the number of valence electrons in an atom of an element is equal to the group number
Valence electron The number of valence electrons of an element can be determined by the periodic table group (vertical column) in which the element is categorized. With the exception of groups 3â€“12 (the transition metals), the units digit of the group number identifies how many valence electrons are associated with a neutral atom of an element listed under that particular column.
Isotope The number of protons within the atom's nucleus is called atomic number and is equal to the number of electrons in the neutral (non-ionized) atom. Each atomic number identifies a specific element, but not the isotope; an atom of a given element may have a wide range in its number of neutrons. The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number.
Main-group element Main-group elements (with some of the lighter transition metals) are the most abundant elements on Earth, in the Solar System, and in the Universe. They are sometimes also called the representative elements.
Van der Waals equation is the volume of the container occupied by each particle (not the velocity of a particle), and k is the Boltzmann constant. It introduces two new parameters: a', a measure of the average attraction between particles, and b', the volume excluded from v by one particle.