Development System Periodic Element Effort for grouping elements to in groups certain actually already done para expert since formerly, but grouping period that still simple. Grouping which most simple is share element to in group metal and nonmetal. Along development knowledge chemistry, business grouping elements Which increasingly this is done by experts on various grounds grouping Which different, but objective Finally The same, that is make it easier in learn traits element. Started on year 1829, John Wolfgang Dobereiner grouping elements Which very similar its nature. It turns out that each group consists of three elements, so it is a group it's called a triad . If the elements in a triad are arranged according to increase mass atom relatively speaking, it turns out mass atom nor traits element the second is an average of relative atomic masses and properties element First And third. Example Grouping Characteristic Element Triads A r Average A r Element First And Third Being Chlori ne Bromin e Iodine 35.5 79.9 127 35.5 127 81, 2 2 Gas Liq uid Congested System triads This it turns out There is its weakness. System This not enough efficient Because It turns out that there are several other elements that are not included in a triad, however have traits similar with triads the. Business furthermore done by a expert chemistry origin English named A. R. Newlands, who in 1864 announced his discovery of called law octave . Newlands compile element based on increase mass atom relative. It turns out element Which disagree 1 octave (element number 1 And 8th, the 2nd element and the 9th element), show similar properties. This octave law also has the weakness because it only applies to light elements. If we continue, it turns out that the similarities in character are too forced. For example, Zn have characteristic Which Enough different with Be, Mg, And Ca. The following is the table contains part of Newlands octave list. Part List Octave Newlands Do Re Mi Fa Sol La Si 1 2 3 4 5 6 7 H Li Be B C N O F Na Mg Al Si P S Cl K Ca Cr Ti M N Fe Co, Ni Cu Zn Y In US Se Then in 1869, a Russian scholar named Dmitri Ivanovich Mendeleev , based on his observations of 63 elements Already known when That, conclude that traits element is function periodic from mass atom relative And equality characteristic. It means, If element- Elements are arranged in order of increasing relative atomic mass, hence certain properties will repeated in a way periodic. Mendeleev put elements, which have similarity characteristic in One lane vertical, Which called group . Lanes hori- zonal, that is lane elements based on increase mass atom relatively speaking, called period. System periodic Mendeleev This have weakness And Also superiority. The weakness of this system is placement a number of element No in accordance with increase mass atom relative. Besides That Still Lots element Which Not yet known.
Approximately 45 years later, to be precise in 1914, Henry G. Moseley (1887 – 1915) find that order element in system periodic in accordance with increase number atom element. Placement tellurium ( Ar _ = 128) And iodine ( Ar _ = 127) Which No in accordance with increase mass atom relatively, it turns out in accordance with increase number the atom (number atom Te = 52; I = 53). So, characteristic periodic more appropriate said as function number atom. System periodic element modern arranged based on increase number atom And similarity of traits. The modern periodic system of elements is a refinement from system periodic Mendeleev.