Bond polarity + Forces between molecules Flashcards
What is electronegativity?
Electronegativity as the power of an atom to attract the pair of electrons in a covalent bond.
What produces a polar bond?
The electron distribution in a covalent bond between elements with different electronegativities will be unsymmetrical.
May also cause a molecule to have a permanent dipole.
Fluorine is the most electronegative.
What affects the power of electronegativity in an atom?
Electronegativity INCREASES along a period bc the atomic radium decreases.
Electronegativity DECREASES down a group bc more shielding.
State and explain permanent dipole intermolecular forces
Permanent dipole: stronger than vdw but weaker than hydrogen bonding
2 different atoms that are bonded that have different electronegativities.
The more electronegative atom draws more negative charge towards itself and away from the other atom - delta negative and positive regions.
What is an induced dipole?
forms when the orbital around a molecule are influenced by another charged particle.
State and explain van der waals intermolecular forces.
Van der waals: the weakest
-larger the mr, the stronger the imf.
-straight chain molecules have stronger vdw than branched as they are packed closer together - it reduced the distance over the force acts.
State and explain hydrogen bonding intermolecular forces.
Hydrogen bonding: the strongest
- only forms between a hydrogen and NOF (nitrogen, oxygen and fluorine)
- h-bonding produces high melting/boiling points therefore imf influences physical properties.
Importance of hydrogen bonding in the low density of ice and the anomalous boiling points of compounds.
When water freezes, the water molecules are no longer free to move about and the hydrogen bonds hold the molecules in fixed positions.
In order to fit into this structure, the molecules are slightly less closely packed than in liquid water. This means ice is less dense than water.
EQ: Which polymer has hydrogen bonding between the polymer chains?
Answer: A
EQ: Which change occurs when water is vaporised?
Answer: C
EQ: Draw a diagram to show the strongest type of interaction between two molecules of ethanol (C2H5OH) in the liquid phase.
Include all lone pairs and partial charges in your diagram.
EQ: Which row shows the bonding in ammonium chloride?
Answer: C
EQ: Explain how permanent dipole-dipole forces arise between hydrogen
chloride molecules.
- Difference in electronegativity leads to bond polarity
- and there is an attraction between ∂+ on one molecule and ∂− on
another
The melting point of XeF4 is higher than the melting point of PF3
Explain why the melting points of these two compounds are different.
In your answer you should give the shape of each molecule, explain why each molecule has that shape and how the shape influences the forces that affect the melting point.
