1.4 theories of covalent bonding ppt

1.4 theories of covalent bonding ppt - Introductory...

Info iconThis preview shows pages 1–16. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Introductory University Chemistry I Theories of Covalent Bonding Introduction • The VSEPR is good for predicting molecular shapes • It does not provide the roles of the atomic orbitals in bond formation. • It does not provide explanations for bond energy, magnetic and spectral properties in covalent compounds. Theories are required to explain covalent bonding. Two theories for covalent bond formation • Valence Bond (VB) Theory Focuses on overlapping of atomic orbitals olecular Orbital (MO) Theory • Molecular Orbital (MO) Theory Focuses on orbital energy levels They compliment each other for a full picture of covalent bond formation Valence Bond Theory The VB Theory provides a qualitative approach to covalent bonding. Three main themes for the VB Theory : 1 For covalent bond to form, the atomic orbitals must overlap . + 1s H H H H 1s 1s 1s 1s F F 2p 2p + F F 2p 2p F F F F F H 1s 2p H F + 1s 2p F HF The orbitals must be of the same phase for overlapping The more effective is the overlapping, the stronger is the bond Valence Bond Theory Three main themes for the VB Theory : 2 For covalent bond formation, the electron must be of opposite spin . What would happen if the two electrons are of the same spin? No covalent bond can form. Valence Bond Theory Formation of methane (CH 4 ) Electron configuration of carbon is: 1s 2 2s 2 2p x 1 2p y 1 2p Electrons from hydrogen 2s 1s Energy With this configuration, only a maximum of two bonds for carbon. The compound would then be CH 2 Valence Bond Theory Excitation of electron allows four bond formation 2p Energy 2p Energy 2s 1s Energy Excitation and change of spin 2s 1s Valence Bond Theory Problems arise: • Inconsistency of bond angle Bond angles expected = 90 o (compared with 109.5 o ) • One hydrogen atom is unable to overlap with the inner 2s orbital H H H H 2s orbital Valence Bond Theory Three main themes for the VB Theory : 3 For effective overlapping, the atomic orbitals hybridize to form four equivalent orbitals . The process of atomic orbital mixing is called hybridization and the new atomic orbitals are called hybrid orbitals . sp 3 sp 3 sp 3 sp 3 2s 2p 1s Energy 1s Hybridization Hybridization of carbon sp 3 means one s orbital and three p orbitals are combined Structure of methane H C H • Four sp 3 orbitals give rise to a tetrahedron (109.5 o ) (consistent with four electron groups from VSEPR) • Four single bonds ( σ bonds): sp 3 (C) to 1s (H) H H From VSEPR Hybridization • The number of hybrid orbitals = number of participating atomic orbitals 2s + 2p + 2p + 2p → sp 3 + sp 3 + sp 3 + sp 3 • The type of the hybrid orbital is dependent on the type of participating atomic orbitals (For example: sp, sp 2 , sp 3 etc) Formation of ammonia 2p N Electrons from hydrogen N 2s Hybridization sp 3 sp 3 sp 3 sp 3 Formation of ammonia Formation of ammonia N H Three single bonds Three σ bonds: sp 3 (N) overlaps 1s (H) One lone-pair (N) Molecular shape: trigonal pyramidal H H Bond angle = 106.7 o From VSEPR Types of Hybrid Orbitals...
View Full Document

Page1 / 71

1.4 theories of covalent bonding ppt - Introductory...

This preview shows document pages 1 - 16. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online