What is the atomic mass of magnesium?

History of the Periodic Table

In 1869, a Russian chemist named Dmitri Mendeleev was the first to publish a periodic table similar to the one we use today. It’s said that he used to play a kind of solitaire on long train rides using cards with information about the elements written out on them. This helped him figure out how to group the elements together in a chart. You can see Mendeleev’s original table here.

You can see an interactive version of the periodic table we use today here. Watch videos about every element in the periodic table!

Mendeleev periodic table • PBS periodic table • periodic videos

The atoms that make up all known elements are organized on a chart called the periodic table of elements. It is organized in a grid, with rows and columns. You can use the large periodic table on page 117 as a reference for the rest of the book. Each element on the periodic table is located in a specific square based on its atomic structure and characteristics. Each square displays certain information about that element, including its element name, symbol, atomic number, and atomic mass. Every element is represented by one or two letters called its atomic symbol. For example, the element lithium’s atomic symbol is Li, while the element carbon’s atomic symbol is C. Iron is Fe. Every element also has an atomic number. For example, lithium’s atomic number is 3. Carbon’s is 6. The periodic table lists elements in the order of their atomic number, from left to right and top to bottom. An element’s atomic number tells you how many protons are in that atom’s nucleus. In a lithium atom, which has an atomic number of 3, there are three protons. In a carbon atom, there are six protons. Because neutral atoms have the same number of protons and electrons, an element’s atomic number can also tell you how many electrons it has. Therefore, a lithium atom also has three electrons and a carbon atom has six electrons. Each square on the periodic table also shows the element’s average atomic mass. Elements are so tiny that it does not make sense to measure them in kilograms or even grams. Scientists use a unit of measurement called an amu (atomic mass unit) to measure the mass of an atom.