The big difference between
Scotch and
Irish single malt whisky is the
distilling phase which is made twice with scotch and three times with Irish. This gives each other special taste and noticeable lightness with Irish one.
Also the way how malts are dried is different. Scotch is dried with smoke which logically gives the usual scotch aroma to whisky. Irish is dried with pure air and therefore there is not any kind of smoke flavour.