10 second "ALTER TABLE ALTER COLUMN" question

New to SQL2012, need help on simple sql question

 
///////////////////////////////////////////////////////////////////////////////////////////
--The following code runs and no error

alter table  TestTable2Delet
  ALTER COLUMN  FirstName varchar(25) Not Null



//////////////////////////////////////////////////////////////////////////////////////////////
--The following code don't run, ?????WHY????? Does it mean I have to have a "alter table" sentence for each alter column line??????????????

alter table  TestTable2Delet
  ALTER COLUMN  FirstName varchar(25) Not Null,  
  ALTER COLUMN  LastName  varchar(25) Not null


---?????WHY????? Does it mean I have to have a "alter table" sentence for each alter column line??????????????