Improving Performance on the AP Chemistry Examination Writing is an important communication skill, one that affects a student's score on the AP Chemistry Examination. On the free-response section of the exam, students must communicate their knowledge of chemistry to the Reader through writing. Be Specific, Answer the Question Students need to make sure they answer the question asked. The whole question should be read before and then again after answering. Students should then make sure they relate their answer to the specific question asked and include chemical species in the answer. Answers need to be specific and refer to the chemical species in the question. Example: For each of the following use appropriate chemical principles to explain the observation. Include equations as appropriate. a. In areas affected by acid rain, statues and structures made of limestone (calcium carbonate) often show signs of considerable deterioration. A common answer was that an acid-base neutralization reaction occurred. No further explanation or chemical equation was given. This general answer does not address the question, does not include references to the specific chemical species (the limestone and acid rain), and does not include a chemical equation in the answer as requested. A more detailed explanation is required to receive the full two points. One point was given for indicating acid rain has a relatively high [H+], and the second point was given for indicating that calcium carbonate solid reacts with the acid rain to form gaseous carbon dioxide. Justification vs. Definitions and Trends Many questions in the free-response section of the examination require a justification of the student's answer or an observation. According to Webster's New Collegiate Dictionary, justify is defined as "to prove or show to be just, right, or reasonable," while a definition is "a statement or meaning of a word or word group." While a definition could be part of a justification answer, providing a generic definition alone is not sufficient. The justification should include reference to the species in the question. Often students use a periodic trend to justify an answer requesting the student to use chemical principles. A trend is defined in Webster's as "a line of general direction or movement." It is an observation, not a justification. Example: This question provided four statements and asked the student to use principles of atomic structure and bonding to explain each one, making sure to include references to both substances. The first statement is that the atomic radius of lithium is larger than that of beryllium. An answer containing only the trend that the atomic radius decreases as you go across the periodic table received no credit. A correct explanation addressed the larger number of protons in beryllium than lithium and stated that while the electrons of both beryllium and lithium are in the same shell, the electrons in beryllium have has a stronger attraction to the nucleus since it has more protons. Vocabulary Students need to know and to use chemical vocabulary. Students often use chemical terms inappropriately. They also will use words like "happy" to describe atoms. Atoms are inanimate objects that can't have feelings. Students who write about "happy" atoms receive no credit without further explanation as to what they mean by "happy" chemically. Students also need to distinguish common words that they use. For example, the difference between bigger and smaller versus heavier and lighter in reference to mass comparisons can cause problems. Write in Sentences A one-word justification is not sufficient. Students should write in complete thoughts and therefore sentences. The Reader is not a mind reader, and fragmented answers may not always be interpreted by the Reader as the student intended. To prevent this from occurring, students should write their thoughts in complete sentences, including a subject and verb. The subject should be stated, preferably without the use of pronouns. Students should refrain from using the word it. They often use the word it without providing the Reader with a clear reference. Therefore, they receive no points. Review Answers Proofreading and editing should be encouraged. Students should make sure they have answered the question asked. They should check to make sure their thoughts are clear and complete. Example with 3 Student Responses and Scores 6. Use the principles of atomic structure and/or chemical bonding to explain each of the following. In each part, your answer must include references to both substances. (a) The atomic radius of Li is larger than that of Be. (b) The second ionization energy of K is greater than the second ionization energy of Ca . a) 2/2 points b) 2/2 points a) ½ points because it does not address whether or not the electrons are in same shell. b) 2/2 points a) 2/2 points b) ½ points because it does not address why it is harder to remove an electron from a filled shell.