Outer electronic configuration of Ni +2 = 3d 8 X + 4(-1) = -2 ( ∵ CN - has -1 negative charge)Įlectronic configuration of Ni is: 3d 84s 2Įlectronic configuration of Ni +2 = 3d 8 Using overall charge balance as the whole ion has overall -2 charge: In 2-, oxidation state of Ni can be calculated as : Because each chlorine has one bond and six lone pair electrons (1 + 6 = 7) in this diagram and seven valence electrons, it also has no charge.According to the valence band theory, the central metal atom or ion under the influence of ligands can use its (n-1)d, ns, np (inner orbital complex) or ns, np, nd (outer orbital complex)orbitals for hybridisation to form equivalent set of orbitals of definite geometry. Because it normally has four valence electrons, carbon has no charge (4 - 4 = 0). In our example, CCl 4, carbon has four bonds around it. Once you've determined the charge on an atom, write it next to the atomic symbol of that atom. Subtract this number from the number of valence electrons the atom is expected to have (which you already figured out in Step 1) to calculate its charge. The completed Lewis structure for CCl4 is shown in the following figure:Ĭheck to see if any of the atoms in the molecule have a positive or negative charge.Īdd the number of lone pair electrons to the number of bonds for each atom in the molecule. Since chlorine wants eight electrons, three pairs need to be added to each. Since carbon wants eight electrons, it doesn't require lone pairs.Įach chlorine, on the other hand, has only one bond for a total of two electrons. The four bonds around it contain eight electrons. Let's take a look at the carbon atom in our diagram. In this structure, both carbon and chlorine follow the rules for the number of bonds each wants.Īdd lone pairs of electrons to each atom until each atom is surrounded by the number of electrons we said they wanted in step 2.

Between the carbon and each chlorine atom is a single chemical bond, totaling four. In our example, CCl 4, there are fewer carbon atoms than chlorine atoms, so the carbon atom goes into the middle of the molecule, with four chlorine atoms arranged around it. Boron usually bonds three times in uncharged molecules and four times when present in a polyatomic ion.Carbon's family usually bonds four times.Nitrogen's family bonds three times in uncharged molecules and two, three, or four times when present in polyatomic ions.Oxygen's family bonds twice in uncharged molecules and one, two, or three times when present in polyatomic ions.

In our example, we can assume that carbon will probably be in the center of the molecule.

The atom that's least abundant in the compound is usually in the middle of the molecule.

Unfortunately, randomness rarely yields the right answer, so we'll need some rules to help us out. In this step, it's tempting to just randomly stick atoms and bonds wherever you can until everything is stuck together. In our example, 8/2 = 4 bonds.Īrrange the atoms so the molecule has the same number of covalent bonds that you found in step 4. Problem 1: Draw the Lewis structures for the following molecules or polyatomic ions:ĭivide the number of bonding electrons by two to find the number of bonds.īecause there are two shared electrons in every covalent bond, dividing the bonding electrons by two can be used to find the number of chemical bonds.

All other atoms want eight octet electrons.

Boron wants six octet electrons for neutral molecules and eight for molecules with charge.

The number of octet electrons that atoms want can usually be determined by the following rules: The number of 'octet electrons' is equal to the number of valence electrons that each atom will have when they have the same electron configuration as the nearest noble gas (the octet rule). You won't find the term 'octet electron count' in any textbook because, as far as I know, I made it up. For example, NH 4 + will have one fewer valence electron that the nitrogen and four hydrogens would have because it has a +1 charge.Ĭount the total octet electron count in the molecule. To do so, subtract the ionic charge from the valence electron count. Occasionally, you'll have to find the Lewis structure for a polyatomic ion. Therefore, the number of valence electrons for this molecule is 4 + (4 × 7) = 32. The single carbon atom contains four valence electrons, and each of the four chlorine atoms contains seven valence electrons. Lewis structures (named for chemical theorist Gilbert Newton Lewis) are pictures that show all of the valence electrons and atoms in a covalently bonded molecule.Ĭount the total number of valence electrons in the molecule.Īs an example, let's use carbon tetrachloride, CCl4.

Cl4 ion bonding