Podcast
Questions and Answers
How does the number of electron pairs around the central atom determine the shape of a molecule?
How does the number of electron pairs around the central atom determine the shape of a molecule?
Each electron pair naturally repels each other so that the largest bond angle possible exists between the covalent bonds, determining the molecule's shape.
How do lone pairs affect the bond angle in a molecule?
How do lone pairs affect the bond angle in a molecule?
Lone pairs provide additional repulsive forces, reducing the bond angle between covalent bonds by 2.5 degrees for each lone pair present.
What is the relationship between electronegativity and bond polarity?
What is the relationship between electronegativity and bond polarity?
Electronegativity is the ability of an atom to attract electrons in a chemical bond. The greater the difference in electronegativity between atoms, the more polar the bond.
How does the shape of a molecule impact its polarity?
How does the shape of a molecule impact its polarity?
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Explain how permanent dipole moments contribute to the polarity of molecules.
Explain how permanent dipole moments contribute to the polarity of molecules.
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Study Notes
Intermolecular Forces
- There are three main types of intermolecular forces, differing in strength and the molecules they act between.
- Van der Waals forces are the weakest type of intermolecular force, acting as an induced dipole between molecules.
- The strength of van der Waals forces varies depending on the molecular mass (Mr) and shape of the molecule.
- Larger molecules with a higher Mr have stronger intermolecular forces.
- Straight chain molecules experience stronger van der Waals forces than branched chain molecules due to their ability to pack closer together.
- This reduces the distance over which the force acts, making them stronger.
Permanent Dipole
- Permanent dipole forces act between molecules with a polar bond.
- The ∂+ and ∂- regions of the molecules attract each other, holding them together in a lattice-like structure.
Hydrogen Bonding
- Hydrogen bonding is the strongest type of intermolecular force.
- Hydrogen bonds only form between hydrogen and the three most electronegative atoms: nitrogen, oxygen, and fluorine.
Bond Polarity
- The negative charge around a covalent bond is not evenly spread around the orbitals of the bonded atoms.
- Electronegativity is the power of an atom to attract negative charge towards itself within a covalent bond.
- Electronegativity increases along a period as atomic radius decreases and decreases down a group as shielding increases.
- A permanent dipole forms when the two atoms bonded have different electronegativities, resulting in a polar bond.
Shapes of Molecules
- The shape of a molecule is determined by the number of electron pairs around the central atom.
- Each electron pair naturally repels each other, resulting in the largest bond angle possible between covalent bonds.
- Lone pairs present around the central atom provide additional repulsive forces, changing the bond angle.
- For every lone pair present, the bond angle between covalent bonds is reduced by 2.5°.
- The shape of a molecule can be determined by considering the type and quantity of electron pairs.
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Description
Learn about how polar molecules can align to form a lattice similar to an ionic lattice, and how induced dipoles are created when electron orbitals are influenced by charged particles. Explore the three main types of intermolecular forces and how they differ in strength and the substances they act between.
