Which is electronegative OH or Cl

 

A special important periodic property is electronegativity (EN).

Linus Pauling has the behavior of elements to attract electrons in compounds, with a numerical value EN Are defined. In addition to his tabular values, there are also more recent figures from Alfred and Rochow. The qualitative behavior is identical in both EN scales.

The element with the greatest electronegativity fluorine became the value EN = 4 given. Fluorine is the "ultimate electron robber" that attracts electrons in compounds from all other elements. The electropositive element lithium became the value EN = 1 given.
The trend is: EN decreases in main groups from right to left and from top to bottom. Cesium EN = 0.7 is the most electropositive. A mnemonic for the most electronegative elements is "FONCL" for the order F .. O .. N .. Cl.
{In subgroups, all elements are electropositive with EN from approx. 1 to 1.8.}

EN values ​​up to chlorine according to Pauling (without noble gases)

H

 

2,1

Li

Be

B.

C.

N

O

F.

1,0

1,5

2,0

2,5

3,0

3,5

4,0

N / A

Mg

Al

Si

P

S.

Cl

0,9

1,2

1,5

1,8

2,1

2,5

3,0

The numerical values ​​EN can be used to estimatewhether a compound has a salt-like structure with ions or a molecular structure with atomic bonds: If there is a difference ΔEN of approx. 2 or more, salts and an ionic bond are to be expected. Examples:

  • N / A EN = 0.9; Cl EN = 3.0; ΔEN = 2.1: NaCl = Salt from Na+ Cl-
  • Approx EN = 1.0; O EN = 3.5; ΔEN = 2.5: CaO = Salt from approx2+ O2-
  • H EN = 2.1; O EN = 3.5; ΔEN = 1.4: H2O = Molecule in which the bond is polar
    (the electrons are more attracted to oxygen).

question: We expect for carbon according to this concept ionically structured compounds? - C (EN = 2.5).

  • To the most electronegative element F. (EN = 4) is ΔEN = 1.5. CF4 should be (and is) a polar molecule.
  • To H (EN = 2.1) is ΔEN = 0.4. CH compounds are molecules with very low polarity.
  • Could with Al (EN = 1.5) so ΔEN = 2.0 ions occur? YES. In fact, Al4C.3 from ions Al3+ and C4- built up!

warning before overestimating the "general rules": numerical values ​​should not be used for quantitative calculations, but only for qualitative considerations. (Is it more likely a molecule or an ionic compound? Is a bond polar? Which valencies are most likely?)

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