Selenium tetrachloride is the inorganic compound of the composition with the formula SeCl4 . This compound exists as a yellow to white volatile solid. It is one of two commonly available selenium chloride , the other example being selenium monochloride , C 2 chlorine 2 . SeCl 4 is used in the synthesis of other selenium compounds. The electron dot structure gives an idea about the planar (2D) structure of a molecule. This article will discuss about the Lewis structure of SeCl4 and the method to draw it, To draw SeCl4 Lewis structure, atomic symbols of atoms are written, electrons in outermost orbitals of atoms are shown by dot symbols. From this we can infer many properties like hybridization, size, polarity etc.
Lewis Structure for SECL4
The SeCl4 Lewis structure gives the idea about the electrons in the outermost orbitals of the atoms. These electrons are responsible for specific properties in the molecule . To draw the SeCl4 Lewis structure, the atomic symbols of the atoms are written, which is ‘Se’ for selenium and ‘Cl’ for chlorine. The outermost orbital electrons of an atom are shown by dot symbols around that particular atom of the selenium tetrachloride molecule, selenium is a ‘group 16’ element and chlorine is a ‘group 17 element in the periodic table, electronic configuration of selenium: [Ar] 3d10 4s2 4p4. Electronic configuration of chlorine: [Ne] 3s2 3p5. So the outermost orbital electrons of the selenium atom are six and those of the chlorine atom are seven . For four chlorine atoms and one selenium atom , the total number of electrons in the outermost orbitals is {6 + (7×4)} = 34. Hence 17 pairs of electrons participate to form a SeCl4 molecule.
The less electronegative atom in the selenium molecule is the central atom. Chlorine atoms surround the central atom. Four chlorine atoms form sigma bonds (single bond) with selenium atom, eight electrons (four pairs of electrons) take part in bond formation. Each chlorine atom in the SeCl4 molecule has six unshared electrons. The central atom of selenium has a pair of shared electrons. Straight lines are used to show the bonding electrons of a sigma bond in a molecule.
reactions
Selenium tetrachloride can be reduced in situ by the use of dichloride triphenylstibin :
SeCl 4 + SbPh 3 → Clx 2 + Cl 2 SbPh 3
Selenium reacts with water to give tetrachloride hard and hydrochloric acid :
SeCl 4 + 3 H 2 O → H 2 Seo 3 + 4 HCl
Upon treatment with selenium dioxide , it gives selenium oxychloride :
SeCl 4 + Se 2 → 2SeOCl 2
Synthesis and Structure
The compound is prepared by treating selenium with chlorine . [3] When the reaction selenium is heated, the product sublimes from the reaction flask. The volatility of selenium tetrachloride can be exploited for the purification of selenium.
The solid SeCl 4 is actually a tetrameric cuboidal -type cluster for which the Si atom of a Se 6 octahedron sits at the four corners of the cube and the bridging Cl atoms sit at the other four corners. The bridging Se–Cl distance is greater than the terminal Se–Cl distance, but all Cl–Se–Cl angles are approximately 90°. [4]
SeCl4 has often been used as an example for teaching the rules of VSEPR hypervalent molecules . As such, one would predict four bonds but five electron groups would give rise to one sees geometry . This is clearly not the case with the crystal structure . Others have suggested that the crystal structure can be represented as Cl 3 + and Cl − . This formulation would predict the pyramidal geometry for SeCl 3 +cation with a Cl–Se–Cl bond angle of about 109°. However, this molecule is a classic example of a situation where the maximum molecular formula cannot be achieved with the simplest molecular formula. The formation of the tetramer (SeCl) 4 , [ 5] with delocalized sigma bonding of the bridging chloride is clearly preferred over a “hypervalent” small molecule. Gaseous cyclic 4 containing ClX 2 and chlorine, which recombines upon condensation.
Size:
The SeCl4 Lewis structure shape can be detected with the help of VSEPR theory (Valence Shell Electron Pair Repulsion Theory), which states that the electrons in the outermost orbitals of atoms are arranged in such a way that the electrons between There is minimum repulsion. Molecule. This theory assumes that, unbonded electrons (lone pair) cover more space than bonded electrons. The repulsion between lone pair-bond pair is greater than the repulsion between bond pair-bond pair. So if a central atom has a shared electron pair, the geometry of the molecule is disturbed. The hybridization of the central atom in the selenium molecule is sp3d. For this the geometry of the molecule should be a triangular bipyramid. But the central atom has a shared electron pair. The molecule has a distorted tetrahedral shape for repulsion.
Formal Fee
The electron dot structure that has a ‘zero’ formal charge is considered a constant, the structure of the molecule among all possible electron dot structures. Formal charge of an atom in the molecule = (total number of outer shell electrons – unbonded electrons – (1/2) × bond electrons))
From the Lewis structure of the molecule, we know that selenium has six electrons, the outermost orbital and chlorine has seven. Selenium atom has two unshared electrons while each chlorine atom has six unshared electrons. The formal charge for the central atom selenium is = {6- 2- (1/2×8)} = 0.
The formal charge for each chlorine atom is = {7- 6- (1/2×2)} = 0.
Since the charge on the individual atoms in the molecule is zero, the formal charge of the molecule, SeCl4, is also zero.
Pair
Lonely pairs in a molecule have such types of electrons that do not participate in bond formation. In the SeCl4 Lewis structure, there are 34 outer shell electrons, which means 17 pairs of electrons. Of these electrons, only eight electrons form the bond between the central atom selenium and four chlorine atoms. The rest are all unshared electrons.
There are thirteen pairs of electrons that do not participate in molecule formation. Each of these chlorine atoms has three pairs of that electrons and selenium has one pair of unshared electrons or lone pairs.
Hybridization
In the concept of hybridization, there is a mixture of atomic orbitals . The constituent orbitals are comparable in energy . The new hybridized orbital differs in energy with respect to the constituent orbitals. In the selenium tetrachloride molecule, consider the hybridization of only the selenium atom. It helps to determine the geometry of the molecule. In the unpaired selenium atom, it contains 4p. There are two unpaired electrons in the orbital. Also it has two electron pairs in its outermost orbital, one is in 4s orbital and the other is in 4p orbital. So it can form two bond pairs in this state.
But selenium has a ‘d’ orbital, where the paired electron from the 4p orbital can move and become unpaired. Now the 4s orbital, three 4p orbitals and one 4d orbital are mixed together. This results in the formation of sp3d hybridized orbital . Hybridized orbitals are equal in energy. Therefore the bonding overlap of the new orbital with the ligand orbitals becomes better than that of the unhybridized orbitals.
Resonance
The SeCl4 Lewis structure can have several forms. Electron dot structures are formed by the representation of shared electrons. In the selenium tetrachloride molecule, both the selenium and chlorine atoms have an unshared electron pair. They can delocalize from the parent atom and form a resonance structure. In these Lewis structures, which have ‘zero’ formal charge that would be the real configuration.
Chlorine is more electronegative than the selenium atom. Hence it can easily tolerate negative charge. There is pi(π) back bonding i.e. in 4pπ(Se) – 3dπ(Cl) molecule.
This means that the shared electron of selenium is transferred to the vacant 3d orbital of the chlorine atom. This results in the formation of a partial pi (π) bond in the molecule.
Since the non-bonding electrons of the selenium atom are involved in back bonding, the repulsion between the bonding electron pair is reduced.
Octet Rule
The octet rule deals with the electronic stability of elements in the periodic table.
All the main group elements of the periodic table like to have eight electrons in the last orbit. The tendency of completely filled orbitals in this is called the octet law. Only a hydrogen atom can have a maximum of two electrons in the orbital. This is because it has only ‘K’ orbitals. Selenium has six electrons in its outermost shell. It prefers two more electrons to the nearest noble gas like krypton . The chlorine atom has seven electrons in its outermost orbital, so it accepts that electron from the selenium atom. In this way both cover eight electrons in the outer shell. It gives stable structure to the molecule.
SECL4 Polar or non-polar
Polarity is a physical property of a molecule if the molecule has a net dipole moment generated by polar bonds.
In the selenium tetrachloride molecule, the electronegativity of selenium (Se) is 2.55 and that of chlorine is 3.16 on the Pauling scale. To account for this difference between the electronegativity of atoms, there is an uneven charge separation in the molecule. This results in a net dipole moment e and SeCl2 become polar . The ability of a covalent bond to strongly pull the electron cloud towards the atom is a measure of the electronegativity of that atom. Electronegativity gives the direction of the dipole moment. If these direction vectors do not cancel each other, a net dipole moment is produced.
In the selenium tetrachloride molecule, the selenium atom has six outermost shell electrons where as the chlorine atom has seven outermost shell electrons. The SeCl4 molecule has a total of 34 outermost orbitals in the molecule. Of these eight electrons (4 pairs of electrons) form bonds in the molecule and selenium has two unpaired electrons (one pair of electrons).
The geometry of the molecule should be a pyramidal triangle . From VSEPR theory we know that lone pair-bond pair repulsion is greater than the lone pair-bond pair repulsion. The shape of the molecule becomes distorted tetrahedral for the unpaired electron pair of the central atom selenium. For the deformed shape, the direction of the dipole moments, for the electronegativity difference, cannot neutralize each other. selenium tetrachloride becomes a polar molecule.
What is the Valency of Selenium?
The symbol for selenium is Se, atomic number 34, atomic weight 78.96, melting point 221°C, boiling point 685°C. it happens. Selenium has 6 stable isotopes and 2 radioactive isotopes known. The electronic configuration of selenium is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4.
