All round us we have Chemical compounds – they are in our beverages, food and in items one uses day to day. We can identify these chemical compounds by their molecular formulas. Though the molecular formula demonstrates how many atoms there are for every element existing in the compound, it does not communicate to us about by what means the elements are attached to each other. We have no idea which atom of an element is attached to which. This is the place where the structural formula arises. It displays how the atoms are organized and attached together in a molecular formula of a chemical compound. Deprived of the structural formula, one would not discern that acetic acid has a carbon atom double-bonded together with oxygen. One can see the spatial arrangement of the atoms in the compound, by taking a look at the formula.
For example, hexane has a molecular formula of C
14 , or structurally CH
3 , implying that it has a chain structure of 6 carbon atoms, and 14 hydrogen atoms. However, the empirical formula for hexane is C
7 . Likewise the empirical formula for hydrogen peroxide , H
2 , is simply HO expressing the 1:1 ratio of component elements. Formaldehyde and acetic acid have the same empirical formula, CH
2 O . This is the actual chemical formula for formaldehyde, but acetic acid has double the number of atoms.
As mentioned initially, for structural bolting, it is not valid to use published values based on a torque-tension relationship. In other words, you cannot use torque from a formula. The calibrated wrench method is only valid if installation procedures are calibrated on a daily basis by tightening not fewer than three representative fastener assemblies (typical) for each lot, diameter, length, and grade with nuts from each lot, diameter, and grade and with a hardened washer tightened in a device (Skidmore-Wilhelm) capable of measuring actual bolt tension.