Periodic table

Periodic table history

History of the periodic table of chemical elements

1669 German merchant and amateur alchemist Hennig Brand attempted to created a Philosopher’s Stone; an object that supposedly could turn metals into pure gold. He heated residues from boiled urine, and a liquid dropped out and burst into flames. This was the first discovery of phosphorus.

In 1680 Robert Boyle also discovered phosphorus, and it became public.

In 1809 at least 47 elements were discovered, and scientists began to see patterns in the characteristics.

In 1863 English chemist John Newlands divided the then discovered 56 elements into 11 groups, based on characteristics.

DIMITRI MENDELEEV

1869 Russian chemist Dimitri Mendeleev started the development of the periodic table, arranging chemical elements by atomic mass. He predicted the discovery of other elements, and left spaces open in his periodic table for them. In 1886 French physicist Antoine Bequerel first discovered radioactivity. Thomson student from New Zealand Ernest Rutherford named three types of radiation; alpha, beta and gamma rays. Marie and Pierre Curie started working on the radiation of uranium and thorium, and subsequently discovered radium and polonium. They discovered that beta particles were negatively charged. In 1894 Sir William Ramsay and Lord Rayleigh discovered the noble gases, which were added to the periodic table as group 0. In 1897 English physicist J. J. Thomson first discovered electrons; small negatively charged particles in an atom. John Townsend and Robert Millikan determined their exact charge and mass. In 1900 Bequerel discovered that electrons and beta particles as identified by the Curies are the same thing. In 1903 Rutherford announced that radioactivity is caused by the breakdown of atoms. In 1911 Rutherford and German physicist Hans Geiger discovered that electrons orbit the nucleus of an atom. In 1913 Bohr discovered that electrons move around a nucleus in discrete energy called orbitals. Radiation is emitted during movement from one orbital to another. In 1914 Rutherford first identified protons in the atomic nucleus. He also transmutated a nitrogen atom into an oxygen atom for the first time. English physicist Henry Moseley provided atomic numbers, based on the number of electrons in an atom, rather than based on atomic mass. In 1932 James Chadwick first discovered neutrons, and isotopes were identified. This was the complete basis for the periodic table. In that same year Englishman Cockroft and the Irishman Walton first split an atom by bombarding lithium in a particle accelerator, changing it to two helium nuclei. In 1945 Glenn Seaborg identified lanthanides and actinides (atomic number >92), which are usually placed below the periodic table.

MODERN PERIODICTABLE

Reading the table

The periodic table contains an enormous amount of important information:  

Atomic number: The number of protons in an atom is referred to as the atomic number of that element. The number of protons defines what element it is and also determines the chemical behavior of the element. For example, carbon atoms have six protons, hydrogen atoms have one, and oxygen atoms have eight.

Atomic symbol: The atomic symbol (or element symbol) is an abbreviation chosen to represent an element ("C" for carbon, "H" for hydrogen and "O" for oxygen, etc.). These symbols are used internationally and are sometimes unexpected. For example, the symbol for tungsten is "W" because another name for that element is wolfram. Also, the atomic symbol for gold if "Au" because the word for gold in Latin is aurum. 

Atomic weight: The standard atomic weight of an element is the average mass of the element in atomic mass units (amu). Individual atoms always have an integer number of atomic mass units; however, the atomic mass on the periodic table is stated as a decimal number because it is an average of the various isotopes of an element. The average number of neutrons for an element can be found by subtracting the number of protons (atomic number) from the atomic mass.

Atomic weight for elements 93-118: For naturally occurring elements, the atomic weight is calculated from averaging the weights of the natural abundances of the isotopes of that element. However, for lab-created trans-uranium elements — elements with atomic numbers higher than 92 — there is no "natural" abundance. The convention is to list the atomic weight of the longest-lived isotope in the periodic table. These atomic weights should be considered provisional since a new isotope with a longer half-life could be produced in the future.

Within this category are the superheavy elements, or those with atomic numbers above 104. The larger the atom's nucleus — which increases with the number of protons inside — the more unstable that element is, generally. As such, these outsized elements are fleeting, lasting mere milliseconds before decaying into lighter elements, according to the International Union of Pure and Applied Chemistry (IUPAC). For instance, superheavy elements 113, 115, 117 and 118 were verified by the IUPAC in December 2015, completing the seventh row, or period, on the table. Several different labs produced the superheavy elements. The atomic numbers, temporary names and official names are:

• 113: ununtrium (Uut), nihonium (Nh)
• 115: ununpentium (Uup), moscovium (Mc)
• 117: ununseptium (Uus), tennessine (Ts)
• 118: ununoctium (Uuo), oganesson (Og)

 Block 

S

P

D

F

What Are the S-Block Elements?

If the periodic table were a city, the s-block would be a small neighborhood filled with extremely similar houses and properties. Within the periodic table, the s-block is located to the far left and includes all of the elements in the first two columns (columns 1 and 2) plus helium, which is located in the top right corner in column 8A (column 18 on some versions of the periodic table). In the periodic table below, the s-block is colored pink.

The s-block elements are the 14 elements contained within these columns. All of the s-block elements are unified by the fact that their valence electrons (outermost electrons) are in an s orbital. The s orbital is spherical and can be occupied by a maximum of two electrons. Elements in column 1 have one electron in the sorbital, and elements in column 2 (plus helium) have two electrons in the s orbital.

The s-block elements include hydrogen (H), helium (He), lithium (Li), beryllium (Be), sodium (Na), magnesium (Mg), potassium (K), calcium (Ca), rubidium (Rb), strontium (Sr), cesium (Cs), barium (Ba), francium (Fr) and radium (Ra). The periodic table shows exactly where these elements are within the s-block.

Properties of S-Block Elements

If the elements were houses in our hypothetical s-block neighborhood, they would be very uniform, each one only slightly different than the other. This is markedly different compared to the other neighborhoods on the periodic table, which have a wider variety of houses in many shapes, sizes and colors.

All of the s-block elements are metals. In general, they are shiny, silvery, good conductors of heat and electricity and lose their valence electrons easily. In fact, they lose their trademark s orbital valence electrons so easily that the s-block elements are considered to be some of the most reactive elements on the periodic table.

Sodium, an s-block element, is a silvery and soft metal.

The elements in column 1, known collectively as the alkali metals (except hydrogen), always lose their one valence electron to make a +1 ion. These metals are characterized by being silvery, very soft, not very dense and having low melting points. These metals react extremely vigorously with water and even oxygen to produce energy and flammable hydrogen gas. They are kept in mineral oil to reduce the chance of an unwanted reaction or worse, an unwanted explosion.

Like a few other elements in the s-block, potassium reacts energetically with water.