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The periodic table also gives information on molecular bonding. To see this, consider atoms in the left-most column (the so-called alkali metals including: Li, Na, and K). These atoms contain a single electron in the 2 s subshell, which is easily donated to other atoms. In contrast, atoms in the second-to-right column (the halogens: for example, Cl, F, and Br) are relatively stingy in sharing electrons. These atoms would much rather accept an electron, because they are just one electron shy of a filled shell (“of being noble”).
Therefore, if a Na atom is placed in close proximity to a Cl atom, the Na atom freely donates its 2 s electron and the Cl atom eagerly accepts it. In the process, the Na atom (originally a neutral charge) becomes positively charged and the Cl (originally a neutral charge) becomes negatively charged. Charged atoms are called ions. In this case, the ions are and , where the superscript indicates charge of the ion. The electric (Coulomb) attraction between these atoms forms a NaCl (salt) molecule. A chemical bond between two ions is called an ionic bond . There are many kinds of chemical bonds. For example, in an oxygen molecule electrons are equally shared between the atoms. The bonding of oxygen atoms is an example of a covalent bond .
What is Pauli’s exclusion principle? Explain the importance of this principle for the understanding of atomic structure and molecular bonding.
Compare the electron configurations of the elements in the same column of the periodic table.
Elements that belong in the same column in the periodic table of elements have the same fillings of their outer shells, and therefore the same number of valence electrons. For example:
Li:
(one valence electron in the
shell)
Na:
(one valence electron in the
shell)
Both, Li and Na belong to first column.
Compare the electron configurations of the elements that belong in the same row of the periodic table of elements.
(a) How many electrons can be in the shell?
(b) What are its subshells, and how many electrons can be in each?
a. 32; b.
(a) What is the minimum value of l for a subshell that contains 11 electrons?
(b) If this subshell is in the shell, what is the spectroscopic notation for this atom?
Unreasonable result. Which of the following spectroscopic notations are not allowed? (a) (b) (c) (d) (e) . State which rule is violated for each notation that is not allowed.
a. and e. are allowed; the others are not allowed.
b.
not allowed for
c. Cannot have three electrons in
s subshell because
d. Cannot have seven electrons in
p subshell (max of 6)
Write the electron configuration for potassium.
The valence electron of potassium is excited to a 5 d state. (a) What is the magnitude of the electron’s orbital angular momentum? (b) How many states are possible along a chosen direction?
(a) If one subshell of an atom has nine electrons in it, what is the minimum value of l ? (b) What is the spectroscopic notation for this atom, if this subshell is part of the shell?
a. The minimum value of
is
to have nine electrons in it.
b.
Write the electron configuration for magnesium.
The magnitudes of the resultant spins of the electrons of the elements B through Ne when in the ground state are: , , and 0, respectively. Argue that these spins are consistent with Hund’s rule.
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