The periodic table is arranged by various patterns. Identify two patterns and give examples of both patterns.
Two patterns in the arrangement of the periodic table are the periods and the groups.
1. Periods: The periodic table is organized into periods, which are rows running horizontally. Each period represents a different energy level or electron shell in an atom. As you move from left to right within a period, the atomic number (number of protons) increases by one. For example, the second period (row) in the periodic table includes elements such as lithium (atomic number 3), beryllium (atomic number 4), boron (atomic number 5), carbon (atomic number 6), nitrogen (atomic number 7), and so on.
2. Groups: The periodic table is also arranged into groups, which are columns running vertically. Elements within the same group share similar chemical properties, as they have the same number of valence electrons. The group number corresponds to the number of valence electrons in the elements of that group. For instance, Group 1 (also known as Alkali Metals) contains elements like lithium (Li), sodium (Na), potassium (K), which all have one valence electron. Group 17 (Halogens) consists of elements like fluorine (F), chlorine (Cl), bromine (Br), where all have seven valence electrons.