Periodic table

Group	1	2		3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
Period 1	1 H																		2 He
2	3 Li	4 Be												5 B	6 C	7 N	8 O	9 F	10 Ne
3	11 Na	12 Mg												13 Al	14 Si	15 P	16 S	17 Cl	18 Ar
4	19 K	20 Ca		21 Sc	22 Ti	23 V	24 Cr	25 Mn	26 Fe	27 Co	28 Ni	29 Cu	30 Zn	31 Ga	32 Ge	33 As	34 Se	35 Br	36 Kr
5	37 Rb	38 Sr		39 Y	40 Zr	41 Nb	42 Mo	43 Tc	44 Ru	45 Rh	46 Pd	47 Ag	48 Cd	49 In	50 Sn	51 Sb	52 Te	53 I	54 Xe
6	55 Cs	56 Ba	*	57 La	72 Hf	73 Ta	74 W	75 Re	76 Os	77 Ir	78 Pt	79 Au	80 Hg	81 Tl	82 Pb	83 Bi	84 Po	85 At	86 Rn
7	87 Fr	88 Ra	**	89 Ac	104 Rf	105 Db	106 Sg	107 Bh	108 Hs	109 Mt	110 Ds	111 Rg	112 Cn	113 Uut	114 Fl	115 Uup	116 Lv	117 Uus	118 Uuo

*Lanthanoids			*	58 Ce	59 Pr	60 Nd	61 Pm	62 Sm	63 Eu	64 Gd	65 Tb	66 Dy	67 Ho	68 Er	69 Tm	70 Yb	71 Lu
**Actinides			**	90 Th	91 Pa	92 U	93 Np	94 Pu	95 Am	96 Cm	97 Bk	98 Cf	99 Es	100 Fm	101 Md	102 No	103 Lr

Grupos

Alkali metals
Alkaline earth metals
Chalcogens or oxigen group
Crystallogens or carbon group
Noble gases
Halogens
Transition metals
Lanthanoids and actinides
Pnictogens or nitrogen group
Icosagens or boron group

Bohr model

[zoom]

Element

Symbol

Atomic form

Atomic weight

Num electrons (Z)

Num protons (Z)

Num neutrons (A-Z)

Electronic configuration

Group

Documentation

Periodic table

Throughout the nineteenth century numerous elements were discovered and it was found that they had similar physical and chemical properties. This encouraged scientists to try to classify and sort them in any way that would group these elements into families according to their properties.

In 1869, the Russian scientist Dmitri Mendeleev and, in 1870, German scientist Lothar Meyer created his famous periodic table.

In this first periodic table, the 63 known elements were ranked in order of increasing atomic mass. Both scientists had the brilliant idea of leaving gaps were future elements, undiscovered up to that moment, could be located (at present, 118 elements are known). In other cases, they were forced to reverse the position of some elements to get them grouped into the corresponding family attending to their properties.

Years later, in 1914, the British scientist Henry Moseley discovered a method to empirically determine the atomic number of the elements (number of protons in an atom, Z). He took advantage of his idea to classify the periodic table in order of increasing atomic number and appreciated that every element was in the right place according to their properties. This classification is the one that continues in use today.

Electronic configuration

The electronic configuration of an element is the distribution of electrons of its atoms in orbitals of different energy levels.

The guidelines for determining the electron configuration of an element’s atom are:

The number of electrons in a neutral atom coincides with the atomic number (the number of positive charges, protons, must match the number of negative charges, electrons).
Electrons are placed on the atoms in the order of ascending energy determined by the the Moeller diagram.

The table rows are called periods and the columns are called groups.

Elements in the same period have the same number of energy levels of electrons; these electron shells can be full or not.

The elements of a group have the same electronic structure at their outermost level and therefore have similar chemical properties.

Periodic properties of the elements

Observation of the Periodic Table shows that in each period, the number of electrons in the last layer of atoms varies between one and eight, and when moving from one period to the next this configuration repeats.

As much of the physical and chemical properties of elements depend on the electronic distribution of its last level, it is logical that such properties vary periodically depending on the atomic number. Among these properties that vary periodically we can study: atomic volume, atomic radius, ionic radius, ionization energy, electron affinity and electronegativity.

Did you know?

Dmitri Mendeleev, the scientist creator of the periodic table, was the youngest of 17 siblings. Henry Moseley, a scientist who put the elements in order of increasing atomic number, died very young (in Gallipoli, Italy) during World War II.

Despite being placed in order of increasing atomic number, it also agrees that the elements also follow an order of increasing atomic mass. However, there are four pairs of elements that, following the current order, do not verify the increasing atomic mass, that is, the rear element has a lower atomic mass than the preceding one. These four pairs are formed by argon-potassium, cobalt-nickel, tellurium-iodine and thorium-protactinio.

Out of this 118 elements, 92 are naturally occuring and rest were created in labs by scientists (artificial or man-made elements). About 70 elements are part of living beings (essential or primary elements like carbon, oxygen, hydrogen and sulfur, secondary elements such as calcium, sodium, potassium or magnesium and trace elements such as iron, copper, chromium or iodine). Only 3 of them have been discovered by Spanish scientists: platinum, discovered by Antonio Ulloa in 1748; wolfram, discovered by the Elhuyar brothers in 1783 and Vanadium discovered by Andrés Manuel del Río in 1801.

The origin of the names of the chemical elements is referred to research centers, distinguished scientists, celestial bodies, geographic locations, minerals, mythological names and even diverse superstitions:

As examples of famous scientists, we have the einstenio (in honour of Albert Einstein), nobelium (in honour of Alfred Nobel) and mendelevium (named after Dmitri Mendeleev himself).
Regarding celestial bodies, we find mercury (due to the planet of the same name), uranium (due to the planet Uranus) or plutonium (the dwarf planet Pluto).
Examples of geographic locations, there are names of countries such as germanium, francium or polonium (name with which the Curies wanted to claim the freedom of the country of origin of Marie Curie), as well as names of cities and continents such as europium, americium or californium.
As examples of mythological names, we can find thorium (named after Thor, the Norse god of war) or promethium (in honour of Prometheus, titan god who stole fire from Mount Olympus gave it to mankind).

We do not know how many elements we will be able to synthesize in the laboratory ... Richard Feynman predicted that the periodic table would be completed with 137, although recent research reduced the number to 126. This element tried synthesized once unsuccessfully at CERN (1971). It has not been possible to synthesize yet, but already baptized with the name Unbihexium.