) Bent/angular

ii) Trigonal Pyramid

iii) Square pyramid

6

Electron pairs will repel each other. They can be bonded or non-bonding (lone) pairs.

What is the order of repulsive effect?

non-bonded pair:non-bonded pair > non-bonded pair:bonded pair > bonded pair: bonded pair

7

What effect do lone pairs have of the positions of bonded pairs?

They distort the shape.

8

What shape would Beryllium dichloride take?

Linear

9

What shape would hydrogen oxide take?

Bent/angular/non-linear

10

What shape would Boron trifluoride take?

Trigonal planar