What is Hydrogen Cyanide (HCN)?
According to Ricky, a SME at Myassignmenthelp– “Hydrogen Cyanide (HCN) is a chemical compound, with the chemical formula HCN. HCN is an extremely poisonous, colorless and flammable liquid whose boiling temperature is slightly above the room temperature, at 25.6 0C or 78.1 0F“. If it is not in the liquid form then it can be in the gaseous form above 78 degree Fahrenheit. It is also known as Prussic acid, Hydrocyanic acid and Formonitrile.
All the electrons in an atom are not involved in the process of combination. The inner shell electrons are well protected and, therefore, they generally do not take part. Lewis pictured the atom in terms of positively charged ‘kernel’ (the nucleus plus the inner electrons) and the outer shell that could accommodate a maximum of eight electrons. Thus, it is mainly the electrons present in the outermost shell that take part in the chemical combinations. Therefore, these are called the valence shell electrons. G.N. Lewis, an American chemist, introduced simple notations to represent valence electrons in an atom. These notations are called Lewis symbols or electron dot symbols.
According to the Lewis notations, the symbol of the element represents the whole of the atom except the valence electrons (i.e., nucleus and electrons in the inner shells). The valence electrons are represented by the dots (.) or cross (x) around the symbol.
Significance of Lewis Structure
- The Lewis symbol indicate the number of electrons in the outermost or valence shell
- These help to predict the common or group valence of the element. For example, lithium has one electron in the valence shell and it can involve this electron in chemical combination process (by losing or sharing) and it is therefore monovalent; beryllium has 2 electrons for participating in chemical combination and is divalent. Similarly, B and C are trivalent and tetravalent because they have three and four electrons respectively. Thus, for Li, Be, B and C, the number of electrons also indicates the common valence of these elements. However, the common valence for N, O, F and Ne is equal to eight minus the valence electrons. For example, for N it is 3, for O it is 2, for F it is one and for Ne it is 0. Thus, the common valence of an element is either equal to the number of dots in the Lewis symbol or it is equal to 8 minus the number of dots.
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