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

This article explains sp hybridization, how to draw the sp lewis structure for an sp hybridized molecule, and other details mentioned in the title.

Atomic orbitals overlap to form new orbitals which differ in energies, shapes, and strengths. This process is called hybridization. In sp hybridization, one s orbital combines with a p orbital(px,py,pz). This is also known as linear hybridization.

  • Each sp hybrid orbital is stronger than the pure s or pure p orbital
  • The number of atomic orbitals which participate in hybridization produces the same number of hybrid orbitals.
sp mixing
Mixing of s and p orbital to form sp hybrid orbitals
  • In the case of an sp hybridized molecule like Be , the electronic configuration of Be in the ground state is [He]2s2 It undergoes excitation by promoting an electron from 2s to 2p and gets the configuration [He]2s1 2p1 .
  • The 2s and 2p orbitals of Be combine to form two equivalent sp hybridized orbitals.
  • These hybrid orbitals form a sigma bond with the two 3p orbitals of Cl.
Becl2 ls 1
sp hybridization in BeCl2

Octet Rule

Atoms try to achieve the octet electronic configuration by either sharing valence electrons(covalent bonding) or transferring valence electrons, either by losing or gaining(ionic bonding).

  • Before learning how to draw the lewis structure for any molecule, we need to know the octet rule.
  • In 1916 Kössel and Lewis developed a very important theory known as the electronic theory of chemical bonding.
  • According to this theory, atoms tend to attain eight electrons(octet) in their outermost shell to gain stability like a noble gas. This is known as the octet rule.
  • There are some exceptions to this rule(hydrogen, helium, lithium, etc.)
  • In some cases, the valence electrons in the central atom can be beyond eight, too, as found in PF5 and SF6, where P has ten valence electrons, and S has 12 valence electrons. These are exceptions to the octet rule.

How to draw the lewis structure for sp hybridized molecule

Lewis structure is a diagram that shows how the lone pairs and bond pair electrons are distributed in a molecule.

  • Lewis’s structure uses the octet rule. We represent electrons by dots and bonds by a dash.
  • The lewis structure does not represent the actual shape of the molecule but helps understand the formation of the molecules.
  • We draw Lewis structures keeping some rules and guidelines in mind.
  • First, we will each atom’s valence electrons in a molecule. For example, in the case of BeCl2 ( an sp hybridized molecule), the total number of valence electrons is 2 + (7 X 2) =16 (two of Be and seven of each chlorine atom).
  • Then we identify the central atom of the molecule. This is usually the atom that is either least in number or least electronegative. 
  • In BeCl2 , Be is the central atom.
  • Another way of identifying the central atom is that it might be the only one that can form more than one bond. 
  • The valence electrons have to be arranged so that every atom shares a pair of electrons and forms a bond.
  • Then arrange the rest of the electron pairs to form lone pairs or multiple bonds until each atom completes its octet.
  • In the case of anions, we add electrons according to the negative charge present on them. If an anion has a -1 charge, we will add an electron.
  • Similarly, in the  case of cations, we will subtract electrons depending on the charge of the cation.
  • The lewis structure of BeCl2  is shown below.
sp lewis structure
sp lewis structure of BeCl2
  • Be does not complete its octet in BeCl2  as Be does not follow the octet rule. It is an exception.

Sp Lewis structure shape

To predict the shape of the molecule, we use the VSEPR theory.

The shape of a molecule cannot be predicted using the lewis structure( it only tells us about the arrangement of electrons).

In BeCl2 , Be has two valence electrons used to form bonds with the two chlorine atoms.

Be has no lone pair, and the two bond pairs align 180 degrees to each other, forming a linear shape.

Formal charge

Since different atoms have different electronegativities, electrons in a chemical bond are not shared equally.

  • If we forget about the electronegativities and assume that the electrons in a bond are equally shared, then the charge assigned to an atom in a molecule would be the formal charge.
  • If we calculate the number of valence electrons in a free atom(not bonded to any other atom or isolated atom) and then calculate the number of valence electrons to that atom in a molecule, the difference will give us the formal charge on that atom.
  • It is a hypothetical charge and does not represent the electron density distribution.
  • The formal charge of an atom in a molecule= V-1/2[B] -N
  • Here V is the total number of valence electrons on free atoms, B is the total number of shared electrons, and N is the total number of non-bonded unshared electrons.
  • Be has two valence electrons in the isolated state, the total number of shared electrons is four(two bond pairs), and the number of unshared electrons/lone pair is zero.
  • Using the above information, the formal charge of Be in BeCl2  is 2-1/2[4]-0= 0.
  • Cl has seven valence electrons in the isolated state, the total number of shared electrons is four(two bond pairs), and it has six unshared electrons.
  • Using the above information, the formal charge of each chlorine atom in BeCl2

 is 7-1/2[2]-6=zero.

Sp lewis structure resonance

We can draw multiple lewis structures for a molecule that has lone pairs or can form multiple bonds.

These are called resonance structures of lewis formulae.

The formal charge helps predict the most stable lewis structure in case of resonance where more than one lewis structure is possible.

Lewis structures with low formal charge are the most stable.

We will draw different lewis structures of CO2  and determine the most stable structure using formal charge.

lewis structure resonance of CO2

Sp polar or non-polar

Polarity and non-polarity depend on the electronegativity difference between the atoms and the net dipole moment of a molecule.

Polarity and non-polarity depend on the electronegativity difference between the atoms and the net dipole moment of a molecule.

When the bonded atoms have the same electronegativity, they share electrons equally, and the molecule will be non-polar.

Sometimes, polar bonds in a molecule can have symmetrical geometry such that they cancel each other’s dipole moment. This results in making the molecule non-polar.

When the bonded electrons are not shared equally due to electronegativity difference, the electron density is greater on the more electronegative atom. As a result, there will be a slightly positive centre and a slightly negative centre in the molecule(a dipole will be formed).

Sp hybrid molecules have a linear structure. If the same atoms are present around the central atom in an sp hybridized molecule, the compound is non-polar even if individual bonds are polar.

This is because the net dipole moment is zero in the above case.

Therefore, BeCl2  is non-polar despite having an electronegativity difference between Be and Cl(individual Be-Cl bonds are polar, but the Be  molecule is non-polar due to the net dipole moment being zero).

Uses of sp lewis structure

To understand chemical bonding, we need to identify lone pair and bond pair electrons in a molecule.

  • Lewis structure helps visualize the arrangement of valence shell electrons in a molecule.
  • It helps in understanding chemical bonding.

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