Orbital Diagrams, Electron Configuration Notation, Electron-Dot Structures Chapter 5

Lecture Objectives Give the electron configuration for elements when given the Atomic number (in both spectroscopic notation and pictorially). Give the electron configuration for elements when given the Atomic number (in both spectroscopic notation and pictorially). List for any element the last energy level occupied by electrons and the number of electrons occupying the energy level. List for any element the last energy level occupied by electrons and the number of electrons occupying the energy level. Draw a dot diagram of an element to represent the valence electrons. Draw a dot diagram of an element to represent the valence electrons.

N 1s 2s 2p 3s 1s 2s 2p 3s Aufbau Diagrams Uses individual orbitals Uses individual orbitals Gives subshell arrangement Gives subshell arrangement Each orbital takes one electron before any other orbital in the same subshell can receive a second electron Each orbital takes one electron before any other orbital in the same subshell can receive a second electron Also called an orbital diagram Also called an orbital diagram e.g. Orbital Diagram for A Nitrogen Atom e.g. Orbital Diagram for A Nitrogen Atom  

Orbital Diagram for A Magnesium Atom Mg 1s 2s 2p 3s 1s 2s 2p 3s 

Practice Diagram: Write the orbital diagram for the electrons in an oxygen atom.

Diagram Solution: Write the orbital diagram for the electrons in an oxygen atom. 1s 2s 2p 3s 1s 2s 2p 3s   

Practice Diagram: Write the orbital diagram for the electrons in an iron atom.

Diagram Solution: Write the orbital diagram for the electrons in an iron atom. 1s 2s 2p 3s 3p 3d   

Electron Configuration Spectroscopic notation specifies the shorthand for the electrons in an element. Spectroscopic notation specifies the shorthand for the electrons in an element. Quantum number n is the coefficient for each l value, and the number of electrons in each orbital is indicated by superscript values. Quantum number n is the coefficient for each l value, and the number of electrons in each orbital is indicated by superscript values. –e.g. The electron configuration for nitrogen is 1s 2 2s 2 2p 3 –e.g. The electron configuration for magnesium is 1s 2 2s 2 2p 6 3s 2

Practice in Electron Configuration What is the Electron Configuration for oxygen? What is the Electron Configuration for oxygen? 1s 2 2s 2 2p 4 1s 2 2s 2 2p 4 Draw oxygen’s electron configuration as an orbital diagram. Draw oxygen’s electron configuration as an orbital diagram. What is the Electron Configuration for iron? What is the Electron Configuration for iron? 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 Draw iron’s electron configuration as an orbital diagram. Draw iron’s electron configuration as an orbital diagram.

Valence Electrons The valence electrons are the electrons in the outermost orbitals of an atom. The valence electrons are the electrons in the outermost orbitals of an atom. It is only the valence electrons that determine the chemical properties of an element. It is only the valence electrons that determine the chemical properties of an element. The number of valence electrons can easily be determined for Groups 1, 2, and The number of valence electrons can easily be determined for Groups 1, 2, and –These groups are also called 1A, 2A, and 3A-8A, which just happen to represent the total number of valence electrons for the elements in each of these columns.

Valence Electrons The number of valence electrons is less obvious for Group 3-12 elements. The number of valence electrons is less obvious for Group 3-12 elements. –Look at the electron configuration and determine how many electrons are in the last level. This works for all elements through vanadium (atomic number 23). –Beyond this, using this method will give the incorrect configurations for chromium and copper. We’ll learn why in Chapter 6.

Electron Dot Diagram G.N. Lewis created the electron dot diagram in 1902 as shorthand for representing the all- chemically important valence electrons. G.N. Lewis created the electron dot diagram in 1902 as shorthand for representing the all- chemically important valence electrons. The element’s symbol represents the atomic nucleus and inner-level electrons and is surrounded by dots representing the valence electrons. The element’s symbol represents the atomic nucleus and inner-level electrons and is surrounded by dots representing the valence electrons. The dots are placed one at a time around the four sides of the symbol, and then paired up until all 8 (the maximum number of valence electrons) are used. The dots are placed one at a time around the four sides of the symbol, and then paired up until all 8 (the maximum number of valence electrons) are used. –e.g. Li ·

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