Oxidation Number vs Charge
Different elements in the periodic table exhibit different chemical and physical characteristics. And when they join to form molecules, different elements join with other elements in different proportions. Among a large number of variations between elements, the most simple and important parameters are their charge and oxidation number. Charge and oxidation number of an element helps to identify, to which group this element belongs in the periodic table. Most importantly it helps to describe the element’s ability to form other molecules, coordination compounds and thus helps to identify their empirical formulas. Other than these, charge and oxidation number tells us about many properties of the elements.
Charge of any atom is zero. When atoms remove or obtain electrons, they gain a charge. Atoms do this in order to fill their valance shell according to the octet rule. In an atom, the number of protons and electrons are in similar numbers. Protons are said to be positively charged, whereas electrons are negatively charged. So when electrons from the valence shell are removed the atom forms a positive charge ion, because the number of positive protons is higher than the number of electrons in that ion. When an atom is more electro negative, it can attract electrons from other atoms towards itself. When this happens, they gain more electrons than the number of protons resides in their nucleus, thus the atoms become negative ions. The number of electrons donated or abstract differs from atom to atom. This can be predicted from the position of the element in the periodic table. Normally, the same group atoms will form the same charged ions, because they have the same number of valence electrons. The group number also shows the number of valence electrons; therefore, we can determine the charge of the ions in that group. For example, group one elements form monovalent (+1) charged ions. Group two elements form divalent positively charged ions. Group three and group four atoms form +3 and +4 charged ions accordingly. From group five to group seven, atoms make negatively charged ions, because it is easier to fill their valence electrons by just getting 2 or 3 electrons rather than emitting five, six or seven electrons. So group five elements make -3 charged ions, whereas group 6 elements make -2 ions and group 7 elements make -1 ions. Other than these simple charged ions, there are also compound ions with charges like NH4+ and CO32-etc.
Oxidation number is a characteristic of the central atom of a coordination compound. Sometimes the charge and the oxidation number are similar, but sometimes it is different. For instance, the simple s block and p block elements have the same oxidation number as their charge. Also, polyatomic ions have the same oxidation number as the charge. Same element can have different oxidation numbers, depending on the other atoms it is connected with. In a free element, oxidation number is always zero. Transition metal ions (d block), elements have different oxidation numbers.
What is the difference between Charge and Oxidation Number?
• Charge of an atom in a molecule is determined by considering all the electrons that are shared equally in a bond between two or more atoms.
• Oxidation number is the charge, an atom would have, if the more electronegative atom gained both electrons in a bond.
• So if, all the ligands in a coordination compound are removed heterolytically, the remaining number of electron in the central atom will give its oxidation number.