Molecular Geometry, Hybridization, Polar or Nonpolar

HCN Lewis Structure, Molecular Geometry, Hybridization, Polar or Nonpolar HCN, or hydrogen cyanide, is a colorless, highly toxic, and combustible chemical compound. At 25.6 °C, it boils slightly above room temperature. HCN is a versatile substance since it is utilized as a highly valued precursor to a variety of chemical compounds ranging from polymers to medicines, as well as in other industrial sectors. On a large scale, HCN is used to produce potassium cyanide and adiponitrile, which are utilized in the manufacture of plastics and mining. Hydrogen cyanide is extremely toxic and combustible. Exothermic oligomerization occurs when distilled HCN is heated, hence it should be maintained at temperatures considerably below its melting point. Hydrogen cyanide, a chemical asphyxiant, is a systemic asphyxiant. It prevents nearly all of the body's organs from using oxygen normally. In a matter of minutes, hydrogen cyanide poisoning can be fatal. It affects the central nervous system (brain), the cardiovascular system (heart and blood vessels), and the pulmonary system, which are the organ systems that are most sensitive to low oxygen levels (lungs). Hydrogen cyanide is a chemical weapon (military designation, AC). Commercial uses of hydrogen cyanide include fumigation, electroplating, mining, chemical synthesis, and the production of synthetic textiles, plastics, dyes, and pesticides. Because of its acidic behavior in water and its derivation from Prussian blue, hydrogen cyanide was given the German term Blausäure ("Blue acid") by the Swedish chemist Carl Wilhelm Scheele in 1782. Prussic acid acquired the common name for it in English. Properties of Hydrogen cyanide ➢ HCN is a colorless, highly poisonous, and flammable liquid. ➢ HCN is used as a highly valued precursor to many chemical compounds from polymers to pharmaceuticals. ➢ It has the odor of oil of bitter almond. ➢ It has a molar mass of 27.0253 g/mol and density of 0.6879 g/cm3. ➢ The melting point and boiling point of HCN are -13.29°C and 26°C respectively. Preparation of HCN At roughly 1,200 °C (2,190 °F), methane and ammonia react in the presence of oxygen over a platinum catalyst: 2 CH4 + 2 NH3 + 3 O2 → 2 HCN + 6 H2O Small amounts of HCN are created in the laboratory by adding acids to cyanide salts of alkali metals: H+ + NaCN → HCN + Na+ HCN Lewis structure Chemical bonds are usually always created by atoms' valence electrons interacting with one another. To understand how valence electrons interact, Gilbert N. Lewis devised a simple manner of visualizing them in 1916. A Lewis structure is a molecule's structural depiction in which dots represent electron locations surrounding atoms and lines or dot pairs represent covalent bonds between them. It assists in determining the chemical bond formation and identifying lone pairs of electrons in molecules. Covalently bound molecules and coordination compounds can both be represented by Lewis structures. Lewis dot diagrams, electron dot diagrams, Lewis dot formulae, and electron dot formulas are all terms used to describe Lewis structures. Technically, Lewis structures and electron dot structures are different because electron dot structures show all electrons as dots, while Lewis structures indicate shared pairs in a chemical bond by drawing a line. Valence electrons The number of electrons in an element's outermost shell determines the valency of the element. As a result, valence electrons refer to an atom's valence shell and the electrons that correspond to it. The valence electrons of all three atoms i.e hydrogen, carbon, and nitrogen, must be determined here to find the valance electrons of HCN. In the modern periodic table, Hydrogen has only one valence electron because it is an exception atom that does not follow the octet rule and hence does not require eight electrons to fill its octet but only one. Similarly, Carbon has four valence electrons and Nitrogen has five in its outermost shell. Octet Rule The octet rule is a chemical concept that states that in order to maintain stability, atoms will tend to fill their energy level with eight electrons. In 1917, American physicist Gilbert Newton Lewis proposed the octet rule. Lewis noticed that by mingling with one another, atoms try to achieve the structural configuration of the Noble gas, which is closer to the periodic table of elements. Formal charge The formal charge of an atom is a quantity that indicates whether the atom is electrostatically balanced or not. The formula below can be used to determine the formal charge of any chemical. Formal Charge = Valence electrons – Unbonded electrons – Half of the bonded electrons Steps for drawing Lewis dot structure of HCN Step 1. Count the total number of valence electrons present on each atom of the HCN compound. The valence electrons of all three atoms i.e hydrogen, carbon, and nitrogen, must be determined here to find the valance electrons of HCN. In the modern periodic table, Hydrogen has only one valence electron because it is an exception atom that does not follow the octet rule, and to fill its octet it needs only one electron. Similarly, Carbon has four valence electrons and Nitrogen has five in its outermost shell. Therefore, the valance electrons of HCN are the total summation of the valance electrons of hydrogen, carbon, and nitrogen. Mathematically, Valance electrons of HCN= valance electrons of a Hydrogen+ valance electron of carbon + valance electron of Nitrogen Valance electrons of HCN= 1+4+5=10 Hence, the valance electrons present in HCN are 10. Step 2. Determine the total number of valence electrons pairs for the HCN compound. The sum of sigma bonds, pi bonds, and lone pairs present at the valence shells equals the total valence electrons of the molecules. Mathematically, Total valence electrons = sigma bonds+pi bonds+lone pairs at valence shell, However, dividing the total valance electrons by two yields valence electron pairs, which is a simple calculation. Therefore, in the case of HCN, the total number of valance electrons pairs will be 10/2 i.e 5. Step 3. Identify the Central atom and draw a simple skeleton diagram. An atom's ability to have a large valence is rarely required for it to be central. But, more importantly, both the number of atoms and their electronegativity must be taken into account when deciding which atom should be the center atom. Based on the Linus Pauling scale, the electronegativity of carbon(2.55) is less than nitrogen(3.04). Although hydrogen(2.20) electronegativity is less than carbon, it always goes on outside of lewis's structure. So, basically, carbon acts as a central atom while hydrogen and nitrogen are situated at the terminal ends in the lewis structure. Step 4. Put lone pairs of electrons on each atom. Lone pairs of electrons don’t share their pair of valance electrons with another atom. In the case of the HCN compound, HCN contains a total of 4 bonds in which 1 C–H single bond is formed while 1 triple bond is formed between carbon and nitrogen. Therefore, HCN has a total of 4 bond pairs. since all atoms shared the pair of electrons with central atoms, we can conclude that there are no any lone pairs of electron. Step 5. Complete the octet of all the atoms and make a covalent bond if necessary. In the lewis structure, it is very necessary for atoms of the compound to fulfill their octet state to acquire a stable state except for some exceptional elements like Boron, Beryllium, Aluminum, Hydrogen, Helium, and Lithium. In the modern periodic table, Hydrogen has only one valence electron because it is an exception atom that does not follow the octet rule, and to fill its octet it needs only one electron. Similarly, Carbon has four valence electrons and Nitrogen has five in its outermost shell. Nitrogen possessed eight valence electrons in the Lewis structure of HCN, but Carbon only had four. To build a double bond with Carbon, we'll need to shift some valence electrons from the center. After that, Nitrogen has eight and Carbon has six valence electrons. So, let's add another pair of electrons to the center atom i.e carbon. So the HCN Lewis structure still has ten valence electrons, but Nitrogen has an octet with eight valence electrons, Carbon has eight valence electrons, and Hydrogen just has two, but that's all it needs for a complete outer shell. In this way, the atoms i.e hydrogen, carbon, and nitrogen in the HCN compound acquire a stable state and fulfill its octet rule. Step 6. Calculate the formal charge distribution on all atoms and check the stability. Now, the formal charge distribution on all-atom molecules is calculated to check whether atoms are electrostatically balanced or unbalanced. Formal charge (FC) = [Valence electrons (V) – Lone pair electrons (L) -Bonded pair electrons (B)/2] Since carbon is the central atom. In carbon, it has four valance electrons, no lone pairs, and 8 bonded pairs of electrons. Mathematically, The formal charge of a Hydrogen atom in HCN= 1-0-2/2=0 The formal charge of carbon atom in HCN= 4-0-8/2=0 Since carbon is the central atom. It is not mandatory to evaluate the formal charge of the atoms at terminal ends. As the formal charge of carbon is zero. We can consider that the HCN compound is elctrostatically balanced and stable. HCN Molecular Geometry & Shape Each atom in the compound is structured in VSEPR theory in such a way that the complex becomes stable in nature, giving it a distinct shape. The molecular geometry and structure of a compound are mostly determined by lone pairs, bonding electrons. The VSEPR theory determines the molecular geometry and form of every substance. As central atom i.e carbon in HCN compound has zero lone pairs of electrons. We can predict the molecular geometry and its shape based on the AXN notation rule. AXN notation of HCN: where A represents the number of the central atoms. In this case, carbon is the central atom which means A is carbon. X represents the number of atoms bonded to the central atom. Total 2 atoms i.e hydrogen and nitrogen are bonded to the central atom carbon. So, X= 2 and N represents the non-bonding electrons (lone pair) of the central atom. In this case, carbon has zero lone pair of electrons. So N =0 Therefore, from the AXN notation of the HCN compound, the AXN generic formula of HCN is AX2N0 or simply AX2. According to the VSEPR theory, if the HCN compound has an AX2 generic formula, the molecular geometry and electron geometry will both be linear molecular geometry. The bond angle of HCN The angle generated by two covalent bonds is known as bond angles. When the central atom's electronegativity rises, electron bond pairs are drawn towards it, increasing bond repulsion and bond angles. since Hydrogen cyanide has linear molecular geometry, it results in the bond angle of 180 degrees between terminal end atoms of HCN with the central atom. Hybridization of HCN The hybridization of HCN is Sp hybridization. Hybridization is the process of atomic orbitals of an atom of nearby equal energy intermixing to generate wholly new orbitals that are equal in number to mixing orbitals, have the same shape, and have the same energy content. Calculating the bond pairs and lone pairs of atoms present in compounds can be used to detect hybridization. Or, to put it another way, we can anticipate the hybridization of any chemical based on the steps provided. If the total number of valence electrons is less or equal to 8, divide it by 2. (V.E. < 8 divided by 2) If the total number of valence electrons of a molecule is between 8 to 56, divide it by 8. (8 < V.E < 56 divided by 8) Similarly, if the valence electrons of a given molecule are more than 56, divided by 18. (V.E.>56 divided by 18) In the case of the HCN compound, the valance electrons are 10. So, it is divided by 8 yields quotient 1 and remainder 2. Since the remainder is not zero. The remainder is further divided by 2 results in quotient 1 and remainder 0. So, the total number of orbitals present in it is 2. Hence, the hybridization of HCN is sp hybridization. IS HCN POLAR OR NONPOLAR? The molecule's polarity is caused by the valence electron's non-symmetrical sharing, which results in an area of uneven charges in the molecule. Any molecule's polarity is determined by the electronegativity difference, dipole moment, and molecular geometry form. HCN is polar in nature. Although, hydrogen(2.20) has less electronegativity than carbon. It is never considered as central atoms. Based on the Linus Pauling scale, the electronegativity of carbon(2.55) is less than nitrogen(3.04). This means that the hydrogen slightly has a positive charge and nitrogen with a negative charge.The HCN molecule's H-CN bond becomes polar due to the triple bond in carbon and nitrogen (which pulls electrons from hydrogen). Due to the cancellation of the bond dipole moment in linear geometry due to the presence of one lone pair of electrons on nitrogen and a triple bond between carbon and nitrogen, the total net dipole moment of the HCN molecule is nonzero. Therefore, we can conclude that HCN is polar in nature. Electronegativity of HCN As we know, Electronegativity is a dimensionless feature of atoms in compounds that causes them to draw shared pairs of electrons towards themselves. The property of electronegativity and how it influences the polarity of compounds is shown below. ● If the electronegativity difference is greater than 1.7, the bond will have an ionic character. ● If the electronegativity difference is between 0.4 and 1.7, the bond will have a polar covalent character. ● If the electronegativity difference is less than 0.4, the bond will have a nonpolar covalent character. Based on the Linus Pauling scale, the electronegativity of carbon is 2.55 while the electronegativity of nitrogen is 3.04. Although, hydrogen(2.20) has less electronegativity than carbon. It is never considered central atoms in lewis's structure. The electronegativity difference of the central atom i.e carbon with both nitrogen and hydrogen is less than 0.5. Although this indicates that the bond will have a non polar covalent character but HCN compound is polar in nature. Summary ➢ HCN is a colorless, highly poisonous, and flammable liquid. ➢ HCN is used as a highly valued precursor to many chemical compounds from polymers to pharmaceuticals. ➢ ➢ ➢ ➢ It has the odor of oil of bitter almond. The valance electrons present in HCN are 10. The hybridization of HCN is Sp hybridization. HCN is polar in nature.