Ground-state configuration Aufbau principle

Using these quantum mechanical rules, we can now explore the underlying basis of the Periodic Table. To define the ground state configuration of an atom, we add electrons beginning with the lowest energy subshell until the correct number of electrons (equal to the elements atomic number) have been added. This procedure is called the aufbau ( building-up ) principle. 

Electron configurations of some atoms, such as chromium, deviate from the predictions of the Aufbau principle, but the ground-state configuration that results is the configuration with the minimum possible energy. 

Aufbau principle In building up the electronic configuration of an atom or a molecule in its ground state, the electrons are placed in the orbitals in order of increasing energy. 

A neutral helium atom has two electrons. To write the ground-state electron configuration of He, we apply the aufbau principle. One unique set of quantum numbers is assigned to each electron, moving from the most stable orbital upward until all electrons have been assigned. The most stable orbital is always ly( = l,/ = 0, JW/ = 0 ). 

Use the aufbau principle to write the condensed ground state electron configurations for nitrogen, phosphorus, and arsenic. 

The ground-state electron configuration of a multielectron atom is arrived at by following a series of rules called the aufbau principle. 

Aufbau principle The procedure used to find the ground-state electron configuration of an atom or ion. 

Aufbau principles, 126, 130 ground-state electron configurations and notations, 126-129 history of development, 123-124 Pauli exclusion principle, 123 periodicity of atomic properties, 131-132... 

These experimental results for neon are consistent with the electron configuration Ne ls 2s 2p predicted by the aufbau principle. Ionization energies measured in this way are used to construct the energy-level diagram for atoms and to show explicitly the value of the ground-state energy. 

We can combine the LCAO method for with an aufbau principle, analogous to that developed for atoms, to describe the electron configuration of more complex molecules. Electrons available from the two atoms are fed into the MOs, starting with the MO of lowest energy. At most, two electrons can occupy each MO. The ground-state H2 molecule, therefore, accommodates two electrons with opposite spins in a a-gu bonding MO (Fig. 6.10). The diatomic molecule is more stable than the isolated atoms by the energy difference — 2AE. 

In describing ground state electron configuration, the guiding idea is that the total energy of the atom is as low as possible. To determine these configurations, we use the Aufbau Principle as a guide ... 

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