How many elements are in the periodic table? Who created the periodic table? What are two metalloids? How many metals are there?

How many elements are in the periodic table? Who created the periodic table?
What are two metalloids? How many metals are there?

Expert Answers
mvcdc eNotes educator| Certified Educator

The periodic table is a systematic arrangement of chemical elements, ordered by their atomic numbers and hence electron configuration. Various properties can be generalized simply based on the periodic table. There are trends in atomic size, ionization energy, electron affinity, and metallic property. These properties result from the electronic properties of elements, and are a natural consequence of their periodic arrangement.

While he was not the first to create a table of elements, Dmitri Mendeleev often gets credit for the first periodic table. Mendeleev arranged the elements in order of increasing atomic weights, and what is unique about his periodic table is that he left blanks for elements that weren't discovered during his time, but that he believed to exist based on properties of known elements and patterns arising from his table. Upon discovery of the nucleus—protons and neutrons—and further discoveries in quantum mechanics, the periodic table was revised to reflect an order by atomic number instead of by weight.

The periodic table is divided into various categories—outermost valence shell (which includes s, p, d, and f block elements) or metallic property. Metals are toward the left side of the periodic table and non-metals toward the right. An exception is hydrogen, which is put on the first column due to other properties, such as its tendency to form a +1 ion just like the others in that column. Metalloids are semi-conductors with both metallic and non-metallic properties and sit in between these two groups in a diagonal that includes boron and silicon. The current periodic table has eight metalloids. The number of metals and non-metals cannot be stated, as some elements with higher atomic numbers have not been thoroughly characterized yet. Following the trends, of the 118 elements, 92 must be metals, with the rest being either non-metals or metalloids.

In very recent times, four of the heavy elements—113, 115, 117, and 118—have been properly confirmed and named.

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