Helium atom electron configuration

Lets consider the covalent bond in the hydrogen molecule. A hydrogen molecule forms from two hydrogen atoms, each with one electron in a Is orbital. The two hydrogen atoms are attracted to the same pair of electrons in the covalent bond. The bond is represented either as a pair of dots or as a solid hne. Each hydrogen atom acquires a helium-like electron configuration. 

Example The electron configuration for Be is Is lsfi but we write [He]2s where [He] is equivalent to all the electron orbitals in the helium atom. The Letters, s, p, d, and f designate the shape of the orbitals and the superscript gives the number of electrons in that orbital. 

A hydrogen atom (Z = 1) has one electron a helium atom (Z = 2) has two The single electron of hydrogen occupies a Is orbital as do the two electrons of helium We write their electron configurations as... 

The covalent, or shared electron pair, model of chemical bonding was first suggested by G N Lewis of the University of California m 1916 Lewis proposed that a sharing of two electrons by two hydrogen atoms permits each one to have a stable closed shell electron configuration analogous to helium... 

The analogy is even closer when the situation in oxygen is compared with that in excited configurations of the helium atom summarized in Equations (7.28) and (7.29). According to the Pauli principle for electrons the total wave function must be antisymmetric to electron exchange. 

From Figure 6.8 it is possible to predict the electron configurations of atoms of elements with atomic numbers 1 through 36. Because an s sublevel can hold only two electrons, the Is is filled at helium (Is2). With lithium (Z = 3), the third electron has to enter a new sublevel This is the 2s, the lowest sublevel of the second principal energy level. Lithium has one electron in this sublevel (ls s1)- With beryllium (Z = 4), the 2s sublevel is filled (ls22s2). The next six elements fill the 2p sublevel. Their electron configurations are... 

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 ). 

The charge on the nucleus and the number of electrons in the valence shell determine the chemical properties of the atom. The electron configurations of the noble gases (except for that of helium) correspond to a valence shell containing eight electrons—a very stable configuration called an... 

It must be emphasized that the octet rule does not describe the electron configuration of all compounds. The very existence of any compounds of the noble gases is evidence that the octet rule does not apply in all cases. Other examples of compounds that do not obey the octet rule are BF,. PF5, and SF6. But the octet rule does summarize, systematize, and explain the bonding in so many compounds that it is well worth learning and understanding. Compounds in which atoms attain the configuration of helium (the duet) are considered to obey the octet rule, despite the fact that they achieve only the duet characteristic of the complete first shell of electrons. 

For hydrogen, the notation Is1 is used, where the superscript denotes a single electron in the Is state. Because an electron can have a spin quantum number of +1/2 or -1/2, two electrons having opposite spins can occupy the Is state. The helium atom, having two electrons, has the configuration Is2 with the electrons having spins of +1/2 and —1/2. 

Fig. 13.4 Logarithm of error(Eh) in the configuration interaction energy for the ground state of the helium atom as a function of maximum orbital quantum number, L, of the one-electron basis functions. The data were obtained in an...

Refer to the sets of quantum numbers for hydrogen and helium that you saw earlier. Then use the quantum numbers for lithium to infer why a lithium atom has the ground state electron configuration that it does. 

As mentioned previously, in 1916, Lewis noted that noble gases were particularly stable and did not form compounds. Lewis used these facts to formulate the octet rule. The noble gases have their outer electron shell filled with eight electrons. (Helium is an exception with only two electrons in its outer shell.) The octet rule says that the most stable electron configuration of an atom occurs when that atom acquires the valence electron configuration of a noble gas. That is, when an atom can acquire eight (octet) electrons in its valence shell (or two for hydrogen to become like helium). 

Atoms form bonds in order to obtain a stable electronic configuration, i.e. the electronic configuration of the nearest noble gas. All noble gases are inert, because their atoms have a stable electronic configuration in which they have eight electrons in the outer shell except helium (two electrons). Therefore, they cannot donate or gain electrons. 

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