SnCl2 Lewis structure, molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, polar vs nonpolar
SnCl2 represents the chemical formula for tin (II) chloride, commonly known as stannous chloride. It is a white crystalline solid, highly soluble in water, greatly valued for its role as a reducing agent.
SnCl2 is used in the electroplating industry, dyeing and textile, as well as in photography.
This article is important if you want to learn to draw the Lewis dot structure of SnCl2, its molecular geometry or shape, electron geometry, bond angles, hybridization, formal charges, polarity, etc.
The Lewis structure of stannous chloride (SnCl2) comprises a tin (Sn) atom at the center. The central Sn-atom is single-covalently bonded to two chlorine (Cl) atoms, one on either side of the molecule. There is a lone pair of electrons on the central Sn-atom in SnCl2. Also, both the terminal Cl-atoms carry 3 lone pairs, respectively.
Drawing the Lewis dot structure of SnCl2 is super easy. So, come along and draw it with us by following the simple steps given below.
Steps for drawing the Lewis dot structure of SnCl2
1. Count the total valence electrons present in SnCl2
The two distinct elements present in SnCl2 are tin and chlorine.
Tin (Sn) is present in Group IV A (or 14) of the Periodic Table, having a total of 4 valence electrons in each atom.
In contrast, chlorine (Cl) is a halogen located in Group VII A (or 17), implying that it has 7 valence electrons in each atom.
Total number of valence electrons in tin = 4
Total number of valence electrons in chlorine = 7
The SnCl2 molecule comprises 1 Sn-atom and 2 Cl-atoms.
∴ Therefore, the total valence electrons available for drawing the Lewis dot structure of SnCl2 = 1(4) + 2(7) = 18 valence electrons.
2. Find the least electronegative atom and place it at the center
By convention, the least electronegative atom out of all those available is chosen as the central atom while drawing the Lewis structure of a molecule.
The least electronegative atom can easily form covalent bonds with other atoms by sharing its electrons.
Tin (E.N =1.96) is undoubtedly less electronegative than chlorine (E.N = 3.16).
Therefore, the Sn-atom is placed as the central atom in the SnCl2 Lewis structure, while both the Cl-atoms occupy outer positions, as shown below.
3. Connect the outer atoms with the central atom
In this step, the outer atoms, i.e., 2 Cl-atoms, are joined to the central Sn-atom using single straight lines.
A straight line represents a single covalent bond, i.e., a bond pair containing 2 electrons.
In the above structure, there are 2 single bonds, i.e., 2(2) = 4 valence electrons are already consumed out of the 18 initially available.
Now let’s see in the next steps where to place the rest of the 14 valence electrons in the SnCl2 Lewis dot structure.
4. Complete the octet of the outer atoms
A Cl-atom needs a total of 8 valence electrons in order to achieve a stable octet electronic configuration.
An Sn-Cl bond represents 2 valence electrons already present around each chlorine atom in the Lewis structure drawn so far.
Therefore, the remaining 6 valence electrons are placed as 3 lone pairs around each Cl-atom to complete its octet.
5. Check if the central atom has a complete octet or not
Total valence electrons used till step 4 = 2 single bonds + 2(electrons placed around each Cl-atom, shown as dots) = 2(2) + 2(6) = 16 valence electrons.
Total valence electrons – electrons used till step 4 = 18 – 16 = 2 valence electrons.
Thus, these 2 valence electrons are placed as a lone pair on the central Sn-atom in the SnCl2 Lewis structure, as shown below.
However, you may note that the central tin atom still has an incomplete octet in the above Lewis structure.
It has 2 single bonds + 1 lone pair = 2(2) + 2 = 6 valence electrons surrounding it only, instead of a complete octet electronic configuration having 8 valence electrons.
But the subject called chemistry always surprises us with exceptions to rules and patterns.
Accordingly, the tin atom is an exception.
Elements in the lower periods of the periodic table, such as tin from Group 14, can form stable compounds even with an incomplete octet.
The incomplete octet of tin is another factor for SnCl2 being a good Lewis acid; it can readily accept another lone pair, forming complexes with electron-rich ligands.
As a final step, we just need to check the stability of the SnCl2 Lewis structure obtained above. We can do so by applying the formal charge concept.
6. Check the stability of Lewis’s structure using the formal charge concept
The less the formal charge on the atoms of a molecule, the better the stability of its Lewis structure.
The formal charges can be calculated using the formula given below.
Formal charge = [valence electrons- nonbonding electrons- ½ (bonding electrons)].
Now let us use this formula and the Lewis structure obtained in step 5 to determine the formal charges present on the SnCl2-bonded atoms.
What are the electron and molecular geometry of SnCl2?
The molecular geometry or shape of SnCl2 w.r.t the central Sn-atom is bent, angular or V-shaped. However, its ideal electron geometry is trigonal planar. The presence of a lone pair of electrons on the central Sn-atom distorts the overall molecular shape.
Molecular geometry of SnCl2
The molecular geometry or shape of stannous chloride (SnCl2) w.r.t the central Sn-atom is bent, angular or V-shaped.
The presence of a lone pair of electrons on the central Sn-atom leads to strong lone pair-bond pair electronic repulsions. This strong repulsive effect distorts the overall molecular geometry of SnCl2.
To minimize this repulsion, the bonded Cl-atoms tilt away from the lone pair at the center to form a bent or V-shaped molecule, as shown below.
Electron geometry of SnCl2
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, the ideal electron geometry of a molecule containing a total of 3 electron density regions around the central atom is trigonal planar.
In SnCl2, the Sn-atom at the center is surrounded by 2 bond pairs, and it has 1 lone pair of electrons, making a total of 3 electron density regions.
Hence, the ideal electron pair geometry of the SnCl2 molecule is trigonal planar.
An easy trick to finding a molecule’s electron and molecular geometry is using the AXN method.
AXN is a simple formula representing the number of bonded atoms and lone pairs present on the central atom.
It is used to predict the shape and geometry of a molecule using the VSEPR concept.
AXN notation for SnCl2
A in the AXN formula represents the central atom. In the SnCl2 molecule, a tin (Sn) atom is present at the center, so A = Sn.
X denotes the atoms bonded to the central atom. In SnCl2, 2 Cl-atoms are directly bonded to the central Sn-atom. So X = 2 for SnCl2.
N stands for the lone pairs present on the central atom. As per the Lewis structure of SnCl2, the central Sn-atom has 1 lone pair of electrons. Thus, N = 1 for SnCl2.
As a result, the AXN generic formula for SnCl2 is AX2N1.
Now, you may have a look at the VSEPR chart below.
The VSEPR chart confirms that a molecule with AX2N1 generic formula possesses an identical electron and molecular geometry or shape, i.e., bent, angular or V-shaped, as we already noted down for the stannous chloride (SnCl2) molecule.
Hybridization of SnCl2
The central Sn-atom is sp2 hybridized in SnCl2.
The electronic configuration of tin (Sn) is [Kr] 4d10 5s2 5p2.
During chemical bonding in SnCl2, the 5s atomic orbital of tin hybridizes with its two half-filled 5p atomic orbitals to produce three sp2 hybrid orbitals.
Each sp2 hybrid orbital possesses a 33.3 % s-character and a 66.7 % p-character. However, these three sp2 hybrid orbitals of tin are not equivalent.
One of these possesses paired electrons which are situated as a lone pair on the central Sn-atom in SnCl2.
The other two sp2 hybrid orbitals containing unpaired electrons form Sn-Cl sigma bonds by sp2-p orbital overlap with adjacent Cl-atoms, as shown below.
Another shortcut to finding the hybridization present in a molecule is using its steric number against the table given below.
The steric number of the Sn-atom in SnCl2 is 3, so it has sp2 hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The bond angles of SnCl2
The ideal bond angle in a trigonal planar molecular shape is 120°.
However, it is due to the distortion present in the molecular shape of SnCl2 that the Cl-Sn-Cl bond angle decreases from the ideal value to approx. 95°.
Conversely, each Sn-Cl bond length is equal to 242 pm in the SnCl2 molecule.
As per Pauling’s electronegativity scale, a polar covalent bond is formed between two dissimilar atoms having an electronegativity difference between 0.4 to 1.6 units.
In SnCl2, a high electronegativity difference of 1.20 units is present between the covalently bonded tin (E.N = 1.96) and chlorine (E.N = 3.16) atoms in each Sn-Cl bond.
Thus, both the Sn-Cl bonds are individually polar in the SnCl2 molecule.
Chlorine, being more electronegative, strongly attracts the Sn-Cl electron cloud from both ends, largely towards itself.
The Cl-atoms thus gain a partial negative charge (δ–), while the central Sn-atom obtains a partial positive charge (δ+) in SnCl2.
The strong Sn-Cl dipole moments stay uncancelled in the asymmetric bent, angular, or V-shape of stannous chloride. Hence, SnCl2 is overall strongly polar (net µ > 0).
How can you determine the Lewis dot structure of SnCl2?
The Lewis dot structure of stannous chloride (SnCl2) displays a total of 18 valenceelectrons i.e., 18/2 = 9 electron pairs.
Out of the 9 electron pairs, there are 2 bond pairs and 7 lone pairs of electrons.
A tin (Sn) atom at the center is single-covalently bonded to two chlorine (Cl) atoms, one on either side in the SnCl2 Lewis structure.
There is 1 lone pair of electrons on the central Sn-atom while each Cl-atom carries 3 lone pairs, respectively.
How many bond pairs and lone pairs surround the tin atom in the SnCl2 Lewis structure?
The central Sn-atom is surrounded by 2 (Sn-Cl) bond pairs and 1 lone pair in the SnCl2 Lewis structure.
How can the VSEPR theory be applied to explain the shape of SnCl2?
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, SnCl2 is an AX2N1-type molecule.
To an Sn-atom at the center, 2 Cl-atoms are attached. The central Sn-atom also has a lone pair of electrons. Thus, the molecular shape of SnCl2, according to the VSEPR theory, is bent, angular or V-shaped.
Why is the molecular shape of SnCl2 different from its electron geometry?
A lone pair of electrons on the central Sn-atom in SnCl2 leads to a strong lone pair-bond pair repulsive effect. To minimize the electronic repulsions, the bonded Cl-atoms tilt away from the center.
The stannous chloride (SnCl2) molecule thus occupies a bent, angular or V-shape, different from its ideal electronic geometry, i.e., trigonal planar.
Is the structure of SnCl2 angular? If yes, justify it.
Yes. The lone pair of electrons present on the central Sn-atom in SnCl2 leads to electronic repulsions, which in turn make the stannous chloride molecule occupy an angular shape and geometry.
The Cl-Sn-Cl bond angle reduces from an ideal value of 120° to about 95°.
What are the shapes of CH4, SnCl2, NH3, PCl5 and SF6?
The molecular shape of methane (CH4) is tetrahedral. To a C-atom at the center, four H-atoms are single covalently bonded like four corners of a tetrahedron.
The shape of stannous chloride (SnCl2) is bent, angular or V-shaped, as the central Sn-atom has 1 lone pair of electrons.
Ammonia (NH3) is a trigonal pyramidal molecule. To an N-atom at the center, three H-atoms are attached, forming a triangular base, while the lone pair on nitrogen forms a pyramid at the top.
The shape of phosphorus pentachloride (PCl5) is trigonal bipyramidal. 3 Cl-atoms attached to the central P-atom forms a triangular base, while the other 2 Cl-atoms form two pyramids, one above and the other below the molecule.
Sulfur hexachloride (SCl6) is an octahedral molecule. The central S-atom is directly bonded to 6 Cl-atoms. However, there is no lone pair of electrons on the central S-atom to distort the overall molecular shape of SCl6.
The total number of valence electrons available for drawing the tin (II) chloride (SnCl2) Lewis structure is 18.
The molecular geometry or shape of SnCl2 is bent, angular, or V-shaped.
The ideal electronic geometry of SnCl2 is trigonal planar.
The central Sn-atom is sp2 hybridized in SnCl2.
The Cl-Sn-Cl bond angle is equal to 95° while each Sn-Cl bond length equals 242 pm in SnCl2.
SnCl2 is a polar molecule (net µ > 0) as the Sn-Cl dipole moments do not get canceled equally in the asymmetric bent shape of stannous chloride.
Zero or no formal charges on the covalently bonded atoms in SnCl2 ensure the extraordinary stability of the Lewis structure drawn in this article, even though the central Sn-atom has an incomplete octet.
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
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