What is meant by electronegative gas?

[Manoj Sahu]

Today, one of my professor was teaching about Circuit Breaker and he explained about SF6 circuit breaker. He told us that SF6 is electronegative gas. But i really didn't understand what is electronegative gas. Please can someone explain in detail. Thanks in advance.!

 

[Drakkith]

From wikipedia's article on SF6 Circuit Breakers:

Current interruption in a high-voltage circuit breaker is obtained by separating two contacts in a medium, such as sulfur hexafluoride (SF6), having excellent dielectric and arc-quenching properties. After contact separation, current is carried through an arc and is interrupted when this arc is cooled by a gas blast of sufficient intensity.

The sulfur hexaflouride gas (SF6) is an electronegative gas and has a strong tendency to absorb free electrons. The contacts of the breaker are opened in a high pressure flow of sulphur hexaflouride gas and an arc is struck between them. The gas captures the conducting free electrons in the arc to form relatively immobile negative ions. This loss of conducting electrons in the arc quickly builds up enough insulation strength to extinguish the arc.

It looks to me like an electronegative gas is one which has a high tendency of absorbing a free electron to form an anion. SF6 has six atoms of fluorine, the most electronegative element, after all.