What does "across a double bond" mean?

[Fighter127]

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For example let's say there is a reaction being shown. On the left side of the arrow, there is a molecular structure with a double bond. On the right side, the double bond has disappeared and from each of the carbons the double bond was initially attached to there is a Cl atom or Br atom, etc showing a total of two Br or Cl atoms. When asked what change took place, why does the answer key say two Br atoms are added across the double bond? I guess the wording just doesn't make sense to me. Does it mean that one of the bonds is being removed, creating a single bond? If anyone could explain this it would be much appreciated!

 

[exacto]

It's just a fancy way of saying, "adding elements to the molecule at the double bond site".

it might have been a radical reaction? just guessing?

 

[theyellowking]

exacto is correct. It's a term you should familiarize yourself with, since this term will appear frequently.

For example, adding H2O across an H bond usually results in one carbon (or element) gaining H, and the other gaining OH.