1. States of Matter. The Atom and the Periodic Table
1.7. Beyond Bohr's Atomic Model
Electrons are actually not tiny marbles of negatively charged matter.
- The electron is “smeared” in time and space.
- One cannot determine the electron’s speed and its position at the same time.
- One can only determine where an electron is with some specific probability.
Because of this, we talk about elecron clouds; a "cloud" where there is some probability that the electron is.
Shells and orbitals
All the electrons in a shell have the same average energy. The electrons may reside in different energy levels (orbitals) within the same shell.
- All the electrons in a certain shell have the same average energy.
- Each orbital may contain max 2e–.
The K shell
Contains a single orbital, 1s.
- Since the K shell only contains one orbital (1s), and each orbital maximally contains 2e–, there can be only two electrons in the K shell.
The L shell
- One s orbital, 2s
- Maximally 2e–
- Three p orbitals, 2p
- Maximally 3 × 2e– = 6e–
In total: Maximally 8e– in the L shell.
The p orbitals
The M and N shells
The M shell has three energy levels:
- One s orbital, 3s
- Three p orbitals, 3p
- Five d orbitals, 3d
The N shell has four energy levels:
- One s orbital, 4s
- Three p orbitals, 4p
- Five d orbitals, 4d
- Seven f orbitals, 4f
Note: The 3d and 4f orbitals overlap.
- The energy of the electrons in the 4s orbitals are lower than the energy of the electrons in the 3d orbitals.
- The 4f orbitals are filled before the 3d orbitals.
The Madelung rule (the Aufbau principle)
Let's look at the electron configurations for a few atoms.
Note: The 3s and 3p orbitals in the M shell are completely filled.
In potassium, 19K, the next electron ends up in the 4s orbital of the N shell, because there its energy is lower than in the 3d orbital of the K shell.
- This is why there are never nine electrons in the outermost shell, only eight electrons at most.
The electron configuration for 19K:
Let's also look at the electron configuration for calcium, 20Ca:
In calcium, the N shell's 4s orbital is filled in calcium. The next electron (in scandium, 21Sc) must be placed in one of the M shell's 3d-orbitals:
When the M shell's 3d-orbitals are filled, we can start adding electrons the N shell's 4p orbitals. In gallium, 31Ga, there are 10e– in the M shell's 3d orbitals, and the last electron ends up in the 4p orbital of the N shell. This means there are 3e– in the N shell:
In krypton, 36Kr, the 4p orbitals have been filled up with 6e–, leading to 8e– in the N shell:
The rest of the orbitals are filled in order according to the Madelung rule (the Aufbau principle). The arrows indicate in which order the orbitals are filled:
Writing ground states
Using the Madelung rule, we can determine the electron configuration for e.g. argon 18Ar. Each superscripted number indicates the number of electrons in the orbitals:
- 1s2 2s2 2p6 3s2 3p6
Another example, zinc 30Zn:
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10
Since the first five orbitals are identical to 18Ar, we can also write the electron configuration for zinc 30Zn like this:
- [Ar] 3d10 4s2
- 1. States of Matter. The Atom and the Periodic Table
- 1.1. Matter. States of Matter
- 1.2. Elements and Chemical Compounds. Pure Substances and Mixtures
- 1.3. The Birth of Chemistry
- 1.4. Atomic Theory. The Atomic Model
- 1.5. Atomic Number, Mass Number, and Atomic Mass
- 1.6. Electron Configurations
- 1.7. Beyond Bohr's Atomic Model
- 1.8. Redox Reactions
- 1.9. The Structure of the Periodic Table
- 1.10. The Noble Gases
- 1.11. The Alkali Metals and the Halogens
- 1.12. The Alkaline Earth Metals and the Oxygen Group
- 1.13. A Few of the Elements in Group 13, 14, and 15
- 2. Chemical Calculations
- 2.1. Physical Quantity, Magnitude, and Units
- 2.2. Atomic Mass, Molecular Mass, and Unit Mass
- 2.3. Amount of Substance, Molar Mass, and Mass
- 2.4. Stoichiometry. Conservation of mass
- 2.5. Water of Crystallization
- 2.6. Calculating the Formula of a Chemical Compound
- 2.7. From Empirical to Molecular Formulas
- 2.8. Equivalent Amounts of Substance and Masses
- 2.9. Gases and Pressure
- 2.10. Concentrations
- 2.11. Dilutions
- 2.12. Yield
- 2.13. Limiting Reactants
- 3. Chemical Bonding
- 3.1. How Ionic Compounds are Formed
- 3.2. Precipitations
- 3.3. Names and Formulas of Ionic Compounds
- 3.4. Ionic Bonds
- 3.5. Properties of Ionic Compounds
- 3.6. Metal Bonding
- 3.7. Covalent Bonds
- 3.8. Polar Covalent Bonding
- 3.9. Dipoles. Polar and non-polar Molecules
- 3.10. The VSEPR Theory
- 3.11. Hydrogen Bonding. The Peculiar Water
- 3.12. Equals Solves Equal
- 3.13. Solubility of Gases in Water
- 3.14. Solubility of Salts in Water
- 4. Thermochemistry
- 5. Chemical Equilibrium
- 5.1. Reaction Rates
- 5.2. The Law of Mass Action
- 5.3. Calculations on Chemical Equilibrium
- 5.4. Heterogenous Equilibria. Solubility Product
- 5.5. Is the System at Equilibrium? The Reaction Quotient Q
- 5.6. Changing the Concentrations in a System in Equilibrium.
- 5.7. Diluting or Compressing Systems in Equilibrium, or Changing the Temperature
- 6. Acids and bases
- 7. Oxidation and Reduction
- 8. Electrochemistry
- 9. Organic Chemistry
- 9.1. Alkanes
- 9.2. Chain Isomers. Nomenclature
- 9.3. Haloalkanes
- 9.4. Nucleophilic Substitution
- 9.5. Alkenes
- 9.6. Electrophilic Addition. Markovnikov’s Rule
- 9.7. Elimination
- 9.8. Alkynes
- 9.9. Arenes and Aromatic Compounds
- 9.10. Alcohols
- 9.11. Oxidation of Alcohols
- 9.12. Aldehydes and Ketones
- 9.13. Thiols and Disulfides
- 9.14. Ethers
- 9.15. Amines
- 9.16. Nitro Compounds and Organic Nitrates
- 9.17. Carboxylic Acids
- 9.18. More on Carboxylic Acids
- 9.19. Stereoisomerism
- 9.20. Esters
- 9.21. Lipids
- 9.22. Mono-, Oligo-, and Polysaccharides
- 9.23. Amino Acids
- 9.24. Nucleotides
- 10. Biochemistry
- 10.1. Proteins
- 10.2. Enzymes
- 10.3. Catabolic Processes
- 10.4. Carrier Molecules
- 10.5. Glycolysis
- 10.6. Beta-oxidation
- 10.7. The Citric Acid Cycle
- 10.8. The Metabolism of Amino Acids
- 10.9. The Electron Transport Chain
- 10.10. Anabolic Processes
- 10.11. Gluconeogenesis and Fatty Acid Synthesis
- 10.12. DNA: Structure and Function
- 11. Analytical chemistry