Orbital Diagrams & Electron Configurations for Atoms and Ions

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Orbital Diagrams & Electron Configurations for Atoms and Ions Section 3.

Orbital diagrams represent the arrangement of electrons in orbitals.

opposite spin) The aufbau principle: The atom is built up by progressively adding Electrons will fill the lowest available

1 Orbital Diagrams & Electron Configurations for Atoms and Ions Section 3.5 The Periodic Table is like a MAP that describes the arrangement of electrons within their orbitals. Orbital diagrams represent the arrangement of electrons in orbitals. boxes or lines represent each orbital arrows within boxes represent the electrons max two per box opposite direction (represents opposite spin) The aufbau principle: The atom is built up by progressively adding Electrons will fill the lowest available energy levels first, before filling higher levels. e.g., Hydrogen (Z=1) e.g., Helium (Z=2) Within a principal energy level, s < p < d < f Order for orbital filling Example: 3s fills before 3p But the (n+1)s orbitals always fill before the nd orbitals. Example: 5s fills before 4d

2 Practice! Draw an orbital diagram for beryllium (Z=4) Guidelines for drawing orbital diagrams 1. Fill orbitals in order of increasing energy. 2. Orbitals of the same energy level must be filled before moving onto the next energy level. 3. Place electrons singly into orbitals within a sublevel before any pairing occurs. Hund s rule: To achieve the lowest possible energy, electrons will spread out singly before pairing up within an orbital. 2s 2p 2s 2p 7 N nitrogen O oxygen Orbital diagrams for ions anion (negative charge): ADD appropriate number of electrons cation (positive): REMOVE appropriate number of electrons Example: Oxide ion, O 2-2s 2p Practice! Draw orbital diagrams for: a) Sulfur (Z=16) b) Iron (Z=26) Before beginning, ask yourself: a) How many e - in a neutral oxygen atom? b) How many e - do I add/remove? c) What s the new total number of e -? c) Aluminum (Z=13) d) Nitride ion (Z=7) Tip: Use lines instead of boxes to represent the orbitals.

Learning Checkpoint Just as protons are added on with each

the orbitals in order of increasing energy (Aufbau

An orbital diagram is a visual representation of an atom s

divided into blocks : Blocks represent which orbitals are

3 Learning Checkpoint Just as protons are added on with each successive element, electrons can be envisioned as filling an atom s orbitals. Calcium 3s 2 3p 6 4s 2 Helium 2 Neon Electrons will fill the orbitals in order of increasing energy (Aufbau principle). An orbital diagram is a visual representation of an atom s Scandium 3s 2 3p 6 4s 2 3d 1 The periodic table can be divided into blocks : Blocks represent which orbitals are being filled for each element. Pb is located in the 6p block. Its valence electrons will be found in the 6p orbitals. Ti In which orbital will you find the outermost electron of Titanium? Check your periodic table: In which orbital would you find the outermost electron for gold (Z=79)?

Two exceptions to the pattern: Cr and Cu Learning Checkpoint Possible explanation: Filled and half-filled sub-shells have lower energy than unfilled ones more stable An element s location on the

81 Guidelines for writing electron configurations 1. Write out subshells that have electrons in them. 2. Use superscripts to indicate how many electrons are in each subshell. Practice!

4 Two exceptions to the pattern: Cr and Cu Learning Checkpoint Possible explanation: Filled and half-filled sub-shells have lower energy than unfilled ones more stable An element s location on the periodic table reflects the location of its outermost Chromium: [Ar] 4s 3d An electron configuration is a shorthand notation that provides the same information as the orbital diagram. 5 B boron Guidelines for writing electron configurations 1. Write out subshells that have electrons in them. 2. Use superscripts to indicate how many electrons are in each subshell. Practice! Write electron configurations for: a) Sulfur (Z=16) b) Iron (Z=26) c) Aluminum (Z=13) For simplicity, electron configurations can be abbreviated: Gold: 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 9 = [Xe] 6s 2 4f 14 5d 9 Nearest preceding noble gas All the extra electrons d) Gold (Z=79)

Electron configurations can explain periodic

Electron configurations of ions Elements in a group:

properties: chemical, physical Na: 3s 1 Na + : Mg: 3s

All of these ions are ISOELECTRONIC with Neon.

Na +, Mg 2+, and Al 3+ are isoelectronic with neon.

metals can have more than one ionic charge.

more orbitals = more possibilities Lose 2e - Pb 2+ :

6p 2 Lose 4e - Pb 4+ : [Xe] 6s 0 4f 14 5d 10 6p 0 MO

5 Electron configurations can explain periodic properties. Electron configurations of ions Elements in a group: same valence electron configuration common properties: chemical, physical Na: 3s 1 Na + : Mg: 3s 2 Al: 3s 2 3p 1 Why do atoms form ions? All of these ions are ISOELECTRONIC with Neon. They have the same electron configuration as Ne. Na +, Mg 2+, and Al 3+ are isoelectronic with neon. What other ions would have the same electron configuration? F: 2 2s 2 2p 5 F - : O: 2 2s 2 2p 4 Multivalent metals can have more than one ionic charge. Transition Metals d-block elements examples? more orbitals = more possibilities Lose 2e - Pb 2+ : [Xe] 6s 2 4f 14 5d 10 6p 0 Pb: [Xe] 6s 2 4f 14 5d 10 6p 2 Lose 4e - Pb 4+ : [Xe] 6s 0 4f 14 5d 10 6p 0 MO ORBITALS MO PROBLEMS Summary Orbital diagrams use boxes or lines to visually represent the orbitals of atoms. Arrows are used to represent Electron configurations convey the same information, but in a more condensed form.

Electron Arrangement - Part 2

Brad Collins Electron Arrangement - Part 2 Chapter 9 Some images Copyright The McGraw-Hill Companies, Inc. Review Energy Levels Multi-electron 4d 4d 4d 4d 4d n = 4 4s 4p 4p 4p 3d 3d 3d 3d 3d n=3, l = 2