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Electronegativity

Electronegativity is a measure of how strongly an atom pulls a shared electron pair towards it. The table below shows the electronegativities (obtained from www.thecatalyst.org/electabl.html) of a number of elements:

Table of electronegativities for selected elements
Element Electronegativity
Hydrogen (H) 2.1
Sodium (Na) 0.9
Magnesium (Mg) 1.2
Calcium (Ca) 1.0
Chlorine (Cl) 3.0
Bromine (Br) 2.8
Electronegativity

Electronegativity is a chemical property which describes the power of an atom to attract electrons towards itself.

The greater the electronegativity of an element, the stronger its attractive pull on electrons. For example, in a molecule of hydrogen bromide (HBr), the electronegativity of bromine (2.8) is higher than that of hydrogen (2.1), and so the shared electrons will spend more of their time closer to the bromine atom. Bromine will have a slightly negative charge, and hydrogen will have a slightly positive charge. In a molecule like hydrogen ( H 2 ) where the electronegativities of the atoms in the molecule are the same, both atoms have a neutral charge.

Interesting fact

The concept of electronegativity was introduced by Linus Pauling in 1932, and this became very useful in predicting the nature of bonds between atoms in molecules. In 1939, he published a book called 'The Nature of the Chemical Bond', which became one of the most influential chemistry books ever published. For this work, Pauling was awarded the Nobel Prize in Chemistry in 1954. He also received the Nobel Peace Prize in 1962 for his campaign against above-ground nuclear testing.

Non-polar and polar covalent bonds

Electronegativity can be used to explain the difference between two types of covalent bonds. Non-polar covalent bonds occur between two identical non-metal atoms, e.g. H 2 , Cl 2 and O 2 . Because the two atoms have the same electronegativity, the electron pair in the covalentbond is shared equally between them. However, if two different non-metal atoms bond then the shared electron pair will be pulled morestrongly by the atom with the highest electronegativity. As a result, a polar covalent bond is formed where one atom will have a slightly negative charge and the other a slightly positive charge. This is represented using the symbols δ + (slightly positive) and δ - (slightly negative). So, in a molecule such as hydrogen chloride (HCl), hydrogen is H δ + and chlorine is C l δ - .

Polar molecules

Some molecules with polar covalent bonds are polar molecules , e.g. H 2 O. But not all molecules with polar covalent bonds are polar. An example is C O 2 . Although C O 2 has two polar covalent bonds (between C δ + atom and the two O δ - atoms), the molecule itself is not polar. The reason is that CO 2 is a linear molecule and is therefore symmetrical. So there is no difference in charge between the two endsof the molecule. The polarity of molecules affects properties such as solubility , melting points and boiling points .

Polar and non-polar molecules

A polar molecule is one that has one end with a slightly positive charge, and one end with a slightly negative charge. A non-polar molecule is one where the charge is equally spread across the molecule.

Questions & Answers

states the Newton's second law of motion
Shallin Reply
In words it says:" when a net force is applied to an object of mass, It accelerates in the direction of the net force. The acceleration is directly proportional to the net force and inversely proportional to the mass".
Buhle
And in symbols: Fnet = ma
Buhle
thank you
Shallin
pleasure
Buhle
how does hydrogen bonds differ from London force
Madzivha Reply
how come the resultant force is 0
Andrew Reply
It's when you have equivalent forces going different directions then your resultant will be equal to zero
Temosho
describe what john's experiment proves about water molecules?
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Newton's first law of motion
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hy
Madzivha
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Ayah
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Precious
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Dire
An unknown gas has pressure,volume and temprature of 0.9atm,and 120°C.how many moles of gas are present?
Chrislyn Reply
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Bradley Reply
What is selmon
heath Reply
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how to calculate acceleration
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It depends
Mbongeni
Please state the Newton third low
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hy
Nelito
Newton's Third law states that to every force applied, there's an equal but opposite reaction
Lala
difference between a head and tail methods
Zenande Reply
difference between a head-to-tail and tail-to-tail
Zenande
head to tail you draw each vector starting head of the previous vector and tail to tail you construct a parallelogram whereas you started the two vectors from the same axis(from their tails)and the diagonal between the vectors is the resultant vector,tail to tail only includes two vectors
Mbongeni
what is a normal force
Zenande Reply
a normal force is the force that the surface applies on the object. The force is perpendicular to the surface.
Minaa
Lewis structure for C2H2
Mthokozisi Reply
H-C-H
Koketso
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Source:  OpenStax, Siyavula textbooks: grade 11 physical science. OpenStax CNX. Jul 29, 2011 Download for free at http://cnx.org/content/col11241/1.2
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