Fluorine is the strongest oxidising agent and oxidises other halide ions in solution or even in the solid phase. Therefore, it is most reactive among the halogens. Halogens have high electron acceptance property and therefore they have strong tendency to take up the electron :Īs a result, they act as powerful oxidising agents. This is due to weak F-F bond because of the repulsion between the non-bonding electrons in the small molecule. Thus, halogens are very reactive elements due to their low dissociation enthalpies and high negative electron gain enthalpies. Fluorine has the lowest bond dissociation enthalpy. Halogens have very high negative electron gain enthalpy values and therefore, have very strong tendency to gain an electron. As a result, they can readily dissociate into atoms and react with other substances. The high reactivity of halogens is due to the following reasons :Īll the halogens have very low dissociation enthalpies. The reactivity of the halogens decreases down the group. Fluorine is the most reactive of all the halogens. The halogens react readily with metals and non-metals to form halides. 1.4 (4) Reactivity of Halogens towards Halogens.
H-F is a weak acid (~2.5% ionized) in aqueous media where as HCl, HBr & HI are strong acids ionizing 100% in aqueous media b/c of decreasing H/X bond strengths. The numerical values (supported by many online references) are. As a result the bond energy trends, from strongest to weakest follow H-F > H-Cl > H-Br > H-I. As atomic number increases additional energy levels are present causing a shielding effect that reduces the influence of the nucleus on the valence level electrons. Such is why the trend is called 'The Hydrogen Halide Paradox'.
Halogen reactivity series#
The bonding energies of the H-X series are 'size of halide ion' dependent, not 'electronegativity' dependent as in series substances.
'Down' the group the strength of H-X bonds decrease and form weaker bonds giving up 'less' energy on formation. As a result due to difference in energy requirements the reactivity of H-X is higher up the group The acidity of the Hydrogen - Halide group is also referred to as the 'Hydrogen Halide Paradox'Ĭan you please also tell me what role does the bond enthalpy of H-X plays in the reactivity trends of halogens towards hydrogen?ĭown the group the strength of H-X bonds increases and to form a strong bond more energy is required. The order of increasing electronegativity is C (H - Cl) > (H - Br) > (H - I) due to the addition of principle energy levels (rings) creating a 'shielding effect', 'Shielding' decreases the electrostatic influence of the nucleus on the bond between the valence of the anion and the attached substrate. Ionizations follow the same trends in series for the Group I - III elements, but C, N, O & F tend to gain electrons causing a large in crease in ionic radius after Boron because of e-/e-repulsion, but electronegative effects still increase from Carbon through Fluoride. The effect of increasing electronegativity of neutral elements in series functions to decrease atomic radius b/c of increased force of electrostatic attraction. Electronegativity increases with increasing atomic number due to increasing number of electrons and protons making up the atomic and ionic structures. In series (consider Series II => Li, Be, B, C, N, O, F & Ne). Bond Energy trends are a function of electronegativity in series and of ionic size in groups.
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