2. John Newlands, Dmitri Mendeleev & Henry Moseley worked to the development of the periodic table. In the periodic table, elements are organized by the atomic number. The rows of the periodic table are called “periods” & the columns are called “groups”. Elements in the same period share the same energy levels & elements in the same group have the same number of valence electrons.

3. The main groups are alkali metals, alkaline-earth metals, halogens and noble gases. Helium is a group of it’s own. Most of these elements are metals.

4. Trends common in the periodic table are related to the atomic structure of an element. Energy generally increases as you move across a period & decreases as you move down a group. The radius of an atom and the ionic size decreases as you move across a period & increases as you move down a group.

5. 93 natural elements were formed in the interior of stars. Synthetic elements, which are elements whose atomic number is greater than 93, are formed by using particle accelerators. In which is shown to the below.