In the modern periodic table, elements are arranged by atomic number. They are placed with the lowest atomic number first, and elements with increasing atomic numbers run to the right. They are also arranged in vertical ... More »

The modern periodic table is arranged in ascending order according to atomic number. An element's atomic number is equal to the number of protons in each atom. Within this order, elements are arranged into distinct group... More »

An element is a substance composed of only one type of atom. There are more than 100 known elements, all of which are arranged according to their properties on the Periodic Table of the Elements. More » Science Chemistry Atoms & Molecules

The Roman numerals on a periodic table of elements define the chemical group of the elements in that column and identify the number of valence electrons of each element. Group IA elements have one valence electron; group... More »

Periodic law, also known as Mendeleev's law, is the concept that the chemical and physical properties of elements are based on an element's atomic weight when arranged by increasing periodic atomic number. Periodic law w... More »

The heaviest metal on the periodic table of elements is osmium. Its density is 22.57 grams per cubic centimeter, which is twice that of the element lead. A quarter-gallon of osmium weighs 50 pounds when compared to a qua... More »

Three elements on the periodic table are magnetic: iron, nickel and cobalt. There are also a number of metals that take on slight magnetic properties when subjected to a magnetic field. More » Science Chemistry Atoms & Molecules