Molecular Shapes Overview

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Questions and Answers

Which shape corresponds to a molecule with two bonding pairs and a bond angle of 180 degrees?

  • Nonlinear
  • Linear (correct)
  • Trigonal planar
  • Pyramidal

Lone pairs exert less repulsion than bonding pairs.

False (B)

What bond angle is associated with a tetrahedral shape?

109.5 degrees

In a molecule with four bonding pairs and no lone pairs, the shape is __________.

<p>tetrahedral</p> Signup and view all the answers

Match the following molecular shapes with their corresponding bond angles:

<p>Linear = 120 degrees Trigonal planar = 180 degrees Pyramidal = 107 degrees Octahedral = 90 degrees</p> Signup and view all the answers

What is the result of lone pairs on bond angles?

<p>They reduce bond angles by 2.5 degrees for each lone pair. (A)</p> Signup and view all the answers

A molecule with five bonding pairs is likely to have a trigonal bipyramidal shape.

<p>True (A)</p> Signup and view all the answers

Provide an example of a molecule with a nonlinear shape and how many bonding and lone pairs it has.

<p>Water (H2O), 2 bonding pairs and 2 lone pairs</p> Signup and view all the answers

For a molecule with 3 bonding pairs and 1 lone pair, the bond angle is reduced to __________ degrees.

<p>117.5</p> Signup and view all the answers

What is the bond angle in an octahedral shape?

<p>90 degrees (A)</p> Signup and view all the answers

Flashcards

Linear Shape

The central atom is surrounded by two bonding pairs of electrons, resulting in a straight line shape with a 180 degree bond angle.

Trigonal Planar Shape

The central atom is surrounded by three bonding pairs of electrons and no lone pairs, forming a flat triangular shape with 120 degree bond angles.

Bent or Angular Shape

A central atom with three electron pairs (two bonding, one lone), creating a bent or angular shape. The angle is less than 120 degrees due to the repulsion of the lone pair.

Tetrahedral Shape

The central atom is surrounded by four electron pairs, with all of them being bonding pairs. It creates a pyramid-like shape with four equal sides and 109.5 degree bond angles.

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Pyramidal Shape

A central atom with four electron pairs (three bonding, one lone), resulting in a pyramid-like shape, but with a lone pair at the top. The bond angle is slightly smaller than 109.5 degrees due to lone pair repulsion.

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Bent or V-Shaped, Nonlinear Shape

A molecule with a central atom surrounded by four electron pairs (two bonding, two lone), creating a bent shape. The bond angle is significantly less than 109.5 degrees because of the increased repulsion from the two lone pairs.

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Trigonal Bipyramidal Shape

The central atom has five electron pairs, all of which are bonding pairs. The shape is a combination of two pyramids sharing a common base, with 90 degrees between the vertical and horizontal arms, and 120 degrees between the horizontal arms.

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Octahedral Shape

This shape has six electron pairs, all of which are bonding pairs. The central atom is surrounded by six atoms in a symmetrical, three-dimensional shape with all angles being 90 degrees.

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Lone pair Repulsion

Lone pairs repel bonding pairs more strongly than bonding pairs repel each other.

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Electron pair Repulsion

The repulsion between electron pairs determines the shape of a molecule. Equal repulsion results in symmetrical shapes, while uneven repulsion leads to asymmetric shapes.

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Study Notes

Molecular Shapes

  • To determine molecular shapes, start with a simple dot-and-cross diagram.
  • Identify the number of electron pairs (bonding and lone) around the central atom. Multiple bonds count as a pair of electrons.
  • Count the number of bonding pairs and lone pairs.
  • Analyze repulsion: Equal repulsion occurs when all electron pairs are bonding. Lone pairs repel more strongly than bonding pairs.
  • Determine the associated shape and bond angle based on electron pair repulsion.

Shape Examples

  • Two electron pairs (both bonding): Linear shape; 180° bond angle (e.g., CO2)
  • Three electron pairs (all bonding): Trigonal planar shape; 120° bond angle (e.g., BF3)
  • Three electron pairs (one lone pair): Bent shape; ≈ 117.5° bond angle (lone pairs reduce angle by ~2.5°).
  • Four electron pairs (all bonding): Tetrahedral shape; 109.5° bond angle (e.g., CH4)
  • Four electron pairs (one lone pair): Pyramidal shape; ≈ 107° bond angle (lone pair reduces angle).
  • Four electron pairs (two lone pairs): Bent shape; ≈ 104.5° bond angle (lone pairs reduce angle).
  • Five electron pairs (all bonding): Trigonal bipyramidal shape; 90°& 120° bond angles (e.g., PF5)
  • Six electron pairs (all bonding): Octahedral shape; 90° bond angles (e.g., SF6)

General Guidelines

  • Lone pairs reduce bond angles by approximately 2.5 degrees.
  • The shape is determined primarily by the arrangement of bonding pairs.

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