Created by Maxie Riley over 4 years ago
Electronegitivety-bond polarity in covalent bonds
Electonegativety is the powers of an atom to attract the electron density in a covalent bond towards it's self.
When we consider the electrons as charge clouds, the term electron density is often used to describe the way the negative charge is distributed in a molecule.
The Pauling scale is used to measure electronegitivety.
The Pauling Scale
It runs from 0 to 4
The greater the number the more electronegitivety in the atom.
Electronegitivety depends on: the nuclear charge the distance between the nucleus and the outer shell of the electrons the shielding of the nuclear charge by electrons in the inner shells
Also: The smaller the atom, the smaller the atomic radius and ∴ the greater the electronegitivety the larger the nuclear charge (for a given shielding affect) the greater the electronegitivety.
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electonegitivety is a word god darn it!
AQA spec reference3.1.3
Trends in electronegetivity
As we go up a group in the periodic table the electronegitivety increases. (smaller atomic radius, less shielding. as we go across a period the electronegitivity increases. (nuclear charge increases, inner levels stay the same, atoms are smaller)
Polarity of covalent bonds
Polarity is about the unequal sharing of electrons between atoms that are bonded together covalently. it is a property of the bond.
Covalent bond between two atoms of the same species.
when both the atoms are same (such as chlorine in the diagram) the electrons in the bond must be shared equally.Both atoms have the same electonegitivety and as such are completely non-polar.
Covalent bonds between two different atoms
when two atoms of different electronegativity bond covalently they will not share electrons equaly.
Hydrogen has a electronegitivety of 2.1 and chlorine of 3.0 . This means that the electrons int he bond will be attracted to the Cl more than the hydrogen. the electron cloud is distorted towards the Cl.
this means the chlorine side is slightly more negatively chared.we show that by the following notation:
δ+H -- Clδ-
the greater the difference in electronegitivety the more polar the bond.