Chem 101 1st Edition Lecture 5 Outline of Last Lecture I. Atoms, electrons, neutrons, protons, energy levels and Dalton’s Atomic Theory Outline of Current Lecture II. Electron ConfigurationsIII. The Periodic Table and ConfigurationsIV. Noble Gas ConfigurationsCurrent LectureI. Electron Configurations: describes the arrangement of electrons in space around the nucleus. The electron configuration of an atom shows the number of electrons in each sublevel in each energy level of the ground-state atom. a. To determine the electron configuration of a particular atom, start at the nucleus and add electrons one by one until the number of electrons equals the number of protons in the nucleus. Each added electron is assigned to the lowest-energy sublevel available. We talked about sublevels during the last lecture. b. The first sublevel filled will be the 1s sublevel, then the 2s sublevel, the 2p sublevel, the 3s, 3p, 4s, 3d, and so on. Sublevels must be maximized before filling another level or orbital. (There are exceptions to this rule but you are not responsible for those sequences. These exceptions can be found on page 82 of thetext, in red ink.)c. Here is a more convenient way to remember the order: The principal energy levelsare listed in columns, starting at the left with the 1s level. To use this figure, read along the diagonal lines in the direction of the arrow. The order is summarized under the diagramThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.FIGURE 5.1 The arrow shows a second way of remembering the order in which sublevels fill. d. Let us look at a hydrogen atom. As you know it has an atomic number of 1 and therefore has 1 proton and 1 electron. The single electron is assigned to the 1s sublevel, the lowest-energy sublevel in the lowest-energy level. As stated in the last lecture this would be called a ground state electron.i. Therefore, the electron configuration of hydrogen is written:ii. The element lithium Li (atomic number 3) has three electrons. Therefore, the electron configuration of lithium is: 1s22s1iii. An electron configuration for an atom with every orbital completely filled would be written: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d107p68s2 iv. You must be able to write out the sequence of electrons for all the elements you are responsible for memorizing. II. The Periodic Table & Electron Configurations a. Below is a lay out if the periodic table visualizing the orbital sequence.b. We can actually use the periodic table to make the task of writing out these configurations easier. Notice there is only 2 elements in the first period (the first row of the periodic table); their electrons are in what we call the first principal energy level: n =1. The second period (row) contains a total of 8 elements, which all have 2 sublevels; s and p. c. As you may recall s sublevels contain 2 electrons when full while p sublevels contain 6 electrons when full (because p sublevels each contain three orbitals). d. Notice that it takes less energy for an electron to be placed in 4s than 3d, so 4s fills before 3d. e. The middle of the periodic table (d- block) contains a square of 10 columns: these are where the elements in which the d orbitals are being filled. These are the transition metals. i. You can use the periodic table to quickly determine the valence electron configuration of each element. Valence electrons are the outermost electrons in an atom, furthest away from the nucleus (These are the electrons available are responsible for chemical reactions and bonding). ii. When you get your periodic table with the exam label it in the same manner shown above. The numbers at the top (i.e., 1A, 2A, 3A etc.) will tell you how many valence electrons each element in that particular column has.f. Valence shell electrons: these are the electrons of interest to chemists. They are found in the outermost s and p orbital electrons. They are involved in chemical reactions, gaining, losing and sharing electrons. g. Core Electrons: are not involved in chemical reactions (except in rare cases) these are the inner electrons that make up the beginning of the electron configuration. III. Noble Gas Configurationsa. These are shorthand electron configurations using the noble gases.i. Find the symbol for the element you are writing the configuration for on aperiodic table.ii. Then write the symbol [in brackets] for the noble gas that is located at thefar right of the preceding horizontal row on the periodic table.1. If we did Zinc as an example we would find Zn on the periodic table and then look up to the 3rd period and across to the column of noble gases to land on Ar. So we would write Ar in brackets: [Ar]iii. Move back down a row (to the row containing the element you wish to describe) and to the far left. Following the elements in the row from left to right, write the outer-electron configuration associated with each column until you reach the element you are describing.1. For zinc, we need to describe the 19th through the 30th electrons.The atomic numbers 19 and 20 are in the fourth row of the s block, so the 19th and 20th electrons for each zinc atom enter the 4s2 sublevel. The atomic numbers 21 through 30 are in the first row of the d block, so the 21st to the 30th electrons for each zinc atom fill the 3d sublevel (see below). Zinc, with atomic number 30, has the abbreviated configuration:[Ar] 4s23d10 Which is short for: Zn: