Describe the physical and chemical properties of the elements of group $17$.

(N/A) The halogens show a regular gradation in their physical properties. Fluorine and chlorine are gases,bromine is a liquid,and iodine is a solid.
Their melting and boiling points increase regularly with an increase in atomic number.
All halogens are coloured. This is due to the absorption of radiation in the visible region,which results in the excitation of outer electrons to higher energy levels. By absorbing different quanta of radiation,they display different colours.
For example,$F_2$ is yellow,$Cl_2$ is greenish-yellow,$Br_2$ is red,and $I_2$ is violet. Fluorine and chlorine react with water. Bromine and iodine are only sparingly soluble in water but are soluble in various organic solvents such as chloroform,$CCl_4$,$CS_2$,and hydrocarbons to give coloured solutions.
Bond dissociation enthalpy of $F_2$ is lower than that of $Cl_2$,whereas the expected trend in bond dissociation enthalpy for $X-X$ bonds after chlorine is: $Cl-Cl > Br-Br > I-I$.
This anomaly is because the electron-electron repulsions among the lone pairs in $F_2$ are relatively larger than in $Cl_2$ due to the smaller size of the fluorine atom.
Chemical Properties:
Trends in oxidation states and chemical reactivity:
All halogens exhibit a $-1$ oxidation state. However,chlorine,bromine,and iodine also exhibit $+1, +3, +5$,and $+7$ oxidation states.
Higher oxidation states of chlorine,bromine,and iodine are realised mainly when the halogens are in combination with the small and highly electronegative fluorine and oxygen atoms.
For example,in interhalogen compounds,oxides,and oxoacids. In oxides and oxoacids of chlorine and bromine,$+4$ and $+6$ oxidation states are also observed.
Fluorine atom has no $d$-orbitals in its valence shell and therefore cannot expand its octet. Being the most electronegative,it exhibits only a $-1$ oxidation state.
All halogens are highly reactive. They react with metals and non-metals to form halides. The reactivity of halogens decreases down the group.
Due to their ability to accept electrons easily,halogens act as strong oxidising agents. $F_2$ is the strongest oxidising halogen and it oxidises other halide ions in solution or even in the solid phase.
In general,a halogen oxidises halide ions of higher atomic number.
$F_2 + 2X^- \rightarrow 2F^- + X_2$ (where $X = Cl, Br$ or $I$)
$Cl_2 + 2X^- \rightarrow 2Cl^- + X_2$ (where $X = Br$ or $I$)
$Br_2 + 2I^- \rightarrow 2Br^- + I_2$