Try something like this, That wasn't the correct way to specify a Range (as you found out)

Note the colon in the .Range


Option Explicit

Sub Macro1()
    Dim L As Long
    
    L = 8
    
    Worksheets("Sheet2").Select
    ActiveSheet.Shapes.AddChart.Select
    ActiveChart.ChartType = xlXYScatter
    ActiveChart.SetSourceData Source:=Worksheets("Sheet1").Range("A1:B" & L)
End Sub