The Elements In Group 7 Of The Periodic Table Are Called The Halogens 2l3q2u

Physical properties of halogens The halogens show trends in physical properties down the group. Melting point and boiling point The halogens have low melting points and boiling points. This is a typical property of nonmetals. Fluorine has the lowest melting point and boiling point. The melting points and boiling points then increase as you go down the group.

Melting and boiling points of Group 7 elements State at room temperature Room temperature is usually taken as being 25°C. At this temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids. There is therefore a trend in state from gas to liquid to solid down the group. Colour The halogens become darker as you go down the group. Fluorine is very pale yellow, chlorine is yellow-green, and bromine is red-brown. Iodine crystals are shiny purple - but easily turn into a dark purple vapour when they are warmed up. Predictions When we can see a trend in the properties of some of the elements in a group, it is possible to predict the properties of other elements in that group. Astatine is below iodine in Group 7. The

colour of these elements gets darker as you go down the group. Iodine is purple, and, as we would expect, astatine is black.

Reactions and uses of halogens The halogens become less reactive as you go down the group. Fluorine, at the top of the group, is the most reactive halogen. It is extremely dangerous, causing severe chemical burns on with skin.

Reactions with metals The halogens react with metals to make salts called metal halides. metal + halogen → metal halide For example, sodium reacts with chlorine to make sodium chloride (common salt). sodium + chlorine → sodium chloride 2Na(s) + Cl2(g) → 2NaCl(s) The reaction between sodium and a halogen becomes less vigorous as we move down Group 7. Fluorine reacts violently with sodium at room temperature. Chlorine reacts very vigorously when in with hot sodium. Iodine reacts slowly with hot sodium.

Uses of halogens Halogens are bleaching agents. They will remove the colour of dyes. Chlorine is used to bleach wood pulp to make white paper. Halogens kill bacteria. Chlorine is added to drinking water at very low concentrations. This kills any harmful bacteria in the water, making it safe to drink. Chlorine is also added to the water in swimming pools. Because the halogens are very reactive and poisonous, care must be taken when using them. Chlorine is used only in a fume cupboard. Iodine should not be handled (it will damage the skin). Gloves may be used, and goggles should be worn.

The halogens are a series of nonmetal elements from group 17 of the periodic table (formerly VII, VIIA). The halogens include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The artificially created element 117 (ununseptium) may also be considered a halogen.

Atoms get bigger down the group as additional electron shells are filled. When fluorine exists as a diatomic molecule, the F–F bond is unexpectedly weak. This is because fluorine atoms are the smallest of the halogens—the electrons are bonded close together, which leads to repulsion between free electrons in the two fluorine atoms. The boiling points of halogens increase down the group due to the increasing strength of Van der Waals forces as the size and relative atomic mass of the atoms increase. This change manifests itself in the change in physical state of the of the elements from gaseous fluorine to solid iodine. The halogens are the only periodic table group containing elements in all three familiar states of matter (solid, liquid, and gas) at standard temperature and pressure Figure 1. Electronegativity is the ability of an atom to attract electrons or electron density towards itself within a covalent bond. Electronegativity depends upon the attraction between the nucleus and bonding electrons in the outer shell. This, in turn, depends on the balance between the number of protons in the nucleus, the distance between the nucleus and bonding electrons, and the shielding effect of inner electrons. In hydrogen halides (HX, where X is the halogen) the H-X bond gets further away from the nucleus as the atoms get larger. This makes the shared electrons further from the halogen nucleus and increases the shielding of inner electrons. This means electronegativity decreases down the group. Halogens are highly reactive, and they can be harmful or lethal to biological organisms in sufficient quantities. This reactivity is due to high electronegativity and high effective nuclear charge. Halogens can gain an electron by reacting with atoms of other elements. Fluorine is one of the most reactive elements in existence. It reacts with otherwise inert materials such as glass, and it forms compounds with the heavier noble gases. It is a corrosive and highly toxic gas. Fluorine's reactivity means that once it does react with something, it bonds so strongly that the resulting molecule is inert and non-reactive. Fluorine reacts vigorously with water to produce oxygen (O2) and hydrogen fluoride (HF): Chlorine has maximum solubility of 7.1 g per kg of water at ambient temperature (21 °C). Dissolved chlorine reacts to form hydrochloric acid (HCl) and hypochlorous acid, a solution that can be used as a disinfectant or bleach: Bromine has a solubility of 3.41 g per 100 g of water. It slowly reacts to form hydrogen bromide (HBr) and hypobromous acid (HBrO): Iodine is minimally soluble in water, with a solubility of 0.03 g per 100 g water. However, iodine will form an aqueous solution in the presence of iodide ion. This occurs with the addition of potassium iodide (KI), forming a triiodide ion.