As you move along the period, the number of mobile electrons donated by each atom into the sea of delocalised electrons increases so that the metal becomes better at conducting electricity. Sodium, magnesium and aluminum all exist as giant metallic lattices and hence are able to conduct electricity. Electrical conductivity increases across metals.As the van der Waals forces in argon are weak, a very small amount of energy is needed to break them and therefore the melting point is low.Įlectrical Conductivity Trend Across Period 3.Argon is a noble gas and has a very low melting point as it exists as a monoatomic element consisting of very weak van der Waals forces.Therefore sulfur has the highest melting point, compared to phosphorous and chlorine. As sulfur is the largest molecule out of the three, it contains the most number of electrons and the strongest van der Waals forces.More energy is required to break stronger induced dipole-dipole forces, therefore the melting point is higher. The greater the number of electron clouds, the stronger the induced dipole-dipole forces. A larger molecule contains more electrons, therefore it consists of larger electron clouds. The stronger the induced dipole-dipole forces, the higher the melting point.The shape of a molecule and the distance between the molecules affects the strength of induced dipole-dipole forces. The melting point of these substance depends on the varying strength of van der Waals forces.For this reason, the melting points of these simple molecular substances are low. As learned earlier, van der Waals forces are weak intermolecular forces which require a small amount of energy to break.Phosphorous (P4), sulfur (S8) and chlorine (Cl2) are simple molecular substances which consist of van der Waals forces.The change in melting point from Phosphorous to Chlorine (P to Cl) ![]()
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