Why are sodium and potassium highly reactive with water?

Answer 1

It is electron screening that accounts for the difference in the ability of the metals to react with water. When any of the alkali earth metals react with water, they are oxidized and become the positive ion of the metal. The reaction, in general, for any of the alkali metals is this, where "M" is any first row metal:

M + 2H2O --> M+ + 2OH- + H2

For all the 1st column (Group 1) metals, it is this same reaction. The further down the column you go, the more violently they react because the electronegativity of the atoms decreases down the column. Because the electronegativity is decreasing (and that is because of the increasing size of the electron orbitals and the screening of those outer electron orbitals by inner electrons), the electrons are more easily removed from the metal. That means that it is easier to form the ion, and said another way, they are more easily oxidized. That means that less energy is spent in the reaction pulling off the electron, and so the reaction is faster and more exothermic.

Answer 2

Potassium reacts very violently with water producing hydrogen gas which then usually catches fire. Potassium is usually kept under a mineral oil such as kerosene to stop the metal reacting with water vapour present in the air. Unlike lithium and sodium, however, potassium should not be stored under oil indefinitely. If stored longer than 6 months to a year, dangerous shock-sensitive peroxides can form on the metal and under the lid of the container, which can detonate upon opening. It is recommended that potassium, rubidium or caesium not be stored for longer than three months unless stored in an inert (oxygen free) atmosphere, or under vacuum.[32] As potassium reacts with water to produce highly flammable hydrogen gas, a potassium fire is only exacerbated by the addition of water, and only a few dry chemicals are effective for putting out such a fire (see the precaution section in sodium). Potassium also produces potassium hydroxide (KOH) in the reaction with water. Potassium hydroxide is a strong alkali and so is a caustic hazard, causing burns. Due to the highly reactive nature of potassium, it should be handled with great care, with full skin and eye protection being used and preferably a explosive resistant barrier between the user and the source of the potassium.

Answer 3

Well, if one of them is, then generally the other is going to be too since they're in the same group. Anyway, they're in the same group because they have the same number of valence (outer-shell) electrons: one. They both badly want to get rid of this one electron (see octet rule). As a result, both elements have low ionization energy - meaning it doesn't take much energy to knock off the electron. So when coming into contact with most substances, they will react vigorously, even with water vapor in the air - which is why they're stored in an oil (like kerosene) to prevent a reaction.

Answer 4

The valence electron in potassium has less nuclear interaction and it is able to lose electron easily as compared to sodium and hence more reactive than sodium.