Box and Whisker Formatting

I’m trying to make a box and whisker plot with log(concentration) on the y-axis for the measurement of various compounds. I want to have a group of three bars then a gap followed by another group of 3 and gap….etc. Each group of three represents one type of data point (the particular compound being measured) and then each bar is a different sampling site. I have not been able to figure out the best way to format this in Excel and make it readable. Can anyone help with this? When I enter the raw data and create a blank “Gap” series, the plot is very small and not scaled well.