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Group VII elements exist as diatomic molecules with simple molecular structure.
Going down Group VII, the molecular mass of the element increases.
An increasing molecular mass results in increasing intermolecular force of attraction.
The higher the intermolecular force of attraction, the higher the energy needed to break these bonds, hence higher melting point and boiling point.
Going down Group I, the number of electronic shells increases, and atomic radius increases. As the valence electrons get further from the nucleus, the attractive force between the positive protons in the nucleus and the negative valence electrons decreases.
Hence, going down Group I, the metallic bonding formed between the positive protons in the nucleus and the delocalized valence electrons becomes weaker.
The weaker the metallic bond, the lesser the energy needed to break these bonds, and the lower the melting point and boiling point of these elements.
Relative molecular mass is the average mass of one molecule of a substance compared to the mass of 1/12 of a carbon-12 atom.
Relative atomic mass is the average mass of one atom of an element compared to the mass of 1/12 of a carbon-12 atom.
No. of moles = Mass/ Mr or Mass/ Ar
No. of moles = Volume (dm3) x Concentration (mol/dm3)
No. of moles = Volume (dm3) / 24 dm3
Ethanol has a simple covalent structure. It exists as discrete molecules in the different states. There are no mobile ions or delocalised electrons to conduct electricity.
Metals are finite resources.
With the increasing demand for metals, our metal reserves will not last much longer.
Hence, there is a need to recycle metals to conserve the metal resources.
Recycling metals also use up less energy and produce fewer pollutants than extracting metals from their ores.
– Metal piece darts about quickly around the surface of the water
– Effervescence observed (due to hydrogen gas produced in water)
– Hissing sound heard (due to the vigorous release of hydrogen gas)
– Metal piece becomes smaller in size
– Flame observed (for some metals)
– Lithium (no flame)
– Sodium (yellow flame)
– Potassium (lilac flame)
– pH of solution increases from pH7 to pH14 (due to the formation of a strong alkali)
Heating Effect
– Infrared heating
Fires and hot bodies emit infra-red radiation. Our skin absorbs the infra-red rays, making us feel warm.
– Microwaves heating
Microwaves are of a non-ionizing character. However, microwaves, being more penetrative, can cause more severe burns to the skin, especially when skin has high water content.
Ionisation Effect
UV rays, X-ray, Gamma ray can cause breakdown of DNA, and ionization of molecules and atoms in living matter. The mutation of these cells and atoms can lead to formation of cancerous cells.