An element, as any scientist knows, is a substance that cannot be chemically interconverted or broken down into simpler substances and are primary constituents of matter. Ancient philosophers and observers of the universe identified the elements as earth, water, air and fire. From our modern understanding, natural abundances of iron, gold, silver, lead, tin, mercury, sulfur and carbon are the very first known elements used to build civilization. Other elements are hiding in mixtures and compounds which could not easily be extracted or purified. Early chemist classified them by their properties and characteristics, subsequently discovering many more (and the way to purify and extract, even synthesize them) with nearly all of the naturally-occuring elements having been discovered by 1900.
One man shed light on the structure and relationships of the the elements by ordering them in a table and sorting them. Dmitri Ivanovich Mendeleev (Дми́трий Ива́нович Менделе́ев) (1834-1907) published his formulation in 1869 to correct the properties of elements and to aide int he prediction of the properties undiscovered elements. This work is known now as the Periodic Table of Elements.
Periodicity Of Elements
The essential model or theory to understand an elements chemical properties came from the early birth of quantum mechanics and is known as electron configuration. The element is modeled as an atom with its "number", the atomic number ( Z ) which represents the number of protons, and therefore the number of electrons as well( in ground state ). The periodicity of the elements might be explained by the electron structure of the atom which can in turn be explained by quantum theory.
An electron within the atom can be described by the four quantum numbers:
- n = the principal quantum number( or simply, quantum number ), e.g: 1,2,3
- l = the orbital quantum number( or simply, angular number ), e.g: 0,1,2
- ml = the orbital magnetic quantum number( or simply, magnetic number ), e.g: -2,-1,0,+1,+2
- ms = the spin magnetic quantum number( or simply, spin number ), e.g: ⁺½ or ⁻½.
|Orbital label||l||Max electrons||Spectroscopic Name|
|g||4||18||( simply in alphabet after f )|
The magnetic quantum number describes the number of orbitals and its orientation in the space of a specific orbital. Consequently, its value depends on the orbital angular momentum quantum number l. The possible value of ml is an interval ranging from -l to +l, so it may be zero, a negative integer, or a positive integer. Unlike n, l, and ml, the spin magnetic quantum number does not depend on another quantum number. It defines the direction of the electrons spin, which value may have ⁺½ (represented by ↾ "spin up") or ⁻½(represented by ⇃ "spin down.")
So far we have explanations for the four quantum numbers that model an elemental atom.
There are principles that must be followed when writing electron configuration; these principles are described below:
Pauli Exclusion Principle or Quantum StateThis principle states that:
There are no two electrons in an atom can exist in the same quantum state.Because the state of any electron is specified by the quantum numbers n, l, ml and ms, the principle simply states that no two electron can have the same set of the four quantum numbers.
Aufbauf Principle or Constructing Up Principlestates that:
A maximum of 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.
Klechkowski's Rule or Occupation of Orbitalstates that:
- Orbitals are filled in the order of increasing n+l.
- Where two orbitals have the same value of n+l, they are filled in order of increasing n
Hund's Rule or Pairing Rulestates the following:
Pairing of electrons take place when all the available degenerate orbitals in a given subshell are filled with one electron each.Orbitals may have identical energy levels when they are of the same subshell (l = 1, then ml are -1, 0, 1, which have similar energy). Then when assigning electrons in orbitals, each electron will first fill all the orbitals with similar energy (read: degenerate orbitals) before pairing with another electron.
Noble Gas Notation
Noble Gas Notation takes a slightly different form as seen here:
[closest noble gas element] [quantum number][orbital name][number of electrons]
Here are some samples (Noble Gasses are located in column 18 (IUPAC),) described below:
|Element||Symbol||Atomic Number( Z )||Electron Configuration||Noble Gas Notation|
|Neon||Ne||10||1s² 2s² 2p⁶||[He] 2s² 2p⁶|
|Argon||Ar||18||1s² 2s² 2p⁶ 3s² 3p⁶||[Ne] 3s² 3p⁶|
|Krypton||Kr||36||1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶||[Ar] 3d¹⁰ 4s² 4p⁶|
|Xenon||Xe||54||1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶||[Kr] 4d¹⁰ 5s² 5p⁶|
|and so on|
Writing Electron Configuration
Electron configuration follows this form:
[quantum number][orbital name][number of electrons]
When writing the electron configuration, we must first write the energy level( quantum number ) then the subshell(orbital number) and the superscript, which is the number of electrons in that specific subshell. Using these rules, we can now start writing the electron configuration for all the elements in the periodic table.
Consider the following element, Oxygen(O) with Z = 8:
|Orbital Diagram:||⇅ ⇅ ⇅↾↾
|Orbital Model:||2 2 2 1 1|
|Electron Configuration:||1s² 2s² 2p⁴|
|Noble Gas Notation:||[He] 2s² 2p⁴|
CheckiO Quantum Task
Your task is to determine the atomic number and electron configuration in the noble gas notation as well as its orbital model, which is 0 - if there are no electrons, 1 - if the electron is in a degenerate orbital, and 2 - for electrons in a full orbital, by its symbolic element. The number of elements is limited to 118 (as of September First, 2013). This task will use superscript for the electron notation, as seen below:
Input data: A string, which is not case sensitive, the symbol of the element
Output data: A list containing the atomic number, configuration notation and orbital model.
assert( checkio( 'H' ) == [ "1", u"1s¹", "1" ] ), "First Test - 1s¹" assert( checkio( 'He' ) == [ "2", u"1s²", "2" ] ), "Second Test - 1s²" assert( checkio( 'Al' ) == [ "13", u"[Ne] 3s² 3p¹", "2 2 222 2 100" ] ), "Third Test - 1s² 2s² 2p6 3s² 3p¹" assert( checkio( 'O' ) == ["8", u"[He] 2s² 2p⁴", "2 2 211"] ), "Fourth Test - 1s² 2s² 2p⁴" assert( checkio( 'Li' ) == [ "3", u"[He] 2s¹", "2 1" ] ), "Fifth Test - 1s² 2s¹" print('All done!')