The tricky part in constructing the table is knowing when they cut off - or, equivalently, how many columns (groups) to include in each row. They list the elements in order of atomic number before cutting off and continuing again in a new row, repeating established patterns of chemical properties. Rows in the periodic table are called periods, and we currently have seven. The noble gases, in the last column, are so named because they’re holding about all the electrons they can, so they don’t react easily with other elements - just as the noble houses of old. The first group, known as the alkali metals, has just one such electron, easy to lose when reacting with an element that has more electrons, such as one from the 17th group, the halogens. Roughly speaking, the farther to the right a group is, the more electrons it has ready to interact with other elements. If the symbol doesn’t match the name (as in Au for gold and Na for sodium), it’s likely based on the element’s original Latin name (aurum and natrium).Įlements in the same column often share similarities, so chemists call these groups.
Sometimes they list the full name of each element, but often only include their one- or two-letter symbol, nicknames that make complicated chemical formulas more compact. Many periodic tables include the atomic number (number of protons) and atomic weight (which depends on protons and neutrons).