Electron configuration and valency

When the orbitals in the outermost shell are filled, we have a lone pair 

The outermost shell of the atom (in the preceding example of chlorine, the outermost shell is the 3p-orbital, which contains five electrons) is called the valence shell and the electrons contained within this shell are called the valence electrons. These electrons have the highest amount of energy in the atom and are therefore the most reactive. For this reason, these electrons will participate in bonding and chemical reactions. All other electrons within the atom generally do not participate in such reactions. 

The reason that we find two electrons in separate p-orbitals (2py and 2pJ is that electrons do not want to share the space, unless they really have to. Electrons, in this manner, are like humans on a bus No one wants to sit next to someone unless there are no other spaces available. The space that is left in the orbitals means that oxygen has a valency of two, which means that oxygen can bond with two other elements (with a valency of one) or form a double bond with one other element. 

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In a previous section, we looked at the electron configuration and valency concept that electrons present within an electron cloud are in continual random motion. Because the electrons may collect at one end of a molecule, we can find an instantaneous or fleeting dipole moment this results in a molecule having a temporary positive or negative charge at certain times. It is these charges that will be attracted to each other and are termed Van der Waals forces. 

UV/Vis Spectra for Molecules and Ions When a molecule or ion absorbs ultraviolet or visible radiation it undergoes a change in its valence electron configuration. The valence electrons in organic molecules, and inorganic anions such as oc-... 

Give the valence-shell electron configurations and bond orders for CO and CO+. Use that information to predict which species has the greater bond enthalpy. 

Write the shorthand electron configuration and draw the ground-state orbital energy level diagram for the valence electrons in a sulfur atom. 

C08-0050. Write the complete electron configuration, and list a correct set of values of the quantum numbers for each of the valence electrons in the ground-state configurations of (a) Be, (b) O, (c) Ne, and... 

Periodic table A chart that arranges the elements by atomic number in a way that the vertical columns produce groups of elements with similar valence electron configurations and chemical properties. 

For each of the elements below, use the aufbau principle to write the full and condensed electron configurations and draw partial orbital diagrams for the valence electrons of their atoms. You may consult the periodic table in Appendix C, or any other periodic table that omits electron configurations. 

Symbol Ba atomic number 56 atomic weight 137.327 a Group llA (Group 2) alkaline earth element electronic configuration [Xejs valence state +2 ionic radius of Ba2+ in crystal (corresponding to coordination number 8) 1.42 A first ionization potential lO.OOeV stable isotopes and their percent abundances Ba-138 (71.70), Ba-137 (11.23), Ba-136 (7.85), Ba-135 (6.59), Ba-134 (2.42) minor isotopes Ba-130 (0.106) and Ba-132 (0.101) also twenty-two radioisotopes are known. 

Symbol B atomic number 5 atomic weight 10.811 a Group III A (Group 13) metalloid element atomic volume 4.70 cc/g-atom electron affinity 0.277 eV electronic configuration Is22s22pi valence state +3 naturally occurring stable isotopes are B-10 and B-11 and their abundance 19.57% and 80.43%, respectively. 

Symbol He atomic number 2 atomic weight 4.0026 a Group 0 (Group 18) inert gas element second hghtest element electron configuration Is valence 0 no chemical compound known atomic radius 0.33A isotope He-3 is found in trace concentration in He-4 natural abundance of He-3 1.37 ppm short-hved radioisotopes He-5, He-6, and He-8 are known. 

Symbol H atomic number 1 atomic weight 1.0079 the lightest of all the chemical elements the first element in the Periodic Table Group lA (group 1) nonmetallic gaseous element occurs as H2, a diatomic molecule electron configuration Ish valences -i-l and-1 three isotopes H-1 or protium (99.9844%), H-2 or deuterium (0.0156%), H-3 or tritium (radioactive, ty, =12.4 yr., in traces... 

The alkaline earth elements in group 2A—Be, Mg, Ca, Sr, Ba, and Ra—are similar to the alkali metals in many respects. They differ, however, in that they have ns2 valence-shell electron configurations and can therefore lose two electrons in redox reactions. Alkaline earth metals are thus powerful reducing agents and form ions with a +2 charge. 

In neutral molecules and complex anions, the metal atom usually has a positive oxidation state. It therefore has a partial positive charge and a higher Zeff than that of the neutral atom. As a result, the 3d orbitals are again lower in energy than the 4s orbital, and so all the metal s valence electrons occupy the d orbitals. The metal atom in both VCI4 and MnC>42-, for example, has the valence configuration 3d1. Electron configurations and other properties for atoms and common ions of first-series transition elements are summarized in Table 20.1. 

The term was first used by Van Vleck who explained it thus, referring to carbon in CH4 ...the spins of the four electrons belonging to sp3 were assumed paired with those of the four atoms attached by the carbon. Such a condition of the carbon atom we may conveniently call its valence state. He then showed a calculation which led to the conclusion that The valence state of C has about 7 or 8 more volts of intra-atomic energy than the normal state. This is the energy required to make the C atom acquire a chemically active condition... [1]. Mulliken defines it saying [it is] a certain hypothetical state of interaction of the electrons of an atomic electron configuration and A valence state is an atom state chosen so as to have as nearly as possible the same condition of interaction of the atom s electrons with one another as when the atom is part of a molecule. [2]. 

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