Question

Na+ ion gives Golden Yellow colour to the flame when we experiment the Flame Test .

But then the FLAME OF THE FIRE TREMBLES. It happens just with Na+ ion. Why it trembles ?

Give me reason. Please help .

Answer 1

The question is same as the question why Nacl gives yellow intense colour in flem test.Usually sodium in atomic form has its outer electron risen in energy level by the heat of the flame. The electron falling back to a normal energy level emits light (reflects light?) in a specific wave length.

In sodium chloride the sodium is in its ionic form thus has no outer electron.
In a flame there are enough free electrons for sodium to pick one up so in its atomic form the mechanism explained above can happen.The chloride donates the electron from the sodium back. ven this qualitative result aleeady tells you a lot, namely that most of the emission comes from neutral sodium, not from chlorine/chloride, a fact that you can confirm quantitatively by looking at the strength of the emission lines. Likewise, when you change the anion, a flame test will almost always show the same yellow glow, showing that emission only occurs from sodium, it indicates that the most likely mechanism is the second one that you list, which occurs in two steps, starting with 1) the transfer of one electron from one chlorine atom to a sodium ion, creating an excited neutral sodium atom, which then 2) releases its excess energy by emitting light. You can jot down the diagram as follows:

Na+ + Cl- + heat -> Na* + Cl -> Na + Cl + light,

where the asterisk shows that the sodium atom is excited in the second step, and relaxes by emitting light.

The reason this pathway dominated îs because it requires the least amount of energy. Now it is true that if you pump more and more energy into the system, you can create a sufficiently hot energy bath that you start populating other excited states, which then would lead to a complicated mess where you can get emission from both Na, and Cl in various charged states. However, at the (relatively low) energies you can achieve by using a low temperature flame test, this second mechanism is less likely to happen.