Electronegativity and bond polarity

What is electronegativity ?

Ability of an atom to attract the bonding electrons in a covalent bond

What causes an attraction for electrons (electronegativity)?

A positive atomic core ( atom has lost outer electrons)

What is core charge ?

The resultant of the positive charge on protons and the negative charge on the outer electrons

How do you calculate core charge ?

Charge of nucleus (protons) (-) electrons on all of the inner shells (ignore outer shell electrons ).

They cancel each other out until you are left with a charge of positive or negative and a number of charge .

What 2 factors increase electronegativity ?

1. Higher core charge .

   The group number is the core charge , but if a transition metal you have to calculate it . E.g : group 1 have a +1 core charge attracting the shared electrons.

2. Smaller size of atom . With less shells of electrons the core of the atom is closer to the shared electrons , giving it greater attraction to the shared electrons , therefore it pulls them forwards itself more

What are the 2 trends of electronegativity in the periodic table as a result of increasing electronegativity factors ?

1. Electronegativity increases from left to right across the periodic table

2. Electronegativity decreases down a group

What is the Pauling scale of electronegativity ?

What is a permanent dipole and where are they found ?

A small charge difference across a bond that results from a difference in the electronegatives of the bonded atoms .

They are in polar covalent bonds .

How does electronegativity relate to bonding type ?

What is a polar molecule?

A molecule that has an overall dipole taking into account any dipoles across the bonds .

What 2 things must a molecule have to have a permanent dipole ?

1. Difference in electronegativity between atoms in its bonds

2. Must not be totally symmetrical

What are bond dipoles ?

Dipoles across individual bonds within a molecule

What is an overall dipole ?

The dipole that can result from the addition of all the bind dipoles in a molecule

How can a molecule have no overall dipole ?

• Symmetrical molecule

• Bond dipoles cancel out

• Non-polar

How can a molecule have an overall dipole ?

• Not totally symmetrical

• Bond dipoles reinforce each other

• Molecule has a permanent dipole

• Molecule is polar

What are induced dipoles ( London forces ) and how do they happen ?

• Happen in most non-ionic substances

• Electrons are evenly distributed but always moving in a compound with little to no electronegativity

• Random movement means a dipole will form

• This will induce a dipole in neighbouring molecules

What 2 factors effect the strength of induced dipoles ?

1. Number of electrons- the more electrons, the stronger the forces are

2. Shape- The larger the surface area is, the more contact there is to transfer the dipole forces 

When does hydrogen bonding occur ?

• When there is a large difference in electronegativity

• Hydrogen bonds to nitrogen , oxygen or fluorine

What does hydrogen bonding cause and why ?

• Causes unusually high boiling points

• Causes water to be less dense than ice

• As it is the strongest type of bonding out of all of the intermolecular forces