1) Don’t state that p electrons are farther away from the nucleus. 1) A drop in IE occurs between groups II and III because the p electrons do not penetrate the nuclear region as greatly as s electrons do and are therefore not as tightly held. Don’t think that the trends are without anomalies. You will not earn points Exceptions occur between groups II and III and V and VI. Don’t simply stating that ionization energy increases from left to right across a period. Ionization energy increases as atomic number increases in any given period DO DON’T Effective nuclear charge, Zeff, increases the attraction of the nucleus and therefore holds the electrons more tightly. an isolated one, not part of a solid, liquid or a molecule. The Do’s and Don’ts of Periodic Trends Name_Per_ Ionization energy refers to the energy needed to remove an electron from a gaseous atom or ion, i.e. Only full energy levels, not full sublevels, are of concern in a shielding argument. Don’t use shielding for explanations across a period. Full energy levels provide some shielding between the nucleus and valence electrons. You must not simply saying that radii increase down a column. Atomic radii increase as atomic number increases down a column or group DO DON’T Increased number of energy levels (n) increases the distance over which the nucleus must attract and therefore reduces the attraction for electrons. Don’t simply stating that atomic radii decrease from left to right across a period. Atomic radii decrease as atomic numbers increase in any given period DO DON’T Effective nuclear charge, Zeff, increases the attraction of the nucleus and therefore pulls the electron cloud closer to the nucleus resulting in a smaller atomic radius. It is influenced by the nuclear pull and the number of energy levels. Atomic radius refers to the distance between the nucleus and the outer edge of the electron cloud. 2) Use increased distance (greater value of n) to justify trends down a group. Trends in the Periodic Table Justifying all of the trends on the periodic table can be simplified using these two generalizations: 1) Use Zeff to justify trends across a period. Emphasize the energy of attractions and repulsions in your explanations. Fattractionα (q+ )(q− ) d 2 or F = k (q + )(q− ) d 2 Chemistry is often defined as “the study of matter and energy”. Coulomb’s Law shows that the force of attraction between two oppositely charged particles is directly proportional to the magnitude of the charges and inversely proportional to the distance between those charges. The concept of Coulomb’s Law is important and you should mention it when appropriate in your explanations. Answers to these questions should always include a statement about how this attraction is affected. Almost all of the properties that are asked about in exam questions rely on the Coulombic (electrostatic) attraction between the outer electrons and the nucleus. Addressing one and leaving the other as implied does not usually earn the point for this type of question. In addition to discussing forces, you must mention BOTH of the atoms or ions that are in the question when stating your answer. If needed, chant over and over again, “A trend is an observation, not an explanation!” It is fine to state the trend in your answer, but you must also go further by explaining what causes the observed trend. Your must address the forces that create the trend and avoid the impulse to simply use the location on the table as an explanation of the observed property. A statement such as “In terms of atomic structure, explain why the first ionization energy of selenium is less than that of bromine.” Often these questions are not well answered because students simply state the trend, such as “ionization energy increases as you move left in a period,” and fail to address the forces at work that created the trend in the first place. Download AP Chem Periodic Trends and more Chemistry Lecture notes in PDF only on Docsity!The AP® Chemistry test typically addresses periodic trends in the free response questions.
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