# 6.4 Electronic structure of atoms (electron configurations)  (Page 4/15)

 Page 4 / 15

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the 3 s orbital, giving a 1 s 2 2 s 2 2 p 6 3 s 1 configuration. The electrons occupying the outermost shell orbital(s) (highest value of n ) are called valence electrons    , and those occupying the inner shell orbitals are called core electrons ( [link] ). Since the core electron shells correspond to noble gas electron configurations, we can abbreviate electron configurations by writing the noble gas that matches the core electron configuration, along with the valence electrons in a condensed format. For our sodium example, the symbol [Ne] represents core electrons, (1 s 2 2 s 2 2 p 6 ) and our abbreviated or condensed configuration is [Ne]3 s 1 .

Similarly, the abbreviated configuration of lithium can be represented as [He]2 s 1 , where [He] represents the configuration of the helium atom, which is identical to that of the filled inner shell of lithium. Writing the configurations in this way emphasizes the similarity of the configurations of lithium and sodium. Both atoms, which are in the alkali metal family, have only one electron in a valence s subshell outside a filled set of inner shells.

$\begin{array}{}\\ \text{Li:}\phantom{\rule{0.2em}{0ex}}\left[\text{He}\right]2{s}^{1}\\ \text{Na:}\phantom{\rule{0.2em}{0ex}}\left[\text{Ne}\right]3{s}^{1}\end{array}$

The alkaline earth metal magnesium (atomic number 12), with its 12 electrons in a [Ne]3 s 2 configuration, is analogous to its family member beryllium, [He]2 s 2 . Both atoms have a filled s subshell outside their filled inner shells. Aluminum (atomic number 13), with 13 electrons and the electron configuration [Ne]3 s 2 3 p 1 , is analogous to its family member boron, [He]2 s 2 2 p 1 .

The electron configurations of silicon (14 electrons), phosphorus (15 electrons), sulfur (16 electrons), chlorine (17 electrons), and argon (18 electrons) are analogous in the electron configurations of their outer shells to their corresponding family members carbon, nitrogen, oxygen, fluorine, and neon, respectively, except that the principal quantum number of the outer shell of the heavier elements has increased by one to n = 3. [link] shows the lowest energy, or ground-state, electron configuration for these elements as well as that for atoms of each of the known elements.

When we come to the next element in the periodic table, the alkali metal potassium (atomic number 19), we might expect that we would begin to add electrons to the 3 d subshell. However, all available chemical and physical evidence indicates that potassium is like lithium and sodium, and that the next electron is not added to the 3 d level but is, instead, added to the 4 s level ( [link] ). As discussed previously, the 3 d orbital with no radial nodes is higher in energy because it is less penetrating and more shielded from the nucleus than the 4 s , which has three radial nodes. Thus, potassium has an electron configuration of [Ar]4 s 1 . Hence, potassium corresponds to Li and Na in its valence shell configuration. The next electron is added to complete the 4 s subshell and calcium has an electron configuration of [Ar]4 s 2 . This gives calcium an outer-shell electron configuration corresponding to that of beryllium and magnesium.

what is a solution
A liquid mixture in which the minor component (the solute) is uniformly distributed within the major component (the solvent).
Gabby
what is an acid and base
Joy
acids are substances that ionize (break off) in an aqueous solution to produce hydrogen (H+) ions. pH level less than 7  bases produce hydroxide (OH-) ions in solution. pH level greater than 7
Gabby
An acid is a substances when dissolve in water to produce hydrogen ion as the only positive ion or proton. while base is a substances when dissolve in water to produce hydroxide ion .
Lawal
acid is a substance that produce hydrogen ion as only positive ion when dissolve in water
Ayomide
what is flame
my new mix tape
Jake
What is Stoichiometry?
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favour
the relationship between the relative quantities of substances taking part in a reaction or forming a compound, typically a ratio of whole integers.
Gabby
A radioactive subtance has a half life of 20hrs what fraction of the original radioactive nuclear will remain in 80hrs
1/16th
Ian
general properties of transition metal
form stable complexes Have high melting and boiling points Contain large charge/radius ratio Form compounds which are often paramagnetic Are hard and possess high densities Form compounds with profound catalytic activity Show variable oxidation states form coloured ions and compounds.
Gabby
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Same here
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Professor
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Precious
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Professor
what is dative bond?
A coordinate covalent bond, also known as a dative bond or coordinate bond is a kind of 2-center, 2-electron covalent bond in which the two electrons derive from the same atom.
dharshika
how can i write iupac nunber
Emmanuel
In chemical nomenclature, the IUPAC nomenclature of organic chemistry is a method of organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry. It is published in the Nomenclature of Organic Chemistry
Nike
How can I know the logic for writing the configuration of an element?
Brianna
s and p diagram
Papa
I dont understand that
Brianna
what is elemental composition of earth
what if we try copper and the hydrogen what happened
law of definite proportion
Law of Definite Proportion states that all pure samples of the same chemical compound contains the same elements in proportion by mass
Eunice
what is chemistry
It is that branch of Science which deals with the study of composition, structure and properties of matter .... Ok
ShAmy
The branch of natural science that deals with the constitution of substances and the changes that they undergo as a consequence of alterations in the constitution of their molecules
Young
what is the constitution of substance
ShAmy
chemistry is the study of matter and the changes it undergoes.
Bernard
picture of periodic table
what is matter
matter is any thing that has weight or mass and can occupy spaces
Bernard
What are the classes of colloid
percentage composition