using for loop to replace if-then-else

Hi,

I have written the following:

If last_colnum = 5 Then
    Application.Union(Columns(1), Columns(6)).Select
    ActiveSheet.Shapes.AddChart2(240, xlXYScatterSmoothNoMarkers).Select
ElseIf last_colnum = 9 Then
    Application.Union(Columns(1), Columns(6), Columns(10)).Select
    ActiveSheet.Shapes.AddChart2(240, xlXYScatterSmoothNoMarkers).Select
ElseIf last_colnum = 13 Then
    Application.Union(Columns(1), Columns(6), Columns(10), Columns(14)).Select
    ActiveSheet.Shapes.AddChart2(240, xlXYScatterSmoothNoMarkers).Select
ElseIf last_colnum = 17 Then
    Application.Union(Columns(1), Columns(6), Columns(10), Columns(14), Columns(18)).Select
    ActiveSheet.Shapes.AddChart2(240, xlXYScatterSmoothNoMarkers).Select
...

This goes on for many more lines. Can someone pls show me how this can be converted to a for loop instead?

Thanks for any help.