The periodic table arranges elements in order of increasing atomic number and groups them based on recurring chemical properties. Elements in the same group have the same number of valence electrons, which are the electrons in the outermost shell and are crucial in chemical reactions. For example, all Group 1 elements (alkali metals) have one valence electron in an s orbital. This similarity in valence electron configuration results in similar chemical behaviors. The electron configurations of elements thus reveal the underlying structure of the periodic table and explain the periodicity of elemental properties. 1. Elements in the same group of the periodic table have the same number of which type of electrons? Core electrons f orbital electrons d orbital electrons Valence electrons 2. An element has the electron configuration [Ne]3s23p5 . To which group does it belong? Group 18 (Noble Gases) Group 17 (Halogens) Group 16 (Chalcogens) Group 15 (Pnictogens) 3. Which of the following elements has five valence electrons? Neon (Ne) Nitrogen (N) Sodium (Na) Magnesium (Mg)