Potassium is an alkali metal as potassium is in group 1 (1 valence electron). Alkali metals are highly reactive, especially highly reactive with water.
The equation of the reaction between an alkali metal and water is: Alkali metal + Water = Alkali metal hydroxide + hydrogen gas + (heat)
Most of the times, when an alkali metal reacts with water, it fizzes and sometimes even produces flame. This is because the reaction between an alkali metal and water is exothermic, and it produces enough heat to ignite the hydrogen gas.
The unique colours of the flame results from the excitement of the electrons caused by increased temperature. Excitement of an electron is when an electron temporarily has greater energy compared to its "ground state" (normal). As the reaction between an alkali metal and water is exothermic, temperature increases, and the alkali metal's electrons are in excited state. As these excited electrons return to their ground state, they release energy, which in this case, is visible light.
The colour of this visible light emitted varies due to the affinity between the outer shell electrons and atomic nucleus. For example, if we compare sodium (atomic number 11) and potassium (atomic number 19), sodium produces a yellow flame, while potassium produces a lilac flame. Since the sodium's outer shell electron is closer to its nucleus, the sodium ion has a stronger affinity for the electron, meaning that more energy is required to move/excite the electron. As this excited electron returns to its ground state, it emits more energy (as it had more energy), which means that the emitted light has a higher frequency, shorter wavelength.
In this spectrum, potassium has its unique level of affinity between the outer shell electrons and atomic nucleus, which results in emitting the wavelength of a lilac visible light.
No, I think you just need to know the fact that potassium burns with a lilac flame. (not the reasons why)
Yes, thanks for responding
Is this in the IGCSE syllabus?
Hi, thank you for your question.
Potassium is an alkali metal as potassium is in group 1 (1 valence electron). Alkali metals are highly reactive, especially highly reactive with water.
The equation of the reaction between an alkali metal and water is: Alkali metal + Water = Alkali metal hydroxide + hydrogen gas + (heat)
Most of the times, when an alkali metal reacts with water, it fizzes and sometimes even produces flame. This is because the reaction between an alkali metal and water is exothermic, and it produces enough heat to ignite the hydrogen gas.
The unique colours of the flame results from the excitement of the electrons caused by increased temperature. Excitement of an electron is when an electron temporarily has greater energy compared to its "ground state" (normal). As the reaction between an alkali metal and water is exothermic, temperature increases, and the alkali metal's electrons are in excited state. As these excited electrons return to their ground state, they release energy, which in this case, is visible light.
The colour of this visible light emitted varies due to the affinity between the outer shell electrons and atomic nucleus. For example, if we compare sodium (atomic number 11) and potassium (atomic number 19), sodium produces a yellow flame, while potassium produces a lilac flame. Since the sodium's outer shell electron is closer to its nucleus, the sodium ion has a stronger affinity for the electron, meaning that more energy is required to move/excite the electron. As this excited electron returns to its ground state, it emits more energy (as it had more energy), which means that the emitted light has a higher frequency, shorter wavelength.
In this spectrum, potassium has its unique level of affinity between the outer shell electrons and atomic nucleus, which results in emitting the wavelength of a lilac visible light.
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