What are the common physical and chemical features of alkali metals?

(N/A) Physical properties of alkali metals are as follows:
$(i)$ They are quite soft and can be cut easily. Sodium metal can be easily cut using a knife.
$(ii)$ They are light coloured and are mostly silvery white in appearance.
$(iii)$ They have low density because of the large atomic sizes. The density increases down the group from $Li$ to $Cs$. The only exception to this is $K$,which has lower density than $Na$.
$(iv)$ The metallic bonding present in alkali metals is quite weak. Therefore,they have low melting and boiling points.
$(v)$ Alkali metals and their salts impart a characteristic colour to flames. This is because the heat from the flame excites the electron present in the outermost orbital to a high energy level. When this excited electron reverts back to the ground state,it emits excess energy as radiation that falls in the visible region.
$(vi)$ They also display photoelectric effect. When metals such as $Cs$ and $K$ are irradiated with light,they lose electrons.
$(b)$ Chemical properties of alkali metals: Alkali metals are highly reactive due to their low ionization enthalpy. As we move down the group,the reactivity increases.
$(1)$ They react with water to form respective hydroxides and dihydrogen gas. The general reaction is: $2M + 2H_2O \rightarrow 2MOH + H_2$
$(2)$ They react with dihydrogen to form metal hydrides. The general reaction is: $2M + H_2 \rightarrow 2M^+H^-$
$(3)$ Almost all alkali metals,except $Li$,react directly with halogens to form ionic halides. $2M + Cl_2 \rightarrow 2MCl$ (where $M = Na, K, Rb, Cs$). Since $Li^+$ ion is very small in size,it can easily distort the electron cloud around the negative halide ion,making lithium halides covalent in nature.
$(4)$ They are strong reducing agents. The reducing power of alkali metals generally increases on moving down the group. However,$Li$ is an exception as it is the strongest reducing agent due to its high hydration energy.