Electron configuration is the arrangement of electrons of an atom, a molecule, or other physical structure. Knowledge of electron configuration useful in understanding the structure of the periodic table and the chemical bond that hold the atoms together. Electrons are able to move from one orbital to another by emission or absorption of a quantum energy, in the form of a photon. The electron configuration is based on the Aufbau principle, Hund principle, and Pauli principle. One shell can hold 2n2 electrons. But, the last shell can not hold more than 8 electrons and if the electrons is more than 8, the 8 electrons move to the new shell before the last shell and the rest electron(s) is(are) in the last shell and that electron would called as the valence electron. Valence electron(s) is(are) important in determining how the atom reacts chemically with other atoms. Group of an element in the periodic table is depends on the number of valence electron that the element has. If the valence electron is 1, then that element belongs to group 1. The period of an element is depends on the number of the shell that each element has. If the number of shells are 2, means that element has period number of two. The elements that are in the same group have some similarity in their chacteristics of the physical and chemical properties.

Niels Bohr was the first to propose that the periodicity in the properties of elements can be explained by the electronic structure of the atom. Bohr’s original configurationns would seem strange to a present day chemist, sulfur was given as 2.4.4.6 instead of 1s2 2s2 2p6 3s2 3p4 (2.8.6). The following year E.C. Stoner incorporated Sommerfeld’s third quantum number into the description of the electron shells, and correctly predicated the shell structure of the sulfur to be 2.8.6. However, neither Bohr’s and Stoner’s system could correctly describe the changes in atonomic spectra in a magnetic field (the Zeeman effect). Bohr was aware of this shortcoming and had written to his friend, Wolfgang Pauli to ask for his help in saving quantum theory. Pauli realized that the Zeeman effect must due only by the outermost electons of the atom, and was able to reproduce Stoner’s shell structure, but with the correct structure of sub shells, by his inclusion of a fourth quantum number and his exclusion principle:
It should be forbidden for more than one electron with the same value of the main quantum number n to have the same value for the other three quantum numbers k [l], j [ml] and m [ms].

The Aufbau Principle was an important part of Bohr’s original concept of electron configuration. It may be stated as:
A maximum two electrons are put into orbitals in the order of increasing orbital energy: the lowest energy orbitals are filled before electrons are placed in higher energy orbitals.

The Allende meteorite fell at 1:05 AM (local time) on February 8, 1969. It created a huge fireball then shattered and rained fragments over the area of the strewn field in Chihuahua, Mexico State.It scattered thousands of fragments over an area of 48 km × 7 km. The Allende Meteorite is classified as meteorite that has type of chondrite meteorite, class of carbonaceous chondrite, and group of CV3. Like many meteorites, The Allende entered the atmosphere and friction began to heat it up. The main mass of the meteorite exploded and the fragments fell over the area that shown in the picture as the "Allende strewn field”. It was named with a village that near the place where that meteorite fell, Pueblito de Allende.

untuk manusia yang telah lama kuijinkan tinggal di dalamku