A stable compound with a complete octet or electronic configuration
Explanation:
The Periodic table is the arrangements of chemical elements in horizontal rows (called 'Periods') and vertical columns (called 'Groups') based on their various physical and chemical properties.
Elements in the same group have a common quality being that they have the same number of free (valent) electrons in their outermost shell. For example, elements in group 1 all have one valent electron in the outermost shell as compared to elements in group 5 which have five valent electrons in the outermost shell. Therefore the group number tells us the number of valence electrons of all the elements in that group.
Meanwhile, elements in the same period have the same number of outermost shell but an increasing number of valence electrons as one goes across the period from left to right.
Elements form chemical bonds in an effort to achieve chemical stability. Chemical stability is achieved when the shells of the elements are fully filled with electrons and achieved a stable electronic configuration of 2 or 8.
The type of bonds formed depend on the number of valence electrons available for bonding in the outermost shell of the element.
So the element Oxygen for example which has 6 valence electrons, in its outermost shell tends to form covalent bonds (a bond achieved by sharing electrons). It is easier for oxygen to form a covalent bond by sharing its valence electrons with another element than to lose all six valence electrons in order to achieve a stable octet state
The element Chlorine (Cl, with seven valence electrons) on the other hand tends to form electrovalent or ionic bonds by accepting an electron from a metal element like Sodium (Na) to achieve a complete octet. It is easier for Cl to achieve a stable octet state by accepting an electron than losing all 7 valence electrons.
Therefore, the group number (an indicator of the number of valence electrons in the outermost shell) plus the number of bonds formed equals a stable atom or compound with a complete electronic configuration.
