Lesson 3: Bonding and Electronegativity Flashcards
Hydrocarbons, electronegativity and polarity.
Organic Compounds
Description
A covalent compound that contains one or more carbon chain.
Organic Compounds: Hydrocarbons
Bond Length and Strength
- The more carbon bonds there are, the longer the chain.
- The longer the chain, the more energy required to break the bonds.
Organic Compounds: Hydrocarbons
Properties
Long chains
- Higher boiling point.
- High volatility.
- High viscosity.
- Low flammability.
Organic Compounds: Hydrocarbons
High Boiling Point
Property
- Property of long chain hydrocarbons.
- Requires a lot of energy to break the bonds between carbon atoms.
Organic Compounds: Hydrocarbons
Low Volatility
Property
- The high boiling point means the hydrocarbon has low volatility.
- Volatility is the tendency to turn into a gas.
Organic Compounds: Hydrocarbons
Viscosity
Property
- Long chains are likely to get tangled.
- This causes the substance to ‘clump together’ and flow slowly.
Organic Compounds: Hydrocarbons
Flammability
Property
- Larger chains don’t vapourise easily (low volatility).
- Ignition is much more effective if the hydrocarbon and oxygen are mixed together as gas.
Metallic Bonding
Description
- Electrons on the highest energy level of a metal atom become delocalised.
- Creates a sea of delocalised electrons and layers of positive ions.
Bonding and Electronegativity
Description
- The tendency of an atom to attract a bonding pair of electrons.
- Atoms with similar electronegativity for covalent bonds.
- Those with different electronegativity form ionic bonds.
Electronegativity and Polarity
Factors Affecting Electronegativity
- Atomic charge.
- Distance from the nucleus.
- Electron shielding.
Electronegativity and Polarity
Electron Shielding
Factors of Electronegativity
- Core electrons repelling outer electrons.
- This reduces the effect of the charge of the nucleus.
Electronegativity and Polarity
Atomic Charge
Factors of Electronegativity
- The greater the charge of the nucleus, the stronger the attraction of electrons.
Electronegativity and Polarity
Distance from Nucleus
Factors of Electronegativity
- Outer shell electrons are further from the nucleus.
- The ‘pull’ of the nucleus on those electrons is weaker because there is a greater distance and more electron shielding.
Electronegativity and Polarity
Differences in Electronegativity
- The more electronegative atom will have a greater share of electrons.
- Eg. Cl is more electronegative than H, so in HCl the electrons are pulled towards Chlorine.
- This is called a dipole, when each end of a bond has a different charge.
Electronegativity and Polarity
Differences in Electronegativity
Summary
- No difference: non-polar covalent bond.
- Small difference: polar covalent bond.
- Large difference: ionic bond.
Electronegativity and Polarity
Dipoles and Polarity
- Dipoles represent differences in electronegativity.
- If there is a difference, the molecule is polar.
- Water is a polar molecule.
Electronegativity and Polarity
Bonding in Identical Atoms
- In a covalent bond, electrons are shared.
- When two atoms are identical, electrons are shared equally.
- This is because they have the same electronegativity.
Electronegativity and Polarity
Charge Difference
- The charge difference between H and Cl is called a permanent dipole.
- HCl is non-symmetrical (polar) and therefore a polar covalent bond.
Electronegativity and Polarity
Non-polar Molecules
- Symmetrical molecules are non-polar even though they contain polar bonds.
- Eg. C-Cl4: 4 dipoles acting in opposite directions cancel each other out.
Electronegativity and Polarity
Shape and Polarity
- CH3Cl is a polar molecule as the polarity of the C-Cl bond is not cancelled out.
- in CCl4 the C-Cl bonds cancell each other out as the molecule is symmetrical.
Electronegativity and Polarity
Solubility
- Solubility depends on polarity.
- If the molecule contains polar bonds it will dissolve well in polar solvents.
- If the molecule is non-polar it will likely dissolve in non-polar solvants.
