MR - Electronegativity and Intermolecular Forces Flashcards

1
Q

Define electronegativity

A

The ability to attract bonding electrons in a covalent bond

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2
Q

What scale is electronegativity measured on and what do higher values mean?

A

The Pauling scale

The higher the value, the more electronegative the element is

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3
Q

State the most electronegative element

A

Fluorine

although Oxygen, Nitrogen and Chlorine are also strongly electronegative

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4
Q

Describe the trend in electronegativity across the periods

A

Electronegativity increases across the periods

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5
Q

Describe the trend in electronegativity down the groups

A

Electronegativity decreases down the groups (ignoring noble gasses)

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6
Q

Explain polarity of covalent bonds

A

In a covalent bond between two atoms of different electronegativities, the bonding electrons are pulled towards the more electronegative atom. This makes the bond polar

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7
Q

Explain why a molecule’s shape and polarity effect whether it has a permanent dipole

A
  • Simple molecules (like HCl), polar bonds give the whole molecule a permanent dipole
  • More complicated molecules may have several polar bonds. If they are arranged so they point in opposite directions, they’ll cancel each other out (non-polar overall)
  • If the polar bonds all point in roughly the same direction, then the molecule is polar
  • Lone pairs of electrons on the central atom also have an effect on the overall polarity
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8
Q

Name the 3 types of intermolecular bonds

A
  • Permanent Dipole - Permanent Dipole
  • Instantaneous Dipole - Induced Dipole
  • Hydrogen Bonding
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9
Q

Give the 3 types of intermolecular bonds in order of strength from strongest to weakest

A
  • Hydrogen
  • PD-PD
  • ID-ID
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10
Q

Describe PD-PD bonding

A

The delta + and - charges on polar molecules cause a weak electrostatic force of attraction between molecules

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11
Q

Describe ID-ID bonding

A
  • Electrons in charge cloud are always moving quickly. At one moment, the electrons in a bond are more likely to be one side than the other
  • This dipole can induce a temporary dipole in adjacent molecules. The molecules are then attracted to each other
  • Because the electrons are constantly moving, dipoles are being created and destroyed all the time.
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12
Q

Give 3 factors that effect the strength of intermolecular forces

A
  • The polarity of the molecules
  • The size of the molecule
  • The shape of the molecule (e.g. branching)
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13
Q

Describe hydrogen bonding

A
  • Hydrogen is bonded to an electronegative element drawing the bonding electrons away from Hydrogen
  • This bond is polarised so Hydrogen forms an electrostatic attraction to a lone pair of electron of other molecules
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