diff --git a/common/lib/capa/capa/chem/chemtools.py b/common/lib/capa/capa/chem/chemtools.py
index 132bde17b4..e5a8e1a6f6 100644
--- a/common/lib/capa/capa/chem/chemtools.py
+++ b/common/lib/capa/capa/chem/chemtools.py
@@ -1,5 +1,6 @@
 from collections import OrderedDict
 import json
+import unittest
 
 
 def vsepr_parse_user_answer(user_input):
@@ -16,13 +17,20 @@ def vsepr_build_correct_answer(geometry, atoms):
 
 
 def vsepr_grade(user_input, correct_answer, ignore_p_order=False, ignore_a_order=False, ignore_e_order=False):
-    """ Flags ignore_(a,p,e)_order are for checking order in axial, perepherial or equatorial positions
+    """ Flags ignore_(a,p,e)_order are for checking order in axial, perepherial or equatorial positions.
+        Allowed cases:
+            c0, a, e
+            c0, p
+        Not implemented and not tested cases when p with a or e (no need for now)
     """
     # print user_input, type(user_input)
     # print correct_answer, type(correct_answer)
     if user_input['geometry'] != correct_answer['geometry']:
         return False
 
+    if user_input['atoms']['c0'] != correct_answer['atoms']['c0']:
+        return False
+
     # not order-aware comparisons
     for ignore in [(ignore_p_order, 'p'), (ignore_e_order, 'e'), (ignore_a_order, 'a')]:
         if ignore[0]:
@@ -50,3 +58,79 @@ def vsepr_grade(user_input, correct_answer, ignore_p_order=False, ignore_a_order
                 return False
 
     return True
+
+
+class Test_Grade(unittest.TestCase):
+    ''' test grade function '''
+
+    def test_incorrect_geometry(self):
+        correct_answer = vsepr_build_correct_answer(geometry="AX4E0", atoms={"c0": "N", "p0": "H", "p1": "(ep)", "p2": "H", "p3": "H"})
+        user_answer = vsepr_parse_user_answer(u'{"geometry":"AX3E0","atoms":{"c0":"B","p0":"F","p1":"B","p2":"F"}}')
+        self.assertFalse(vsepr_grade(user_answer, correct_answer))
+
+    def test_incorrect_positions(self):
+        correct_answer = vsepr_build_correct_answer(geometry="AX4E0", atoms={"c0": "N", "p0": "H", "p1": "(ep)", "p2": "H", "p3": "H"})
+        user_answer = vsepr_parse_user_answer(u'{"geometry":"AX4E0","atoms":{"c0":"B","p0":"F","p1":"B","p2":"F"}}')
+        self.assertFalse(vsepr_grade(user_answer, correct_answer))
+
+    def test_correct_answer(self):
+        correct_answer = vsepr_build_correct_answer(geometry="AX4E0", atoms={"c0": "N", "p0": "H", "p1": "(ep)", "p2": "H", "p3": "H"})
+        user_answer = vsepr_parse_user_answer(u'{"geometry":"AX4E0","atoms":{"c0":"N","p0":"H","p1":"(ep)","p2":"H", "p3":"H"}}')
+        self.assertTrue(vsepr_grade(user_answer, correct_answer))
+
+    def test_incorrect_position_order_p(self):
+        correct_answer = vsepr_build_correct_answer(geometry="AX4E0", atoms={"c0": "N", "p0": "H", "p1": "(ep)", "p2": "H", "p3": "H"})
+        user_answer = vsepr_parse_user_answer(u'{"geometry":"AX4E0","atoms":{"c0":"N","p0":"H","p1":"H","p2":"(ep)", "p3":"H"}}')
+        self.assertFalse(vsepr_grade(user_answer, correct_answer))
+
+    def test_correct_position_order_with_ignore_p_order(self):
+        correct_answer = vsepr_build_correct_answer(geometry="AX4E0", atoms={"c0": "N", "p0": "H", "p1": "(ep)", "p2": "H", "p3": "H"})
+        user_answer = vsepr_parse_user_answer(u'{"geometry":"AX4E0","atoms":{"c0":"N","p0":"H","p1":"H","p2":"(ep)", "p3":"H"}}')
+        self.assertTrue(vsepr_grade(user_answer, correct_answer, ignore_p_order=True))
+
+    def test_incorrect_position_order_ae(self):
+        correct_answer = vsepr_build_correct_answer(geometry="AX6E0", atoms={"c0": "Br", "a0": "test", "a1": "(ep)", "e0": "H", "e1": "H", "e2": "(ep)", "e3": "(ep)"})
+        user_answer = vsepr_parse_user_answer(u'{"geometry":"AX6E0","atoms":{"c0":"Br","a0":"test","a1":"(ep)","e0":"H","e1":"(ep)","e2":"(ep)","e3":"(ep)"}}')
+        self.assertFalse(vsepr_grade(user_answer, correct_answer))
+
+    def test_correct_position_order_with_ignore_a_order_not_e(self):
+        correct_answer = vsepr_build_correct_answer(geometry="AX6E0", atoms={"c0": "Br", "a0": "(ep)", "a1": "test", "e0": "H", "e1": "H", "e2": "(ep)", "e3": "(ep)"})
+        user_answer = vsepr_parse_user_answer(u'{"geometry":"AX6E0","atoms":{"c0":"Br","a0":"test","a1":"(ep)","e0":"H","e1":"H","e2":"(ep)","e3":"(ep)"}}')
+        self.assertTrue(vsepr_grade(user_answer, correct_answer, ignore_a_order=True))
+
+    def test_incorrect_position_order_with_ignore_a_order_not_e(self):
+        correct_answer = vsepr_build_correct_answer(geometry="AX6E0", atoms={"c0": "Br", "a0": "(ep)", "a1": "test", "e0": "H", "e1": "H", "e2": "H", "e3": "(ep)"})
+        user_answer = vsepr_parse_user_answer(u'{"geometry":"AX6E0","atoms":{"c0":"Br","a0":"test","a1":"(ep)","e0":"H","e1":"H","e2":"(ep)","e3":"H"}}')
+        self.assertFalse(vsepr_grade(user_answer, correct_answer, ignore_a_order=True))
+
+    def test_correct_position_order_with_ignore_e_order_not_a(self):
+        correct_answer = vsepr_build_correct_answer(geometry="AX6E0", atoms={"c0": "Br", "a0": "(ep)", "a1": "test", "e0": "H", "e1": "H", "e2": "H", "e3": "(ep)"})
+        user_answer = vsepr_parse_user_answer(u'{"geometry":"AX6E0","atoms":{"c0":"Br","a0":"(ep)","a1":"test","e0":"H","e1":"H","e2":"(ep)","e3":"H"}}')
+        self.assertTrue(vsepr_grade(user_answer, correct_answer, ignore_e_order=True))
+
+    def test_incorrect_position_order_with_ignore_e_order__not_a(self):
+        correct_answer = vsepr_build_correct_answer(geometry="AX6E0", atoms={"c0": "Br", "a0": "(ep)", "a1": "test", "e0": "H", "e1": "H", "e2": "H", "e3": "(ep)"})
+        user_answer = vsepr_parse_user_answer(u'{"geometry":"AX6E0","atoms":{"c0":"Br","a0":"test","a1":"(ep)","e0":"H","e1":"H","e2":"(ep)","e3":"H"}}')
+        self.assertFalse(vsepr_grade(user_answer, correct_answer, ignore_e_order=True))
+
+    def test_correct_position_order_with_ignore_ae_order(self):
+        correct_answer = vsepr_build_correct_answer(geometry="AX6E0", atoms={"c0": "Br", "a0": "(ep)", "a1": "test", "e0": "H", "e1": "H", "e2": "H", "e3": "(ep)"})
+        user_answer = vsepr_parse_user_answer(u'{"geometry":"AX6E0","atoms":{"c0":"Br","a0":"test","a1":"(ep)","e0":"H","e1":"H","e2":"(ep)","e3":"H"}}')
+        self.assertTrue(vsepr_grade(user_answer, correct_answer, ignore_e_order=True, ignore_a_order=True))
+
+    def test_incorrect_c0(self):
+        correct_answer = vsepr_build_correct_answer(geometry="AX6E0", atoms={"c0": "Br", "a0": "(ep)", "a1": "test", "e0": "H", "e1": "H", "e2": "H", "e3": "(ep)"})
+        user_answer = vsepr_parse_user_answer(u'{"geometry":"AX6E0","atoms":{"c0":"H","a0":"test","a1":"(ep)","e0":"H","e1":"H","e2":"(ep)","e3":"H"}}')
+        self.assertFalse(vsepr_grade(user_answer, correct_answer, ignore_e_order=True, ignore_a_order=True))
+
+
+def suite():
+
+    testcases = [Test_Grade]
+    suites = []
+    for testcase in testcases:
+        suites.append(unittest.TestLoader().loadTestsFromTestCase(testcase))
+    return unittest.TestSuite(suites)
+
+if __name__ == "__main__":
+    unittest.TextTestRunner(verbosity=2).run(suite())