SP2 Lewis Structure: Drawings, Hybridization, Shape, Charges, Pair And Detailed Facts


 Several theories have been proposed to describe the sp2 Lewis structure. Here we will be making a note on how Lewis’s structure has provided a satisfactory explanation regarding chemical combination of sp2 hybridized atoms.

Lewis structure formation functions on the basis of octet rule and only outermost valence electrons are considered. The possible shape of sp2 hybridized compound can be trigonal planar. Formal charge is a computation to be aware of the charge of atom in Lewis structure and one nonbonding electron pair is in sp2 hybrid.

The sp2 hybridized orbitals overlap forming σ bonds and remaining P orbitals overlap to form π bonds. The resonance of a sp2 hybridized compound is having more than one Lewis structure to explain the properties of a molecule. All the sp2 hybridized covalent compounds show polarity. If the net dipole moment of a compound is zero than it is non polar and if it is non zero than it is polar.

If you are curious about how Lewis’s octet rule theory helped out in determining the cause of chemical combination of atoms which left a huge impact in the study of chemistry.

Let’s discuss about the facts in detail.

SP2 Lewis structure octet rule

SP2 Lewis structure theory functions on the basis of octet rule. As this thesis is rooted on the electronic configuration of atoms and therefore is also realized as “Electronic Theory of Chemical Bonding”.

sp2 lewis structure
sp2 lewis structure of formaldehyde

Octet Rule

This rule states that atoms of various elements undergo chemical combination to attain an eight electrons (octet of electrons) configuration in their valance shell.

The chemical combination is taken place by mutual sharing of electrons between the atoms and thus bonds are formed. This bond is called Covalent Bond.

E.g.; –sp2 Lewis’s structure of formaldehyde (H2CO) can be represented as

Here carbon atom has 4 electrons in the outer most shell and requires 4 more electrons to attain its octet. Thus, when carbon atom combines with the surroundings 2 hydrogen atoms shares 1 each electrons forming single bonds and combine with 1 oxygen atom sharing 2 electrons and form a double bond thus completing its octet.

Here the sp2hybridized orbitals to form 2 C-H and 1 C-O bond and the remaining unhybridized orbitals form C = O π bond.

Limitations of Octet Rule for sp2 hybridized compounds

Formation of molecules with incomplete Octet

In the case of covalent compounds of Be, B, Al etc. The central atoms have electrons lesser than eight in its outmost shell and hence does not obey octet rule.

E.g.: – BF3 compound.

SP2 Lewis structure of BF3

The valance of Boron is 3 and they are shared with 3 Fluorine atoms to form BF3. Thus, Boron gains only 6 electrons and not 8. Thus, neglecting the octet rule.

SP2 hybridization:

  • Here in sp2 hybridization one’s orbital and 2 p orbitals of a valance shell of an atom combine to form 3 new equivalent orbitals (same energy and shape).
  • Sp2 hybrid orbitals have one third s character and two third of p character.
  • 120º is the bond angle between two sp2 hybrid orbitals.

E.g.: –

1) BCl3 (Boron Trichloride Molecules):

sp2 Lewis structure of boron trichloride

The three sp2 hybrid orbitals of chlorine overlapping with half-filled p orbital of each chlorine.

2) C2H4 (Ethylene)

  • Two carbons in Ethylene are in sp2 hybrid state.
  • One sp2 hybrid carbon orbital overlaps with another sp2 hybrid orbital of carbon forming C-C sigma bond remaining sp2 hybrid orbitals of carbon forms C-H sigma bond by overlapping with 1s orbital of hydrogen.
  • The unhybridized two 2Pz orbitals of each carbon atom overlap sidewise forming pi bond between two carbon atoms
Lewis structure of ethylene

How to draw Lewis structure for SP2?

Here we will learn how to draw Lewis structure for sp2 hybridization

  • settle the entire number of valance electrons of the molecule.

1) Select the central bonding atom.

Rules for selecting central atom

  1. Choose the least number of atoms as central atom.

                                     [or]

  • Least electro negative atom as central atom.

                                     [or]

  •  Largest sized atom as central atom.

                                     [or]

  • Atom with highest atomic number.

Note: –

  • Central atom may have 8 or more electrons in its valance shell.
  • Hydrogen and Fluorine atom does not act as central atom.
  1. 2) The remaining other atoms are arranged around the central atoms.
  2. 3) The central atom and the surroundings atoms are bonded using sigma bond.
  3. 4) Electrons are redistributed between the central atom and surrounding atoms to complete its octet.

E.g.: –   C2H4 (Ethylene)

Lewis structure of ethylene
  • Central atom is Carbon atom
  • Total number of valance electrons is 12 electrons.
  • 4 hydrogen atoms arranged around the carbon atom and bonded by sigma bond.
  • Distribute the electrons so that the carbon atoms attain its octet.
  • Hydrogen needs 2 electrons to attain octet. 

SP2 Lewis structure shape

There are two possible shapes for sp2 hybridized molecules

The two possible shapes for sp2 hybridized molecules are;

  1. 1) Trigonal panel (AB3).
  2. 2) Bent (AB2L).

A – Central atom

B – Atoms surroundings central atom

L – Lone pair of electrons

E.g.: – 1) Trigonal panel: BF3, AlCl3, SO3, NO3 etc.

triangular planar shape of BF3

2) Bent: SO2, PbCl2, SnCl2 etc.

Bent shape of so2

SP2 Lewis structure formal charges

Atoms forms covalent bond by giving or loosing valance electrons. A formal charge is assigned to some atoms in the Lewis structure of certain compounds. It can be calculated using the formula

Formal charge of an atom in a Lewis structure = Total number of valance electrons in the free atom – Total number of lone pair of electrons – Half the total number of bonding electrons.

E.g.: – Ozone (O3)

Here central oxygen atom (O1) is sp2 hybridized

The total number of valance electrons in O1 = 6

The total number of lone pair electrons in O1 = 2

Total number of bonding electrons in O1= 6

\ Its formal charge = 6 – 2 – ½ (6)

                                   = +1

SP2 Lewis structure lone pairs

Sp2 hybridized compound have one nonbonding pair of electrons in the Lewis structure. They are in the form AB2L. There are two bond pair of electrons and one lone pair of electrons.

E.g.: – SO2, PbCl2, SnCl2 etc.

Here in SO2 central atom is S and has one lone pair of electrons and two bond pairs bonded to 2 oxygen atoms.

  • These sp2 hybridized molecules with lone pairs are bent shaped.
  • Its bond angle is reduced from 120º to 119º because of the presents of lone pair of electrons.

SP2 Lewis structure resonance

In order to explain all the properties of a molecule, the molecule exist as a hybrid structure. This phenomenon is known as resonance.

E.g.: – C6H6 (Benzene – sp2 hybridized)

Resonance structure of benzene
  • The structure I & II are called resonating hybrids/ contributing structures/ canonical forms.
  • The actual structure of the molecule is a resonance hybrid thus the benzene molecule has 12 σ bonds and 3 π bonds hence the benzene molecule has total 15 covalent bonds.

SP2 polar or nonpolar

A covalent bond is formed when the bonding atoms share equal electrons. Let A & B be two atoms taking part in bond formation.

Polar covalent bond

If the atom A is more electronegative than the atom B and vice versa then when the bond forms the bonding pair of electrons tends to displace towards the more electronegative atom. Then the much negatively charged atom tends to have a partial negative charge and the not so much as electronegative atom tends to have partial positive charge. Such bonds are called polar covalent bond.

E.g.: – Formaldehyde (H2CO)

Here in formaldehyde, in the bond C = O oxygen is more electronegative than the carbon atom and therefor the bonding electrons are more attracted towards the oxygen atom resulting in the cause of oxygen to have a partial negative charge and carbon to have partial positive charge and thus making the bond polar.

Non polar covalent bond

If both the atoms A & B are equally electronegative, then the bonding pair of electrons will be equally attracted by the two atoms. Such bonds are called non-polar covalent bonds.   

E.g.: – BF3 (Boron Trifluoride)

Because of the high symmetric structure of BF3 that is the trigonal planet shape. The dipole moments of three BF bonds had been nullified out leading the aftermath dipole moment come to to zero. Thus, making it a non-polar compound.

SP2 uses

  • Carbon atom makes grate use of sp2 hybridization to form compounds like Ethene (C2H4), Formaldehyde (H2CO), Acetic acid (CH3COOH), Benzene (C6H6) etc.
  • Sp2 hybridization helps in understanding the molecular properties of compounds like SO2, C2H4, BF3, AlCl3 etc.
  • Sp2 hybridization plays a great role in explaining the stability and structure of Benzene.

   

Lina Karankal

Hi..I am Lina Karankal, I have completed my Master's in Chemistry. I always like to explore new areas in the field of Chemistry. Apart from this, I like to read, travel and listen to Music.

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