electron configuration

Examples of electron configuration in the following topics:

• Electron Configurations and Magnetic Properties of Ions

  • The electron configuration of a given element can be predicted based on its location in the periodic table.
  • This is because the elements are listed in part by their electron configuration.
  • In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule in atomic or molecular orbitals.
  • For example, the electron configuration of the neon atom (Ne) is 1s2 2s2 2p6.
  • According to the laws of quantum mechanics, a certain energy is associated with each electron configuration.

• The Building-Up (Aufbau) Principle

  • The Aufbau principle determines an atom's electron configuration by adding electrons to atomic orbitals following a defined set of rules.
  • An element's electron configuration can be represented using energy level diagrams, or Aufbau diagrams.
  • A special type of notation is used to write an atom's electron configuration.
  • For example, the electron configuration of lithium is 1s22s1.
  • Using standard notation, the electron configuration of fluorine is 1s22s22p5.

• Periodic Table Position and Electron Configuration

  • The position of elements on the periodic table is directly related to their electron configurations.
  • The electron shell configurations of the first 18 elements in the periodic table.
  • Position in the periodic table based on electron shell configuration.
  • This image breaks out the electron configuration numerically, showing the population of electrons in each subshell, starting each period with a completely filled noble gas.
  • Use the periodic table to identify atom properties such as groups and electron configurations.

• Electron Configuration of Cations and Anions

  • In such a state, the resulting charged atom has the electron configuration of a noble gas.
  • This transfer is driven by the stabilization that comes by obtaining stable (full shell) electronic configurations.
  • Removal of this one electron leaves sodium stable: Its outermost shell now contains eight electrons, giving sodium the electron configuration of neon.
  • Thus, a chlorine atom tends to gain an extra electron and attain a stable 8-electron configuration (the same as that of argon), becoming a negative chloride anion in the process:
  • Predict whether an atom will undergo ionization to provide an anion or cation based on its valence shell electron configuration.

• The Shielding Effect and Effective Nuclear Charge

  • The element sodium has the electron configuration 1s22s22p63s1.
  • The electron configuration for cesium is 1s22s22p63s23p64s23d104p65s24d105p66s1.
  • Start by figuring out the number of nonvalence electrons, which can be determined from the electron configuration.
  • The electron configuration is 1s22s2 2p6.
  • The electron configuration is the same as for neon and the number of nonvalence electrons is 2.

• General Rules for Assigning Electrons to Atomic Orbitals

  • An atom's electrons exist in discrete atomic orbitals, and the atom's electron configuration can be determined using a set of guidelines.
  • An orbital diagram helps to determine the electron configuration of an element.
  • An element's electron configuration is the arrangement of the electrons in the shells.
  • Electron configurations can be used to rationalize chemical properties in both inorganic and organic chemistry.
  • Determine the electron configuration for elements and ions, identifying the relation between electron shells and subshells.

• Hund's Rule

  • For example, take the electron configuration for carbon: 2 electrons will pair up in the 1s orbital, 2 electrons pair up in the 2s orbital, and the remaining 2 electrons will be placed into the 2p orbitals.
  • The electron configuration can be written as 1s22s22p4.
  • Electron configurations can also predict stability.
  • These configurations occur in the noble gases.
  • Apply Hund's rule and justify its use to determine electron configurations for atoms in the ground state

• Resonance

  • Resonance structures depict possible electronic configurations; the actual configuration is a combination of the possible variations.
  • Lewis dot structures can be drawn to visualize the electrons and bonds of a certain molecule.
  • That is, the molecule does not actually go back and forth between these configurations; rather, the true structure is an approximate intermediate between each of the structures.
  • This intermediate has an overall lower energy than each of the possible configurations and is referred to as a resonance hybrid.
  • Again, in reality, the electronic configuration does not change between the three structures; rather, it has one structure in which the extra electrons are distributed evenly.

• Stereogenic Nitrogen

  • As noted earlier, single-bonded nitrogen is pyramidal in shape, with the non-bonding electron pair pointing to the unoccupied corner of a tetrahedral region.
  • Since the nitrogen in these compounds is bonded to three different groups, its configuration is chiral.
  • The non-identical mirror-image configurations are illustrated in the following diagram (the remainder of the molecule is represented by R, and the electron pair is colored yellow).
  • If these configurations were stable, there would be four additional stereoisomers of ephedrine and pseudoephedrine.
  • It rapidly inverts its configuration (equilibrium arrows) by passing through a planar, sp2-hybridized transition state, leading to a mixture of interconverting R and S configurations.

• The Shape of Molecules

  • The following examples make use of this notation, and also illustrate the importance of including non-bonding valence shell electron pairs (colored blue) when viewing such configurations.
  • Bonding configurations are readily predicted by valence-shell electron-pair repulsion theory, commonly referred to as VSEPR in most introductory chemistry texts.
  • In the three examples shown above, the central atom (carbon) does not have any non-bonding valence electrons; consequently the configuration may be estimated from the number of bonding partners alone.
  • Of course, it is the configuration of atoms (not electrons) that defines the the shape of a molecule, and in this sense ammonia is said to be pyramidal (not tetrahedral).
  • The compound boron trifluoride, BF3, does not have non-bonding valence electrons and the configuration of its atoms is trigonal.