VSEPR - 4.4

Q1: What are Lewis-Dot Structures used for?

A:
Lewis-Dot Structures are used to show how atoms share electrons in a molecule.

• The element symbol is written in the middle and surrounded by dots representing electrons.

Q2: What rules should be followed when drawing Lewis-Dot Structures?

A:

1. The least electronegative element is placed in the center.

2. All other elements surround it.

3. Count the total number of valence electrons needed.

4. If there is a charge, add or subtract electrons from the total valence count.

Q3: What is a Co-ordinate Covalent Bond?

A:
A Co-ordinate Covalent Bond is a covalent bond in which one atom contributes both electrons to the shared pair.

• This means one element forms the bond without help from the other atom.

Q4: What is an Expanded Octet?

A:
An Expanded Octet occurs when the central atom has more than 8 electrons in its valence shell.

• This happens when the d-orbital is introduced.

• The first 10 elements in the periodic table do not experience this.

Q5: What is an Incomplete Octet?

A:
An Incomplete Octet occurs when an atom has fewer than 8 electrons in its valence shell.

• Elements like Boron and Beryllium may have incomplete octets when forming covalent bonds.

Q6: What is a Resonance Structure?

A:
A Resonance Structure is one of two or more Lewis structures that show the same arrangement of atoms, but different arrangements of electron pairs.

Q7: What does VSEPR stand for and what is it used for?

A:
VSEPR stands for Valence-Shell Electron-Pair Repulsion Theory.
It is used to predict the molecular shapes of atoms and compounds based on:

• Bond length (distance between nuclei)

• Bond angle (angle between two bonded atoms)

These properties will allow us to determine what physical

and chemical properties each molecule will have

Q8: Who developed the VSEPR theory?

A:
Ronald Gillespie and Ronald Nyholm developed the VSEPR theory.

Q9: What does the VSEPR theory propose?

A:
It proposes that electron groups (single, double, triple bonds, or lone pairs) position themselves as far apart as possible to reduce repulsion, creating a specific geometric shape

Q10: How many types of electron-group arrangements exist according to VSEPR theory?

A:
There are five types of electron-group arrangements.

Q11: What happens when all the electrons around the central atom are bonding (no lone pairs)?

A:
The molecule’s molecular shape has the same name as the electron-group arrangement.

Q12: How do lone pairs affect molecular shape?

Lone pairs cause repulsive forces that change the geometry of the molecule.

Q13: What are the three types of repulsive forces between electron groups?

Q13: What are the three types of repulsive forces between electron groups?
A:

1. Bonding pair–bonding pair (BP–BP)

2. Lone pair–lone pair (LP–LP)

3. Bonding pair–lone pair (BP–LP)

Strength of repulsion: LP–LP > BP–LP > BP–BP
(BP–BP has the weakest repulsion)

Q14: How is the hybridization of the central atom determined?

A:
Once the shape is determined using VSEPR, you can predict hybridization:

• The number of bonds around the central atom determines the type of hybridization (e.g., 4 bonds → sp³).

Q15: How can molecular shape influence polarity?

A:
The shape of the molecule affects whether dipoles cancel out or not.

• Vectors are used to show direction of polarity.

• Arrows point toward the more electronegative atom.

Q16: What is a Dipole Moment?

A:
A Dipole Moment measures how polar a molecule is by looking at the direction and strength of charge separation.
It depends on electronegativity difference (ΔEN) and molecular shape.

Q17: Does having a polar bond mean the entire molecule is polar?

A:
No — even if a bond is polar, the entire molecule may still be non-polar if the dipoles cancel out.

Q18: How do you determine the dipole moment of a molecule?

A:

1. Find the electronegativity of each atom.

2. Calculate the difference in electronegativity (ΔEN).

3. Draw the molecular structure correctly.

4. Draw vectors for each bond toward the more electronegative atom.

5. Add the vectors:

   • If they cancel out, the molecule is non-polar.

   • If they don’t cancel, the molecule is polar.