Electronegativity Flashcards
What is electronegativity?
The ability of an atom to attract the bonding electrons in a covalent bond
What three things is an atom’s electronegativity affected by?
1) Nuclear Charge
2) Size of an atom
3) Location of shared pair of electrons
How is electronegativity measured?
The Pauling scale
What do large values on the Pauling scale indicate?
Atoms are very electronegative
What bond type is an electronegativity difference of 0 for?
A pure covalent bond
What bond type is an electronegativity difference of 0-1.8 for?
A polar covalent bond
What bond type is an electronegativity difference of 1.8< ?
Ionic bond
What collection of molecules have pure covalent bonds?
Diatomic molecules
Why are hydrocarbons non-polar molecules?
C and H have very similar electronegativity values so there is an even distribution of electrons
What four elements are most electronegative?
Nitrogen, Oxygen, Fluorine, Chlorine
Where are the most electronegative elements?
Furthest right and furthest up the periodic table (excluding noble gases)
What characteristic does a non-polar molecule have?
It’s molecule is symmetrical so the dipoles in either direction cancel out
What are intermolecular forces?
The forces between molecules
What is a simple molecular lattice?
Molecules held in arrangement by weak forces
What forces are the weakest?
London forces
What forces are the second weakest?
Permanent dipole-dipole interactions
What forces are the strongest?
Hydrogen bonds
What is the permanent dipole-dipole interactions between?
A partially positive charged atom of one molecule and a partially negative charged atom of another molecule
What molecule demonstrates dipole-dipole interactions?
HCl
Are London forces instantaneous?
Yes - they are always changinf
Why are London forces weak?
They are only slightly charged at any point
What do instantaneous dipoles induce in neighbouring molecules?
Induced dipoles
What two types of molecules can London forces occur between?
1) non-polar molecules
2) non-polar with permanent dipoles
How does a molecules london forces change when there is an increasing number of electrons? Why?
They increase as there are more induced dipoles
How would stronger london forces affect the boiling/ melting point?
Increases them as more energy is needed to overcome them
How is the negative charge around a covalent bond distributed?
Not evenly
How does electronegativity vary across a period?
It Increases along a period as the atomic radius decreases and charge density increases.
How does electronegativity vary down a group?
It decreases - shielding increase so atomic radius increases so charge density decreases
How can polar molecules with a permanent dipole align?
To form a lattice of molecules similar to an ionic lattice
Why do straight chain molecule’s experience stronger London forces?
They can pack closer together, reducing the distance over which the force acts, making it stronger
Why do longer alkane chains have higher boiling points?
They have a larger Mr, so stronger London forces between chains
Why does branching of alkane chains cause for weaker London forces?
The chains are less able to pack tightly together so the distance the forces act is increased and the attractive forces are weakened - lower boiling point.
What do hydrogen bonds act between? (Exclusively)
Between hydrogen and either nitrogen, oxygen or fluorine (most electronegative atoms)
How is a hydrogen bond demonstrated in a diagram?
A dotted line
Why does ice have a Lower density than liquid water?
The hydrogen bonds hold the molecules in a rigid structure with a lot of air gaps
Why are water and alcohols not good at dissolving polar molecules?
Some can’t form hydrogen bonds
