Electron Configuration PDF

Lesson 3 Electron Configuration  New Vocabulary electron configuration aufbau principle Pauli exclusion principle Hund’s rule valence electron electron-dot structure  Ground-State Electron Configuration The arrangement of electrons in an atom is called the atom’s electron conf...

Lesson 3 Electron Configuration  New Vocabulary electron configuration aufbau principle Pauli exclusion principle Hund’s rule valence electron electron-dot structure  Ground-State Electron Configuration The arrangement of electrons in an atom is called the atom’s electron configuration.  Ground-State Electron Configuration The Aufbau Principle The aufbau principle states that each electron occupies the lowest energy orbital available.  Ground-State Electron Configuration The Aufbau Principle Therefore, your first step in determining an element’s ground state electron configuration is learning the sequence of atomic orbitals from lowest energy to highest energy.  Ground-State Electron Configuration The Pauli Exclusion Principle Every electron has an associated spin, similar to the way a top spins on its point. Like a top, an electron can spin in only one of the two directions.  Ground-State Electron Configuration The Pauli Exclusion Principle The Pauli exclusion principle states that a maximum of two electrons can occupy a single orbital, but only if the electrons have opposite spins.  Ground-State Electron Configuration Hund’s Rule Hund’s rule states that single electrons with the same spin must occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same orbitals.  Ground-State Electron Configuration The Pauli Exclusion Principle Electrons in orbitals can be represented by arrows in boxes. An arrow pointing up ↑ represents the electron spinning in one direction, and an arrow pointing down ↓ represents the electron spinning in the opposite direction. An empty box [ ] represents an unoccupied orbital, a box containing a single up arrow ↑ represents an orbital with one electron, and a box containing both up and down arrows ↓↑ represents a filled orbital containing a pair of electrons with opposite spins.  Ground-State Electron Configuration The Pauli Exclusion Principle An s sublevel, with one orbital, can hold a maximum of 2 electrons. A p sublevel, with three orbitals, can hold a maximum of 6 electrons. A d sublevel, with five orbitals, can hold a maximum of 10 electrons. An f sublevel, with seven orbitals, can hold a maximum of 14 electrons.  Ground-State Electron Configuration Hund’s Rule all orbitals will be singly occupied before any is doubly occupied Quantum numbers  1. Orbital notation method  2. Electron configura tion notation method  Electron Arrangement Electron configuration notation method The electron configuration notation designates the principal energy level and energy sublevel associated with each of the atom's orbitals and includes a superscript representing the number of electrons in the orbital.  Electron Configuration Electron configuration for Neon Increasing Energy ______ ______ ______ ______ 2p 2s ______ Electron 1s2 2s2 2p6 1s Spin Orbital Diagram Electron Configuration  Electron Configuration Aufbau diagram shows each orbital O (atomic number 8) ____ ____ ____ ____ ____ 2s 2p 1s electron configuration 1s2 2s2 2p4  Copper Exceptions Expect: 1s2 2s2 2p6 3s2 3p6 4s2 3d9 Actual: 1s2 2s2 2p6 3s2 3p6 4s1 3d10  Silver Expect: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d9 Actual: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 4d10  Chromium Expect: 1s2 2s2 2p6 3s2 3p6 4s2 3d4 Actual: 1s2 2s2 2p6 3s2 3p6 4s1 3d5  Molybdenum Expect: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d4 Actual: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 4d5 Exceptions are explained, but not predicted! Atoms are more stable with half full sublevel  Electron Configuration Let’s Practice  P (atomic number 15) 2 2 6 2 3 1s 2s 2p 3s 3p  Ca (atomic number 20) 2 2 6 2 6 2 1s 2s 2p 3s 3p 4s  As (atomic number 33) 2 2 6 2 6 2 10 3 1s 2s 2p 3s 3p 4s 3d 4p N (atomic number 7) 1s2 2s2 2p3 Na (atomic number 11) 1s2 2s2 2p6 3s1  Valence Electrons Valence electrons are located in the atom’s outermost orbitals—generally associated with the atom’s highest principal energy level. They determine an element’s chemical properties. 8 | 21  Another way to learn the building-up order is to correlate each sublevel with a position on the periodic table.  The principal quantum number, n, correlates with the period number.  Groups IA and IIA correspond to the s sublevel; Groups IIIA through VIIIA correspond to the p sublevel; the “B” groups correspond to the d sublevel; and the bottom two rows correspond to the f sublevel. This is shown on the next slide. 8 | 22 Energy level equals period number minus one Energy level equals period number minus two  Noble Gas Notation Shorthand configuration 1. Find the noble gas closest to the element (without going over). – Ex: For gold (79) that noble gas would be Xenon (54) 2. We write [Xe] and start counting from there. – The first orbital after xenon is 6s so that’s where we start. – [Xe]6s24f145d9  Electron Filling in Periodic Table s s 1 p 2 3 d 4 5 6  7  f    Quiz 1. What does the aufbau principle state? A A maximum of two electrons can occupy a single atomic orbital. B Each electron occupies the highest energy orbital available. C Each electron occupies the lowest energy orbital available. CORRECT D Single electrons with the same spin must occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same orbitals.  Quiz 2. Which of the following is the electron configuration of helium? A 1s1 C 1p1 B 1s2 CORRECT D 1s22s22p6  Quiz 3. Which of the following is true? A Valence electrons do not determine chemical properties. B Valence electrons are in an atom’s innermost orbital. C Valence electrons are generally associated with the atom’s highest principal energy level. CORRECT D Valence electrons are not involved in forming chemical bonds.  Quiz 4. The electron configuration of ground state carbon is 1s22s22p2. How many electrons are in the third p orbital? A 1 C 2 B 4 D 0 CORRECT