Chem Bonding [VSEPR, electronegativity]

What is a covalent bond?

Electrostatic attraction between the shared pair of electrons and the positively charged nuclei

What is a dative covalent bond?

A covalent bond formed when the shared pair of electrons is provided by only one of the bonding atoms (donor → acceptor)

• Donor must have a lone pair of electrons

• Acceptor must have a vacant, low-lying orbital to accept the pair

How are the central and side atoms identified in dot-and-cross diagrams?

Central

• Less electronegative

• More unpaired electrons

Side

• More electronegative

• Fewer unpaired electrons

What is the order of the strength of repulsion between bond pairs?

lone pair-lone pair > lone pair-bond pair > bond pair-bond pair

2 regions of e- density, 0 lone pairs

• Electron pair geometry / Molecular geometry

• Bond angle

• Linear

• 180º

3 regions of e- density, 0 lone pairs

• Electron pair geometry / Molecular geometry

• Bond angle

• Trigonal planar

• 120º

3 regions of e- density, 1 lone pair

• Electron pair geometry

• Molecular geometry

• Bond angle

• Trigonal planar

• Bent

• <120º

4 regions of e- density, 0 lone pairs

• Electron pair geometry / Molecular geometry

• Bond angle

• Tetrahedral

• 109.5º

4 regions of e- density, 1 lone pair

• Electron pair geometry

• Molecular geometry

• Bond angle

• Tetrahedral

• Trigonal pyramidal

• ~107º

4 regions of e- density, 2 lone pairs

• Electron pair geometry

• Molecular geometry

• Bond angle

• Tetrahedral

• Bent

• ~105º

5 regions of e- density, 0 lone pairs

• Electron pair geometry / Molecular geometry

• Bond angle

• Trigonal bipyramidal

• 120º or 90º

5 regions of e- density, 1 lone pair

• Electron pair geometry

• Molecular geometry

• Bond angle

• Trigonal bipyramidal

• See-saw

• N.A.

5 regions of e- density, 2 lone pairs

• Electron pair geometry

• Molecular geometry

• Bond angle

• Trigonal bipyramidal

• T-shape

• 90º

5 regions of e- density, 3 lone pairs

• Electron pair geometry

• Molecular geometry

• Bond angle

• Trigonal bipyramidal

• Linear

• 180º

6 regions of e- density, 0 lone pairs

• Electron pair geometry / Molecular geometry

• Bond angle

• Octahedral

• 90º

6 regions of e- density, 1 lone pair

• Electron pair geometry

• Molecular geometry

• Bond angle

• Octahedral

• Square pyramidal

• <90º

6 regions of e- density, 2 lone pairs

• Electron pair geometry

• Molecular geometry

• Bond angle

• Octahedral

• Square planar

• 90º

Why do lone pairs exert greater repulsion than a bond pair?

• Lone pair is only attracted by 1 positive nucleus, hence closer to the central atom

• Bond-pair electrons are attracted by 2 nuclei

Define electronegativity of an element

A measure of the relative tendency of an atom of the element to attract the shared electron-pair in a covalent bond

What is the trend of electronegativity?

Decreases down a group, increases across a period

How does electronegativity affect bond angle?

1. X is more electronegative than Y

2. X draws bond pairs closer to itself, bringing bond pairs closer to the nucleus of X

3. Bond pair electrons of X exert more repulsion than those in Y

4. Bond angle is greater for bond pairs around X

What determines the polarity of a bond

• Greater electronegativity difference → More polar

• Overall dipole moments for molecules made of 3 or more atoms