Determine the electron and molecular geometries of each molecule. (Hint: Determine the geometry around each of the two central atoms.)

(a) \(\mathrm{C}_{2} \mathrm{H}_{2}\) (skeletal structure HCCH)

(b) \(C_{2} H_{4}\) (skeletal structure \(\mathrm{H}_{2} \mathrm{CCH}_{2}\))

(c) \(C_{2} H_{6}\) (skeletal structure \(\mathrm{H}_{3} \mathrm{CCH}_{3}\))

Equation Transcription:

Text Transcription:

C_2 H_2

C_2 H_4

C_2 H_6

H_2 CCH_2

H_3 CCH_3

Solution 70P

Here, we are going to find out electron and molecular geometries of each molecule.The bond angles can be calculated by using VSEPR theory. The repulsion between the electron groups of the internal atom determines the geometry of the molecule. The best possible geometry of the molecule is that where electron groups have maximum separation between them. The VSEPR notation for a molecule is as follows

AXn, where "A" and n represents central atom and the number of bonds with the central atom respectively.

When lone pair of electrons are present in a molecule, then the VSEPR notation will be AXnEn, where En is the number of lone pair of electrons present on the central atom.,

Electron group geometry depends on the number of electron groups around the central atom.

Molecular geometry of the molecule can be determined by electron groups as well lone pair of electrons.

(a) C2H2 (skeletal structure HCCH)

The valence electron of C = 4

Valence electron of H atom = 2

Total valence electrons in C2H2 molecule = 2x4+2 =10 e

The Lewis structure of C2H2 is

The geometry of each interior atom is as follows.

Central Element |
No. of electron groups |
No. of lone pair of electrons |
Molecular geometry |

C |
2 |
0 |
linear |

C |
2 |
0 |
Linear |

Using the geometry of interior atom, the geometry of the molecule will be.

Thus, the electron geometry of the molecule is = Linear (having two electron groups) and

The molecular geometry of the molecule is = linear

(b) C2H4 (skeletal structure H2CCH2)

The valence electron of C = 4

Valence electron of H atom = 2

Total valence electrons in C2H4 molecule = 2x4+4 =12 e

The Lewis structure of C2H4 is

The geometry of each interior atom is as follows.

Central Element |
No. of electron groups |
No. of lone pair of electrons |
Molecular geometry |

C |
3 |
0 |
Trigonal Planar |

C |
3 |
0 |
Trigonal planar |

Using the geometry of interior atom, the geometry of the molecule will be.

Thus, the electron geometry of the molecule is =trigonal planar (having three electron groups) and

The molecular geometry of the molecule is = Trigonal planar

(c) C2H6 (skeletal structure H3CCH3)

The valence electron of C = 4

Valence electron of H atom = 2

Total valence electrons in C2H6 molecule = 2x4+6 =14 e

The Lewis structure of C2H6 is

The geometry of each interior atom is as follows.

Central Element |
No. of electron groups |
No. of lone pair of electrons |
Molecular geometry |

C |
4 |
0 |
Tetrahedral |

C |
4 |
0 |
Tetrahedral |

Using the geometry of interior atom, the geometry of the molecule will be.

Thus, the electron geometry of the molecule is =Tetrahedral (having four electron groups) and

The molecular geometry of the molecule is = Tetrahedral (having four electron groups and no lone pair of electrons)