An element is a pure chemical substance characterized by one type of atom of the same atomic number. Elements are categorized in the periodic table, by having their atomic numbers placed in ascending order. Then, they are further categorized into groups and rows, where groups represent elements with the same number of valence electrons, while rows represent elements with the same number of electron shells.
For example, carbon has 6 protons within its nucleus and 6 electrons within the electron cloud. In the periodic table, since atomic number is ascending, it is placed in after the element Boron, which has 5 protons, and before Nitrogen, which has 6 protons. Carbon is placed within the second row, along with other elements such as Boron and Nitrogen because all these elements possess two main electron shells. Furthermore, it is placed in Group IV in the periodic table because it has 4 valence electrons. Other elements within the same group, such as Silicon, and Germanium also have 4 valence electrons, but are in lower rows because they possess more electron shells.
Elements within the same group within the periodic table usually have the same properties, even if they have a different number of electron shells, as the number of valence electrons determines the overall behavior of that element. For example, Lithium and Sodium have the same or similar chemical properties as they both only have one valence shell electron. Thus, understanding the nature of elements and the categorization technique of the periodic table is critical for understanding different chemical phenomena.