Partial load

Partial charge of the water molecule.

Polarity of chloromethane (left) and the Grignard compound methyl magnesium chloride with details of the partial charges.

Under partial charge (lat. Pars therefore "part", whether partial charge ), also partial charge , refers to the different charge of two binding partners ( atoms or molecular moieties ). They occur through polar atomic bonds . The charges are indicated in chemical formulas with δ− and δ + above the element symbol.

If the binding partners of an atomic bond differ in their electronegativity , the distribution of the binding electrons is no longer uniform, but polarization (different charge of the partners) occurs, which is caused by the shift of the charge carriers ( electrons ). This electron shift causes the binding partners to be partially (= partially) positively and negatively charged. The partial charge in an XY bond can be estimated using the following formula: ${\ displaystyle S_ {X} = G_ {X} -N_ {X} -B_ {X} \ cdot {\ frac {\ chi _ {X}} {\ chi _ {X} + \ chi _ {Y}} }}$

It stands for the group number of the element , is the number of electrons not involved in the bond from the atom , is the number of electrons that are involved in the bond and or is the electronegativity values of or . For example, for the molecule HF: and , F is partially negative and H partially positively charged. ${\ displaystyle G_ {X}}$ ${\ displaystyle X}$ ${\ displaystyle N_ {X}}$ ${\ displaystyle X}$ ${\ displaystyle B_ {X}}$ ${\ displaystyle \ chi _ {X}}$ ${\ displaystyle \ chi _ {Y}}$ ${\ displaystyle X}$ ${\ displaystyle Y}$ ${\ displaystyle S_ {F} = - 0 {,} 29}$ ${\ displaystyle S_ {H} = 0 {,} 29}$

The greater the electronegativity difference (ΔEN), the greater the degree of polarization and thus the formation of the partial charges. Since binding forces arise between different charges, these become greater the greater the charge difference. Above a certain size of the difference one speaks of an ionic bond and ions .

Individual evidence

↑ ^a ^b ^c Harald Gärtner: Chemistry: formulas, laws and technical terms . Compact, 2009, ISBN 978-3-8174-7892-7 ( page 178 in the Google book search).
↑ David Clark: General chemistry: pearls of wisdom . Jones & Bartlett Pub, 2004, ISBN 978-1-890369-22-4 ( page 96 in Google Book Search).

[Gärtner-1] Harald Gärtner: Chemistry: formulas, laws and technical terms . Compact, 2009, ISBN 978-3-8174-7892-7 ( page 178 in the Google book search).

[clarc-2] David Clark: General chemistry: pearls of wisdom . Jones & Bartlett Pub, 2004, ISBN 978-1-890369-22-4 ( page 96 in Google Book Search).