© chemistry in a cup ‘david dewar’ (some images i don’t own copyright.) © chemistry in a cup...

© Chemistry in a Cup ‘David Dewar’ (some images I don’t own copyright.)© Chemistry in a Cup (some images I don’t own copyright.)

Intermediate Bonds and Bond Polarity

Unit 2.4

© Chemistry in a Cup ‘David Dewar’ (some images I don’t own copyright.)

Unit 2.4


Intermediate Bonds and Bond PolarityExplaining ElectronegativityExplaining Electronegativity

First lets look at elements from Period 1.

Li3+

Be4+

B5+

C6+

N7+

O8+

F9+

The positive number which can be seen inside nucleus is the number of protons the atom has. The blue dots around the outside are the electrons.

Looking at these atoms you can see that they all have the same electron shell but different proton numbers. Which atom do you believe to have the highest attraction for electrons?

Answer: Fluorine ....... If you didn’t get that then I shall explain..Answer: Fluorine ....... If you didn’t get that then I shall explain..


So why does Fluorine have the greatest attraction for electrons?So why does Fluorine have the greatest attraction for electrons?



Unit 2.4

F9+

There are 2 main factors which makes this atom so electronegative.

1)Has the highest proton number. 9+ was the highest out of the selection of atoms. A great positive charge means the electrons what to get even closer to the nucleus. 2)The electron shell is relatively close to the nucleus so even higher attraction. Also, as it has 1 lone electron it can bond. Unlike Neon in the same period. Neon has higher proton number and the same electron sub shell. But it can’t bond as easy so is less electronegative.

These characteristics makes Fluorine the most electronegative atom.These characteristics makes Fluorine the most electronegative atom.


Why aren’t atoms with higher proton numbers more electron negative?Why aren’t atoms with higher proton numbers more electron negative?



Unit 2.4

F9+

At first Fluorine doesn’t seem to have a very high proton number at all so you would guess that elements with much higher proton numbers would have higher electronegativity.

But well, look at another atom with similar structure in the same group as Fluorine.But well, look at another atom with similar structure in the same group as Fluorine.

Chlorine

Cl17+

Chlorine has the same amount of outer electrons as fluorine but on a different shell. The outer electrons are further away from the nucleus so attraction is lots due to the distance away from the nucleus, where all the protons are. This means chlorine is less electron negative than fluorine. Even though Chlorine has more protons distance overall makes the attraction weaker.




Unit 2.4

Looking back at what we’ve just learnt.Looking back at what we’ve just learnt.

F9+

Fluorine is the most electronegative atom in the periodic table.Its the highest due to the last electron shell is close to the nucleus. It also has a high proton number which makes electrons want to get closer to it.

Exam help Notes:Exam help Notes:

*If in an exam you asked to define what electronegativity is the answer should be:The more electronegative an atom is, the great share of electrons it will take when bonded. (We’ll be looking at this next)

*The 3 most electronegative atoms are Nitrogen, Oxygen and Fluorine. If you have polar bond questions you’ll know the elements that have the greatest effect on a molecule will be due to these atoms. Known as “F O N”




Unit 2.4

All these electronegative atoms can then create Polar Bonds and Polar Molecules.All these electronegative atoms can then create Polar Bonds and Polar Molecules.

We’ll first look at Ammonia We’ll first look at Ammonia

δ+

δ+ δ+

δ-

Here is a molecule of ammonia. Ammonia consists of 3 Hydrogen's and 1 Nitrogen.Previously we found out that Fluorine, Oxygen and Nitrogen have the highest electronegativity.From the diagram opposite you can see little symbols δ+ and δ-, these symbols mean that this atom has a slightly positive or negative charge.Nitrogen is very electronegative so takes a greater share of electrons. As electrons have an negative charge, with the Nitrogen taking more electrons on the Nitrogen becomes more negative.

As this molecule has a +ve and a –ve end this means that this molecule is polar.

There are similar molecules like this and on the next page that are not polar and you’ll learn how to determine whether a molecule is polar or not.There are similar molecules like this and on the next page that are not polar and you’ll learn how to determine whether a molecule is polar or not.




Unit 2.4

Non-Polar MoleculesNon-Polar Molecules

An example of a non-polar molecule is Carbon DioxideAn example of a non-polar molecule is Carbon Dioxide

δ- δ-δ+

Much like Ammonia, Carbon Dioxide has and but in this case what makes this molecule non-polar is that there is no positive end. For a molecule to be polar it needs to have a and at either end.If it doesn’t in this case, carbon dioxide, the molecule cannot be polar.

δ+

δ- δ+

δ-




Unit 2.4

Can you tell which is polar and what is non-polar?Can you tell which is polar and what is non-polar?

MethaneCarbon Monoxide

Hydrogen Chloride

Butanone

Non-PolarNon-Polar

PolarPolar

PolarPolar

PolarPolar

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