Covalent bonds and valence
The water molecule always has a composition in which two hydrogen atoms combine with one oxygen. Why? The Lewis structure in Figure 2.11 represents water, H2O. Oxygen is element number…
Breaking bonds requires an input of energy
A plant accumulates nutrients from the soil as it grows. Such accumulation depletes the amount of nutrient remaining in the soil; so, harvesting an arable crop, such as maize, barley…
Hydrogen bonds
DNA is a natural polymer. It was first isolated in 1869 by Meischer, but its role in determining heredity remained unrecognized until 1944, by which time it was appreciated that…
Elastic and inelastic collisions
In the previous example, we looked at the interactions induced when changing the external pressure, forcing the molecules into close proximity. We look here at the effects of changing the…
How is ammonia liquefied?
Compressing ammonia gas under high pressure forces the molecules into close We sometimes call a solid or a liquid a ‘condensed phase’. proximity. In a normal gas, the separation between…
The Maxwell–Boltzmann distribution of energies
If no heat was distributed, then our faces and those parts closest to the fire We often see this relationship called merely the ‘Boltzmann distribution’, after the Austrian Physicist Ludwig…
Motion of particles in the gas phase
The question, ‘What is pressure?’ is another odd question, but is not too difficult to answer. The constituent particles of a substance each have energy. In practice, the energy is…
The ideal-gas equation
A bubble-jet printer is one of the more useful and versatile inventions of the last decade. The active component of the printer is the ‘head’ through which liquid ink passes…
The effects of temperature on density
The air around a hot radiator soon acquires heat. We explain this observation from the ‘minus oneth law of thermodynamics’ (see Section 1.1), since heat travels from hot to cold.…
‘The material of action so variable’
The classical author Epictetus (ca 50–ca 138 AD) once said, ‘The materials of action are variable, but the use we make of them should be constant’. How wise. When we…
