trends of the periodic table class #5 electronegativity
TRANSCRIPT
Trends of the Periodic Table Class #5
Electronegativity
Electronegativity the idea that generated a Nobel
Prize for Dr. Linus Pauling
This guy is the ONLY person ever to win 2 Nobel Prizes by himself. Some others shared two prizes, but, he’s really the man.
Electronegativity is defined as the tendency to gain an electron in a bonding situation.
Bonding is a very complicated matter. There’s all kinds of bonds: covalent between 2 or more nonmetals, ionic bonds form between ions, metallic bonds form between atoms of metals that are stuck together, there are at least 3 kinds of intermolecular bonds, and some other odd ball ones too (resonance bonds, hybrid bonds, etc.)
Dr. Pauling measured how fairly two atoms could be expected to share electrons when bonding.
YOU ME
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2 identical atoms, like the HONClBrIF twins, will of course share their electrons perfectly, because as much as one hydrogen “wants” that electron from his partner, the desire to gain an electron in a bonding situation is equal for both.
Hydrogen has an electronegativity value of 2.1
No units! (finally!)
Each hydrogen in H2 has the same electronegativity value, so there is no difference. No difference means that each shares nicey-nice. (not like me and you and the cherry pie ala mode!)
Let’s look at HCl next.
H-ClHydrogen and chlorine “fit” together in a 1:1 ratio. Both the hydrogen and the chlorine “want” to fill up their orbitals by sharing electrons together as they covalently bond.
Look at their electronegativity values.
There’s a huge difference between them!
The greater the difference the less they share evenly.
The atom with the higher electronegativity value will “get” the electron in the bond more of the time. The greater the difference in EN values, the greater mismatch, or greater time one atom takes the electron more.
2.1 3.2
Difference is1.1
In this case, chlorine will have a full third orbital most of the time, and
hydrogen will have a full single orbital sometimes.
What is the group trend for electronegativity value in group 2 and group 17?
Group 1
Atoms
Group 1 electronegativity
values
Li
Na
K
Rb
Group 17
Atoms
Group 17 electronegativity
values
F
Cl
Br
I
State the group trend for electronegativity values below.
What is the group trend for electronegativity value in group 2 and group 17?
Group 1
Atoms
Group 1 electronegativity
values
Li 1.0
Na 0.9
K 0.8
Rb 0.8
Group 17
Atoms
Group 17 electronegativity
values
F 4.0
Cl 3.2
Br 3.0
I 2.7
The group trend for electronegativity value is decreasing.
The reason for this is that electrons would be added into the outermost (valence) orbital, which is always further and further from the nucleus as you add orbitals going down a group.
Determine the Period Trend for Electronegativity Values.
Period 2 atoms Li Be B C N O F Ne
Electro-negativity
values
State the period trend for electronegativity values, then
Explain neon’s electronegativity value???
Determine the Period Trend for Electronegativity Values.
Period 2 atoms Li Be B C N O F Ne
Electro-negativity
values1.0 1.6 2.0 2.6 3.0 3.4 4.0 ---
The period trend for electronegativity is increasing.
As you go across the table, atoms become more likely to “take” an electron in a bonding situation.
Neon: Neon, and the noble gases do not make bonds, they don’t have electronegativity values…
Relative scales and arbitrary scales… (Dr. Linus was a fun guy, and not a fungi)A relative scale is one that compares all members of the group to one set standard.
Electronegativity is a relative scale, all atoms being relative to fluorine. Dr. Pauling deterined that fluorine has the greatest tendency to gain electrons in a bonding situation.
An arbitrary scale is one that uses numbers that don’t really matter. Dr. Pauling choose 4.0 for his highest value, given only to fluorine. All other values ranged down to zero.
He could have use 100 as his top value, or eleven, or even 19.34. He picked it for his own reason. There are not 4.0 somethings, in fact there is not even a unit here.
Electronegativity is both a relative scale, and it’s an arbitrary one as well.