CHEM 150 1nd Edition Lecture 23Outline of Last Lecture • The uncertainty principle (pp 328-329) quantifies our inability to know everythingabout something as small as an electron. The act of observing them changes them.• Our perception of an electron as a wave may be due to this limit.• The electron wave occupies all of space but the electron particle must be somewhere. • The square of the wave function in an area is the probability of finding the electron in that area. We often think of the area in space where the electron spends90% of its time as the ‘shape’ of the atomic orbital.• This is how we get the orbital “pictures” in section 7.7• Main group elements form monatomic ions that have a pseudo-noble gas configuration (sn2np2).Outline of Current Lecture • Periodic trends:• Atomic radii: atoms tend to be larger as you move left and down on the periodic table.• Moving down a group, the valence shell gets farther from the nucleus• Moving right across the period: the effective nuclear charge is growing (shielding is constant but Z increases) so the valence shell is pulled closer to the nucleus.Current LectureQ: Rank the following atom in terms of increasing size: Cl, Ge, P, SnA: -Ionic size vs. atomic size-Anions are larger than the parent atom-Cations are smaller than the parent atom-The larger the charge, the greater the change in size.Q: Which is larger?Mg or Mg2+F or F-Sr2+ or Br- Q: Rank the following ions in order of increasing size (ionic radii):Ca2+, Cl-, Ga3+, K+, P3-, S2- • Ionization energy (IE)Write a chemical equation that corresponds to the first ionization energy of potassium (ÄH =IE1 )-The 1st ionization energy gets larger (more positive) as you move right or up on the periodic table.-This is the opposite of the trend in atomic radii. The smaller the atom, the closer the electron is to the nucleus and the harder it is to remove.-Note the anomalies due to the stability of filled and half-filled subshells.Q: Which has a higher IE1?Al or Si Sn or Pb N or OQ: Each subsequent electron takes more energy to remove (IE2 > IE1 ). Why?A: Q: At some point there is a huge difference in the next 1E. When does this happen with Ti? Why? • Electron Affinity (EA)-Write a chemical equa tion that corresponds to the first electron affinity of bromine. (ÄH=EA1). -The first electron affinity for an atom tends to decrease (ÄH becomes more negative) as you move right or up on the periodic table-Smaller atoms release more energy when you add an electron, because the electron gets closer to the nucleus.-Note the severe exceptions due to the stability of filled and half-filled shells.-The second (and subsequent) electron affinities are always positive. Why?Q : Which has the most negative EA1?S or Cl Br or I N or
View Full Document
Unlocking...