CHF3 Lewis dot structure, molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, polar or nonpolar
CHF3 is the chemical formula for trifluoromethane, also known as fluoroform or carbon trifluoride. It is a colorless, odorless, non-flammable gas. Its major use is in the semiconductor industry for plasma etching silicon compounds.
In this article, we have discussed CHF3 chemistry, including how to draw its Lewis dot structure, what is its molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, polarity, etc.
So to learn all this valuable information, continue reading!
The Lewis structure of CHF3 consists of a carbon (C) atom at the centre, which is bonded to one hydrogen (H) atom and three atoms of fluorine (F). There are a total of 4 electron density regions around the central C-atom in the CHF3 Lewis structure.
All 4 electron density regions are comprised of bond pairs; thus, there is no lone pair of electrons on the central C-atom in CHF3.
Below is a step-by-step guide that you can follow to draw the Lewis dot structure of CHF3.
As three different elemental atoms are present in CHF3, so you first need to look for the position of these elements in the Periodic Table.
Carbon (C) belongs to Group IV A (or 14), so it has a total of 4 valence electrons. Fluorine (F) is present in Group VII A (or 17); hence it has 7 valence electrons, while hydrogen (H) lies at the top of the Periodic Table containing a single valence electron only.
∴ The CHF3 molecule consists of 1 C-atom, 3 F-atoms, and 1 H-atom. Therefore, the total valence electrons available for drawing the Lewis dot structure of CHF3 = 1(4) + 3(7) + 1(1) = 26 valence electrons.
2. Choose the central atom
In this second step, usually the least electronegative atom out of all the concerned atoms is chosen as the central atom.
This is because the least electronegative atom is the one that is most likely to share its electrons with the atoms spread around it.
Fluorine is the most electronegative element in the Periodic Table. It is more electronegative than both carbon and hydrogen, so an F-atom cannot be selected as the central atom in the CHF3.
Hydrogen (E.N = 2.20) is less electronegative than carbon (E.N = 2.55). Still, it cannot be chosen as the central atom because a hydrogen (H) atom can accommodate only 2 electrons so that it can form a bond with a single adjacent atom only. This denotes that H is always placed as an outer atom in a Lewis structure.
As a result, the carbon (C) atom is chosen as the central atom in the Lewis dot structure of trifluoromethane (CHF3), while three F and one H atoms are placed around it as outer atoms, as shown in the figure below.
3. Connect outer atoms with the central atom
Now we need to connect the outer atoms with the central atom of the Lewis structure using single straight lines.
As one hydrogen and three fluorine atoms are the outer atoms in the trifluoromethane, so these atoms are joined to the central C-atom using straight lines.
Each straight line represents a single covalent bond, i.e., a bond pair containing 2 electrons. There are a total of 4 single bonds in the above diagram.
As 4(2) = 8, that means 8 valence electrons are already consumed out of the 26 initially available.
4. Complete the duplet and/or octet of the outer atoms
As we already identified, the hydrogen and fluorine atoms are the outer atoms in the Lewis dot structure of CHF3.
Each hydrogen (H) atom requires a total of 2 valence electrons in order to achieve a stable duplet electronic configuration.
A C-H single bond already represents 2 valence electrons around each H-atom. This means the H-atom already has a complete duplet in the Lewis structure drawn till yet. Thus, we do not need to make any changes with regard to the hydrogen atom in this structure.
In contrast, an F-atom needs a total of 8 valence electrons to achieve a stable octet electronic configuration. A C-F bond represents 2 electrons which denotes that each outer F atom needs 6 more electrons to complete its octet. Consequently, 6 valence electrons are placed as 3 lone pairs on all three fluorine (F) atoms in the CHF3 Lewis structure, as shown below.
5. Complete the octet of the central atom
In the Lewis structure drawn till step 4, the central carbon (C) atom has four single bonds around it, i.e., 3 C-F single bonds and 1 C-H single bond. Four single covalent bonds represent a total of 4(2) = 8 valence electrons. In short, the central C-atom already has a complete octet electronic configuration.
Total valence electrons used till step 4 = 4 single bonds + 3 (electrons placed around each F-atom, shown as dots) = 4(2) + 3(6) = 26 valence electrons.
Total valence electrons available – electrons used till step 4 = 26 – 26 = 0 valence electrons.
All the valence electrons initially available are now used up; therefore, there is no lone pair of electrons on the central C-atom in the Lewis dot structure of CHF3.
The final step is to check the stability of the Lewis structure obtained in this step. Let us do that using the formal charge concept.
6. Check the stability of Lewis’s structure using the formal charge concept
The fewer formal charges present 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.
The absence of any formal charges on the bonded atoms in the CHF3 Lewis structure marks the incredible stability of this structure.
Now that we have obtained the correct and best Lewis representation of trifluoromethane (CHF3), let us move ahead and discuss its shape, geometry, and other interesting chemistry facts.
What are the electron and molecular geometry of CHF3?
The CHF3 molecule has an identical electron geometry and molecular geometry or shape, i.e., tetrahedral. There are a total of 4 electron density regions around the central C-atom in CHF3, and there is no lone pair of electrons on this central atom.
Thus, there is no distortion witnessed in the shape and geometry of the molecule.
Molecular geometry of CHF3
The molecular geometry or shape of CHF3 is tetrahedral. The absence of any lone pair of electrons on the central C-atom in CHF3 means there are no lone pair-lone pair and lone pair-bond pair electronic repulsions present in the molecule.
A bond pair-bond pair repulsive effect exists, which makes the bonded electron pairs occupy the four corners of a tetrahedron, as shown in the figure below.
Electron geometry of CHF3
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, the ideal electron geometry of a molecule containing a total of 4 electron density regions around the central atom is tetrahedral.
In CHF3, there are 4 single bonds around the central carbon atom which makes a total of 4 electron density regions. Thus, its electron geometry is also tetrahedral.
A shortcut to finding the electron and the molecular geometry of a molecule is by using the AXN method.
AXN is a simple formula to represent the number of atoms bonded to the central atom in a molecule and the number of lone pairs present on it.
It is used to predict the shape and geometry of a molecule based on the VSEPR concept.
AXN notation for CHF3 molecule
A in the AXN formula represents the central atom. In the CHF3 molecule, a carbon (C) atom is present at the center so A = C.
X denotes the atoms bonded to the central atom. In CHF3, one hydrogen (H) and three fluorine (F) atoms are bonded to the central carbon so X = 1 + 3 = 4.
N stands for the lone pairs present on the central atom. As per the Lewis structure of CHF3, there are no lone pairs of electrons on the central carbon so N = 0.
As a result, the AXN generic formula for CHF3 is AX4.
Now, you may have a look at the VSEPR chart below.
The VSEPR chart confirms that the molecular geometry or shape of a molecule with an AX4 generic formula is identical to its electron pair geometry, i.e., tetrahedral, as we already noted for trifluoromethane (CHF3).
Hybridization of CHF3
The central carbon (C) atom in the trifluoromethane (CHF3) molecule is sp3 hybridized.
The electronic configuration of carbon is 1s22s22p2.
During chemical bonding, the 2s electrons of carbon get unpaired. One of the two electrons shifts to the empty 2p atomic orbital.
The 2s orbital and three half-filled 2p atomic orbitals of carbon consequently hybridize to yield four sp3 hybrid orbitals. Each sp3 hybrid orbital is equivalent and contains a single electron only. It possesses a 25% s character and a 75% p-character.
Three of the four sp3 hybrid orbitals of carbon form C-F sigma (σ) bonds by overlapping with the p-orbitals of the fluorine atoms. The remaining sp3 hybrid orbital of carbon forms the C-H sigma (σ) bond by overlapping with the s-orbital of the fluorine atom in CHF3.
Refer to the figure drawn below.
Another shortcut to finding the hybridization present in a molecule is by using its steric number against the table given below. The steric number of central C-atom in CHF3 is 4, so it has sp3 hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The CHF3 bond angle
The bonded atoms in a CHF3 molecule possess a mutual bond angle of 109.5°, as expected in a symmetrical tetrahedral shape. The C-F bond length is 134 pm, while each C-H bond length is 109 pm in CHF3.
The C-X bond length is greater than a C-H bond length in halo alkanes, where X is a halogen. This is because of the greater electronegativity of the halogen atom that attracts the shared C-X electron cloud towards itself to a greater extent.
According to Pauling’s electronegativity scale, a covalent bond is considered polar if the concerned atoms have an electronegativity difference greater than 0.5 units.
An electronegativity difference of 0.35 units exists between a carbon (E.N = 2.55) and a hydrogen (E.N = 2.20) atom. Therefore, the C-H bond is only weakly polar.
In contrast to that, fluorine is highly electronegative. An electronegativity difference of 1.43 units exists between the carbon and fluorine (E.N = 3.98) atoms.
Hence each C-F bond is extremely polar in the CHF3 molecule, and each possesses a specific dipole moment value (symbol µ). Each F-atom obtains a partial negative (δ–) charge while the central C-atom attains a partial positive (δ+) charge.
The highly electronegative halogen atoms not only attract the shared electron cloud of each C-F bond but also attracts C-H electrons. Therefore, the electron cloud stays non-uniformly distributed over the molecule overall. In conclusion, CHF3 is a polar molecule (net µ = 1.8 D).
The CHF3 Lewis structure displays a total of 26 valence electrons, i.e., 26/2 = 13 electron
Out of the 13 electron pairs, there are 4 bond pairs and 9 lone pairs of electrons.
The 4 bond pairs comprise 3 C-F bonds and 1 C-H single covalent bond.
Each F-atom contains 3 lone pairs each, while there is no lone pair of electrons on either the central C-atom or the H-atom in the CHF3 Lewis structure.
What is the molecular geometry of CHF3 as per the VSEPR concept?
As per the VSEPR concept, the AXN generic formula for CHF3 is AX4E0 orAX4. One C-atom at the center, one H-atom, and 3 F-atoms are attached.
There is no lone pair of electrons on the central C-atom; thus, the molecule adopts a symmetrical tetrahedral shape or molecular geometry.
How is the shape of CHF3 different from its ideal electronic geometry?
CHF3 has an identical shape to its ideal electron pair geometry i.e., tetrahedral. The absence of any lone pair of electrons on the central C-atom denotes there are no lone pair-lone pair or lone pair-bond pair electronic repulsions present in the molecule.
Thus, no distortion is witnessed in its shape and/or geometry.
How is the shape of CHF3 different from that of CH3Cl?
Trifluoromethane (CHF3) and chloromethane (CH3Cl) have a similar shape, i.e., tetrahedral. Four atoms are directly bonded to the central C-atom, and it has no lone pair of electrons present on it.
In CHF3, there is one C-H bond and three C-F bonds, while in CH3Cl, there are three C-H bonds and one C-Cl bond.
Which has the maximum bond angle and bond length; CHF3, CHCl3, CHBr3, or CHI3?
All the above molecules have a symmetrical tetrahedral shape, thus an ideal bond angle of 109.5°. However, the electronegativity of the halogens bonded to the central C-atom increases in the order I < Br < Cl < F, so the strength of the C-X (where X = halogen) bond decreases.
The more electronegative X-atom more strongly attracts the C-X shared electron cloud. Consequently, the C-X bond length increases.
The total number of valence electrons available for drawing trifluoromethane or fluoroform (CHF3) Lewis structure is 26.
CHF3 has an identical electron and molecular geometry or shape i.e., tetrahedral.
The central C-atom has sp3 hybridization in the CHF3 molecule.
The bonded atoms form a mutual bond angle of 109.5° in the tetrahedral CHF3 molecule.
The C-H bond is stronger and has a bond length of 109 pm, while each C-F bond length is 134 pm in CHF3.
The CHF3 molecule is overall polar (net µ = 1.8 D) due to the high electronegativity of the fluorine atoms, which attracts the C-H electron cloud in addition to attracting the C-F bonded electrons.
Zero formal charges present on all the bonded atoms in the CHF3 molecule account for the extraordinary stability of the Lewis structure drawn in this article.
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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