Some outstanding properties of water

Consider the following series of substances methane (CH4), ammonia (NH3), water (H2O), hydrofluoric acid (HF), and neon (Ne). These substances are all isoelectronic, i.e. they all have 10 electrons (hence also 10 protons — since the molecules themselves are electro-neutral). 

Consider the series of CH4, SiH4, GeH4, and SnH4. We see that in this homologous series, the properties change regularly  

Substance Melting Point ( C) Boiling Point (°C) Molar Heat of Vaporization (calmol ) 

We see clearly that the properties of the substances HF, H2O, and NH3 have high values — far above the values that we would have derived if we extrapolated from the values of the same property of the homologous substance. This is most conspicuous for the homologous substances H2O, H2S, H2Se, and Fl2Te. 

It has also been found that the greater the electro-negativity of the ions, the stronger the hydrogen bonds. Fluoride ions form 

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