how do i validate a checkbox, the code below gives errors

error message is 

 Uncaught TypeError: "#SaC_Check".is is not a function

Ehi

2.    $("#SaC").click(function (e) {
3. 
   
4.                 if (!('#SaC_Check').is(':checked')) {
5.                     alert("Please click the checkbox to agree to our Terms & Conditions !");
6.                 };
7.             });