Electropositive or electronegative nature of elements

METALS:

From the electronic viewpoint, metals are defined as elements which form positive ions by losing electrons. They contain 1, 2 or 3 valence electrons. For example, a sodium atom loses 1 electron, a calcium atom loses 2 electrons and an aluminum atom loses 3 electrons, to form the respective positively charged ions (Na+1, Ca+2, Al+3).

NON-METALS:

They are defined as elements which form negative ions by gaining electrons. They contain 5, 6 or 7 valence electrons. For example, chlorine contains 7 valence electrons and gains 1 electron to form a negatively charged chloride ion (Cl–1). Oxygen contains 6 valence electrons and gains 2 electrons to form the negatively charged oxide ion (O–2).

METALLOIDS:

Elements with 4 valence electrons are normally metalloids. The noble gases with 8 valence electrons do not form ions and cannot really be classified as metals or non-metals. However, since they are gases they show the physical characteristics of gases.