6.2 Electronegativity and polarity Flashcards
In a covalent bond, where is the attraction between?
there is attraction between the nucleus of each atom & the electron being shared
- when two atoms of the same element are bonded, each atom will attract electrons shared equally
-when different atoms are bonded, one may attract an electron more strongly (more electro negative)
Define ‘electronegativity’
the attraction of a bonded atom for the pair of electrons in a covalent bond
The higher its electronegativity, the more an element attracts electrons.
What factors affect electronegativity and define them
Nuclear charge: the total charge in the nucleus for all the protons
Atomic radius: total distance from the nucleus of an atom to the outermost electron of its orbital
How does atomic radius affect electronegativity
Elements towards the right of the Periodic Table have SMALLER atomic radii, and GREATER electronegativity because of increased atomic number….the most electronegative elements are fluorine and oxygen, to the right of the Table.
How does nuclear charge affect electronegativity
Electronegativity increases when effective nuclear charge increases.
If there is a greater effective nuclear charge, there will be a greater attraction, & so a greater electronegativity.
If there are a lot of shielding electrons, outer electrons won’t be drawn towards the nucleus due to the low effective nuclear charge, and so electronegativity will be low.
What is the shielding effect
Shielding electrons are the electrons in shells closer to the nucleus than the electron you’re interested in.
Because they are all negative, if you have a lot of electrons between one electron and the nucleus, the one electron will be repelled by the electrons as well as attracted by the nucleus, which will cancel out, and there will not be a great effective nuclear force.
Pauling electronegativity scale
based on an empirical relation between the energy of a bond and the electronegativity of bonded atoms.
-non-metals typically contain the most electronegative atoms whilst group 1 metals have the least electronegative atoms
How does the ‘Pauling electronegativity scale’ work
As the pauling values increase, so does the electronegativity of the element
- highest value is 4.0 fluorine
- From left to right and bottom to top. the electronegativity increases
How to tell the bond type based on electronegativity difference?
A covalent bond has 0 electronegativity
Polar covalent 0 < x <1.8
ionic more than 1.8
What are non-polar bonds?
when the bonded electron pair is shared equally between the bonded atoms, only if:
- the bonded atoms are the same, or
- the bonded atoms have the same or similar electronegativity (less than 0.5 difference)
Pure covalent bonds
molecules of elements such as hydrogen, oxygen and chlorine come from the same element (diatomic molecules)
What are polar bonds?
when bonds are significantly different in electronegativity, they are considered to be polar, resulting in a polar bond
- polar bonds have a dipole
What is a dipole? What is a permanent dipole?
A bond or molecule whose ends have opposite charges
permanent: a dipole that does not change
Explain how to deduce and draw a polarised molecule
HCL (H=2.1 CL=3 SO ELEC DIFF=0.9)
Since chlorine is more electronegative, the bonded pair is attracted more towards it
- H-CL is polarised with a small positive charge on hydrogen and a small partial negative charge on chlorine
- H-CL with an arrow pointing towards the chlorine
More/ less electronegative element will?
More electronegative= slightly negative charge
Less electronegative= slightly positive charge
