One electron each comes from H, H, Cl, and Cl atoms: 1s1 of each H and 3pz1 of each Cl. Each of these hybrid orbitals has one electron and can accept one more. These four orbitals hybridize together to form four identical sp3 orbitals, all of which have the same energy. 2s, 2px, 2py, and 2pz orbitals of carbon are now half-filled. Let us look at the ground state electronic configuration of each atom in CH2Cl2 in terms of the orbitals.Ĭarbon, in the excited state, has one of the 2s electrons promoted to 2p therefore, the electronic configuration becomes 1s22s22px12py12pz1. The formula for the formal charge is as follows.įormal charge (FC) = Valence electrons – 0.5*bonding electrons – non-bonding electronsįor carbon, FC = 0 for hydrogen, FC = 0 and for Cl, FC = 0.Ī bond is formed between two atoms by the virtue of the overlap of orbitals on two atoms as these orbitals share electrons. Let us calculate the formal charges on each of the constituent atoms. The molecule is neutral, i.e., there is no charge on it. Simultaneously, both hydrogen atoms will achieve their respective duplets, and both chlorine atoms will achieve their respective octets, and thereby the situation will be a win-win for all five atoms.Ĭarbon will be singly bonded to H, H, Cl, and Cl, as shown in the Lewis structure. Two hydrogen atoms and two chlorine atoms can help carbon achieve this feat! Carbon needs 4 more electrons for its octet to be complete. Now, we shall construct a skeleton of the molecule with carbon as the central atom. In CH2Cl2, carbon satisfies this condition (4 electrons short of the octet versus 1 for chlorine). The central atom is the one that has the highest bonding capacity it is the atom that is the shortest of the octet. Next, we shall figure out the central atom to which the rest of the atoms shall be bonded. The number of valence electrons is therefore 7, and hence Cl needs 1 more to achieve the octet. K shell has 2 electrons, L shell has 8, and M shell has 7 electrons. Similarly, the atomic number of hydrogen is 1 thus, each H has 1 electron and needs 1 more to achieve the duplet. To achieve the octet, carbon needs 4 more electrons. Thus, the number of valence electrons is 4. There are 2 electrons in its K shell and 4 electrons in the L shell. The atomic number of carbon is 6 therefore, it possesses 6 electrons in its neutral form. We shall start by calculating the number of valence electrons in each atom of CH2Cl2 in order to see how short an atom is from an octet (or duplet in the case of hydrogen). Let us take a look at the chemical bonding represented by Lewis structure in CH2Cl2. Hydrogen, however, does tend towards a duplet, not octet, because it has only one electron in its K shell, and thus needs only one more to achieve the maximum capacity of the K shell. Please note that several atoms follow the octet rule, i.e., they tend to achieve eight electrons in their valence shell through chemical bonding this is reflected in the Lewis structure of the molecule. The structures drawn using this theory are termed Lewis (dot) structures. The purpose of this theory is to help visualize the chemical bonding of atoms in molecules.Įlectrons are represented as dots, and each pair of bonding electrons between two atoms is shown as a line. The Lewis theory of chemical bonding-although quite primitive and the most limited theory on electronic structure-does help one to determine how valence electrons are arranged around the constituent atoms in a molecule.
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