Chem 1320 1st EditionExam # 3 Study Guide Lectures: 23-33Lecture 23 (March 30)I. Periodic PropertiesYou can use the periodic table as a reference tool. It can show you the amount of electrons. There are two different types, core electrons and valence electrons. Core electrons are typically found in completely filled shells with lower principal quantum numbers, and typically do not participate in chemical reactions. Valence electrons are typically found in partially fluid filled shells that have higher principal quantum numbers, and also participate in chemical reactions. II. ConfigurationsValence electrons and their behavior are closely related to chemical properties of an element. The periodic table is organized to reflect patterns and trends in chemical properties. Effective nuclear charge and orbital size are tied to principal quantum numbers. Zeff is the shielding constant. z is the number of protons and ∂ which is the shielding constant. There is an attractions to the nucleus which uses the equation F=k(Q1Q2/ r) the Q’s stand for the charges and the r is the radius. The orbital size matters it tells you where the valence electron is. The further away it is, the less attracted to the nucleus it is. There are also things called “shielding” or “screening.” The core electrons present the valence electrons from experiencing the full positive charge on the nucleus. Zeff < z. The Zeff is influenced by the shielding constant but the interaction also depends on the distance of the electron from the nucleus. As Z goes up, so goesthe Zeff. The strength of E between the nucleus and the electron goes up. Lecture 24 (April 1) I. Orbital EnergiesThis explains why some electrons experience more attraction to the nucleus when in certain orbitals. 4s electrons can get closer to the nucleus which lowers the energy. The 2s orbitals are lower in energy. An electron in the 2s orbital can get closer to the positive charge on the nucleus. II. Ionization EnergiesThis describes the potentials or how tightly the outer electron is held. It is the minimum energy needed to remove an electron from an atom in the gas phase with its’ electrons in the ground state. I stands for ionization energy. The general trend is that I < I2 < I3… Ionization energy tends to increase when Zeff also increases when the attraction between the nucleus and remainingelectrons increase. Zeff in principal decreases because the interaction goes down because of shielding and increased distance from the nucleus. The trend in I1 increases from left to right on the periodic table and also an increase going from the bottom of a column to the top. Zeff increases left to right and bottom to top. This is due to smaller orbital size and less shielding. Removing additional electrons requires more energy, removing electrons reduces electron- electron repulsion which causes the nucleus to hold the remaining electrons more tightly Lecture 25 (April 3)I. Electron Affinity (EA)This is always a positive number. It defines a reaction and is the amount of energy released when an element picks up another electron. The general trend is that it follows the same trend as ionization energy and Zeff principal. EA increases from left to right and from bottom to top. II. Atomic RadiusThis is the size that is half the distance between two adjacent atomic nuclei that are either metal atoms or diatomic molecules. The general trend is that atomic radii follow a decreasing size trend from left to right along a period and an increasing trend going from top to bottom. The more tightly the electrons are held, the smaller the overall size of the atom. III. Metallic CharacterThere are chemical and physical properties associated with metals. The more metallic it is, the more it acts like a metal. The chemical characteristics is that they tend to have fewer valence electrons in groups one and two on the periodic table. This means they also have a tendency to form cations. The physical characteristics is that they are good conductors of heat and electricity. They have a shiny luster and are easily shaped into other forms. They can be malleable and flatten into sheets. Lastly, they have ductility and can be pulled into a wire. The general trend is that elements with a weaker Zeff tend to be more metallic because of the valence electrons are not held tightly. There is a tendency with the main group elements to gainor lose electrons to become isoelectronic with a noble gas. Lecture 26 (April 6)I. Ion SizesThese are related to the number of valence electrons and are different than atomic radii due to losing or gaining electrons. Pairing an electron causes repulsion. Adding an electron increases the size of an element and losing electrons makes the ion smaller. Anions are larger but decrease in size with an increase in Zeff.II. Role of Atomic Radii in Ion ChannelsThese are gates that regulate ion flow and are important for causing gradients in ion concentration. They are prevalent in nerve cells, neurons. They are necessary for rapid electricalsignaling in these cells. They are selective for a certain ion size dependent of the gates. III. Sodium ChannelsThese are selective for sodium even in the presence of potassium ions. Sodium channels are toosmall by design to accommodate a the larger potassium. IV. Potassium ChannelsSelective for cations because inside the channel it is lined with oxygen atoms with partial negative charges. The size is just right so the interaction of potassium with carbonate pulls the ions through. Lecture 27 (April 8)I. Chemical BondingValence electrons are the outer shell of electrons, with higher values of n, they are the least tightly held electrons. GN Lewis came up with something called Lewis Structures. The periodic table is arranged so that elements with the same number of valence electrons are in the same columns. II. Ionic BondingThis is where a metal and nonmetal exchange electrons. Charges on respective ions have an electrostatic attraction. There is a compound formation which is combining positive and negative charges to obtain a neutral molecule. D= r+ + r- . We want to be able to predict the strength of the ionic bond. Crystalline arrangements maximize the packing of the atoms. Close packing of ions maximizes interactions and measured as a quantity known as lattice energy. III. Lattice EnergyThere are multiple cations and anions that come together to form crystal that reflects energy. We use lattice energy as a