Electron Configurations and Sizes
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Section 8.4 Ions: Electron Configurations and Sizes Electron Configurations in Stable Compounds • When two nonmetals react to form a covalent bond, they share electrons in a way that completes the valence electron configurations of both atoms. • When a nonmetal and a representative-group metal react to form a binary ionic compound, the ions form so that the valence electron configuration of the nonmetal achieves the electron configuration of the next noble gas atom. The valence orbitals of the metal are emptied. Return to TOC 1 Section 8.4 Ions Ions: Electron Configurations and Sizes An ion is an atom with a charge Cation – positively charged atom Anion – negatively charged atom The question becomes….why do atoms form ions? 2 Return to TOC Section 8.4 Ions Ions: Electron Configurations and Sizes Atoms will gain or lose e- in an attempt to form the same electron configuration as the closest noble gas. ***Move the LEAST number of e- possible. 3 Return to TOC Section 8.4 Ions Ions: Electron Configurations and Sizes • Atoms in groups 1 and 2 will lose the outer valence e- first. These are the “s” e• Atoms in groups 13-15, below the “stairs” will lose their outer “p” e- first, then their outer “s” e• Exceptions: B, Al tend to lose both the “p” and “s” e- at the same time 4 Return to TOC Section 8.4 Ions: Electron Configurations and Sizes Transition Metals – lose their valence “s” e- first, then they may lose another e- from the “d” sublevel. Exceptions: Ag, Zn, Cd – they do NOT lose e- from the “d” sublevel Why? After they lose their “s” electrons, it takes too much energy to take from the full “d” sublevel 5 Return to TOC Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes Rules for Filling Orbitals – Any orbital may contain 0, 1, or, at most, 2 electrons. – In filling the p, d, and f subsets, each orbital gets a single electron with the same spin as the others before any pairing takes place. – This is because more energy would be required to fill them in any other way. Return to TOC 6 Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes Elements with atomic numbers 14 have only s electrons Elements with atomic numbers 510 also have electrons in p orbitals Elements 2130 have d electrons Elements 5871 have electrons in f orbitals along with all their other electrons. Return to TOC 7 Figure 3.18, pg. 78 Investigating Chemistry, 2nd Edition Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes Beryllium has an atomic number of 4, with two 1s electrons and with two electrons in the 2s orbital. Adding the superscripts gives the total number of electrons. Return to TOC 8 9 Note the exceptions in red. Copper, Cu, also has an unexpected configuration. 10 Section 8.4 Ions: Electron Configurations and Sizes ELECTRON CONFIGURATIONS • It was once suspected that the deposed Emperor Napoleon was poisoned with arsenic. What is the electron configuration of arsenic, As, element number 33? • Following the periodic table from H, to He, to Li, Be, B, C, N, O, F, etc., – We get 1s2, 2s2, 2p6, 3s2, 3p6… – So far we have 2 + 2 + 6 + 2 + 6 = 18 e’s. Return to TOC 11 Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes • 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p3 • Let’s check our math. • 18 + 2 + 10 + 3 = 33, the right number of electrons in a neutral arsenic atom, As. • Since we followed the periodic table, we did not have to memorize the fact that the 4s orbital is filled before the 3d orbitals. • The set of three 4p orbitals is only half-filled. Return to TOC 12 Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes • Because the elements N and P are directly above arsenic, As, in the periodic table, they also have halffilled p subshells. • As a result, these three elements have many chemical similarities. • Now we can begin to see why Mendeleev was able to predict the properties of elements and compounds that had not yet been discovered in 1869. Return to TOC 13 Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes Electron Orbital Configurations The configuration may be written by using boxes to represent each orbital All orbitals MUST be in increasing energy and MUST contain a label 1s 2s 2p Return to TOC 14 Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes Electron Orbital Configurations 1s 2s 2p Arrows are used to represent each electron Before we begin….. Return to TOC 15 Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes Three Rules Aufbau’s Principle – lower energy orbitals fill before proceeding to higher energy orbitals Hund’s Rule – When there are multiple orbitals available in a sublevel, one electron is placed in each orbital before doubling up the electrons Pauli’s Exclusion Principle – Within each orbital, e- must spin in opposite directions; each orbital in a sublevel must spin in the same direction. Return to TOC 16 Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes Aufbau’s Principle To get the orbitals in increasing energy, just follow the periodic table like you would read a book. 1s2s2p3s3p4s3d4p5s4d5p6s4f5d6p Return to TOC 17 Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes Hund’s Rule Never double up electrons in an orbital until each orbital in that sublevel has one electron. Once each orbital in a sublevel has one electron, then begin to double up the electrons. Return to TOC 18 Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes Pauli’s Exclusions Principle Electrons will take the lowest energy configuration possible. This means: 1. All unpaired e- must spin in the same direction. 2. All paired e- must spin in opposite directions Return to TOC 19 Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes Electron Orbital Configurations 1s 2s 2p Hydrogen Atomic # =1 , 1e- Return to TOC 20 Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes Electron Orbital Configurations 1s 2s 2p Helium – Atomic Number = 2 Return to TOC 21 Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes Electron Orbital Configurations 1s 2s 2p Boron – Atomic Number = 5 Return to TOC 22 Section 8.4 ELECTRON Ions:CONFIGURATIONS Electron Configurations and Sizes Stable Compounds • Atoms in stable compounds usually have a noble gas electron configuration. Return to TOC 23 Noble Gas Configuration What is a noble gas? Noble gases are located in group 8A, 18 on the periodic table. Noble gases are extremely unreactive, because their outer energy level is filled 24 Noble Gas Configurations Noble gases include: He Ne Ar Kr Xe Rn 25 Noble Gas Configurations Aufbau tells us that all lower sublevels MUST be filled before filling sublevels of higher energy. This results in us writing the same information repeatedly when making short hand configurations: Mn 1s22s22p63s23p64s23d5 Cl 1s22s22p63s23p5 Ca 1s22s22p63s23p64s2 26 Noble Gas Configurations Rules: Choose the largest noble gas that has an atomic number LESS than the element you are working with. For Mn, the largest noble gas is Ar 27 Noble Gas Configurations Because we know that lower sublevels are already filled, we can substitute part of the configuration with a noble gas: Mn 1s22s22p63s23p64s23d5 Ar 1s22s22p63s23p6 Therefore we write: [Ar] 4s23d5 28 Noble Gas Configurations Now try it for Cl Cl 1s22s22p63s23p5 The largest noble gas is Ne 1s22s22p6 [Ne] 3s23p5 Valence electrons – these ARE used in bonding Core electrons – these are NOT used when bonding 29 Noble Gas Configurations Write the noble gas configurations for: As I Pb Au W 30 Noble Gas Configurations Write the noble gas configurations for: As [Ar] 4s23d104p3 I [Kr] 5s24d105p5 Pb [Xe] 6s24f145d106p2 Au [Xe] 6s24f145d9 W [Xe] 6s24f145d4 31 Exceptional Configurations ….and ions 32 Exceptions to Aufbau There is a general stability associated with electron configurations Filled sublevels are MOST stable ½ Filled sublevels are stable All other configurations for sublevels are LEAST stable 33 Exceptions to Aufbau Sometimes by moving electrons between sublevels that are close in energy, atoms can achieve a more stable configuration. Examples include: s 2d 4 Because d5 is ½ filled and more stable, the atom takes on the configuration of s 1d 5 34 Exceptions to Aufbau Cr [Ar] 4s13d5 Mo [Kr] 5s14d5 W [Xe] 6s14f145d5 35 Exceptions to Aufbau Another exception occurs with the configuration: s2d9 Again, by moving 1e- from the “s” sublevel to the “d” sublevel, the “d” sublevel becomes filled. s1d10 36 Exceptions to Aufbau Cu [Ar]4s13d10 Ag [Kr]5s14d10 Au [Xe]6s14f145d10 37 WARNING Exceptional configurations only happen between “s” and “d” sublevels….NEVER between “s” and “p” sublevels. 38
