Electron Configurations Lesson PDF

. Section 3 : Electron Configurations Section 3 Electron Configurations YANBU_YEIS. Electron Configurations The arrangement of electrons in an atom is known as the atom’s electron...

. Section 3 : Electron Configurations Section 3 Electron Configurations YANBU_YEIS. Electron Configurations The arrangement of electrons in an atom is known as the atom’s electron configuration. The lowest-energy arrangement of the electrons for each element is called the element’s ground-state electron configuration. Section 3 Electron Configurations YANBU_YEIS. Governing Electron Configurations Rules Hund's Rule Orbitals of equal energy are each Pauli Exclusion occupied by one Aufbau Principle Principle electron before any An electron occupies No two electrons in orbital is occupied the lowest-energy the same atom can by a second orbital that can have the same set of electron, and all receive it four quantum electrons in singly numbers occupied orbitals must have the same spin Section 3 Electron Configurations YANBU_YEIS. Orbital Notation: Best use of Hund’s rule An unoccupied orbital is represented by a line, with the orbital’s name written underneath the line. An orbital containing one electron is represented as:  An orbital containing two electrons is represented as:  The lines are labeled with the principal quantum number and sublevel letter. For example, the orbital notation for helium is written as follows: He  1s Section 3 Electron Configurations YANBU_YEIS. Electron-Configuration Notation Electron-configuration notation eliminates the lines and arrows of orbital notation. Instead, the number of electrons in a sublevel is shown by adding a superscript to the sublevel designation. The helium configuration is represented by 1s2. The superscript indicates that there are two electrons in helium’s 1s orbital. This is usually on your periodic table…check now! Sample Problem A The electron configuration of boron is 1s22s22p1. How many electrons are present in an atom of boron? What is the atomic number for boron? Write the orbital notation for boron. Section 3 Electron Configurations YANBU_YEIS  Sample. Problem A Solution The number of electrons in a boron atom is equal to the sum of the superscripts in its electron- configuration notation: 2 + 2 + 1 = 5 electrons. The number of protons equals the number of electrons in a neutral atom. So we know that boron has 5 protons and thus has an atomic number of 5. To write the orbital notation, first draw the lines representing orbitals. 1s 2s 2p Next, add arrows showing the electron locations. The first two electrons occupy n = 1 energy level and fill the 1s orbital.  The next three electrons occupy the n = 2 main energy level. Two of these occupy the lower- energy 2s orbital. The third occupies a higher-energy p orbital.    1s 2s 2p Section 3 Electron Configurations YANBU_YEIS. Oxygen has 8 electrons. The electron configuration can be written as 1s22s22p4 How many electrons are present in an atom of Oxygen? What is the atomic number for Oxygen? Write the orbital notation for Oxgyen. Section 3 Electron Configurations YANBU_YEIS. Elements of the Second Period In the first-period elements, hydrogen and helium, electrons occupy the orbital of the first main energy level. According to the Aufbau principle, after the 1s orbital is filled, the next electron occupies the s sublevel in the second main energy level. The highest-occupied energy level is the electron-containing main energy level with the highest principal quantum number. Inner-shell electrons are electrons that are not in the highest-occupied energy level. https://www.youtube.com/watch?v=UEPs-GA2s40 Section 3 Electron Configurations YANBU_YEIS. Elements of the Third Period After the outer octet is filled in neon, the next electron enters the s sublevel in the n = 3 main energy level. Noble-Gas Notation The Group 18 elements (helium, neon, argon, krypton, xenon, and radon) are called the noble gases. A noble-gas configuration refers to an outer main energy level occupied, in most cases, by eight electrons. This is a short-hand version that is also on the periodic table…check it! https://www.youtube.com/watch?v=3tyrkxruz88 Elements of the Fourth Period The period begins by filling the 4s orbital, the empty orbital of lowest energy. With the 4s sublevel filled, the 4p and 3d sublevels are the next available vacant orbitals. The 3d sublevel is lower in energy than the 4p sublevel. Therefore, the five 3d orbitals are next to be filled. Section 3 Electron Configurations YANBU_YEIS. Elements of the Fifth Period In the 18 elements of the fifth period, sublevels fill in a similar manner as in elements of the fourth period. Successive electrons are added first to the 5s orbital, then to the 4d orbitals, and finally to the 5p orbitals. SAMPLE QUESTION a. Write both the complete electron-configuration notation and the noble-gas notation for iron, Fe. b. How many electron-containing orbitals are in an atom of iron? How many of these orbitals are completely filled? How many unpaired electrons are there in an atom of iron? In which sublevel are the unpaired electrons located? https://youtu.be/HcXj60cSUX4 Section 3 Electron Configurations YANBU_YEIS