Why does flame test for sodium ion result in yellow flame?

Answer 1

It's because of what happens to the electrons when you heat it. (Electrons are one of the three tiny particles that make up an atom.)

The electrons in burning sodium get excited and gain energy--I would, too, if someone set me on fire--but they eventually calm down. When they calm down, they give off that extra energy as light. But here's the weird thing: They give off that energy only in certain specific amounts, most of that energy corresponds to yellow light.

Imagine a bookshelf with a sodium electron on the lowest shelf. When that electron gets excited it jumps up one or two levels of the shelf, and when it calms down it moves back down the shelf. If the next to lowest shelf is 10" inches above the lowest shelf, then the electron can move up only 10" as it goes up one level from the bottom. It can't move up just 7" because there's no shelf there. The sodium bookshelf might have a shelf that is 10" above the bottom shelf, then another shelf 8" above that and another shelf 5" above that. That means the sodium electron can move up or down 10", 8" or 5", but can't move 4" or 9".

When you burn sodium, most of the electrons move up the shelf because they gain energy, but some give off their energy very quickly and move back down again. The electrons that move down 10" from the second lowest to the lowest shelf give off yellow light. True, some electrons move down 8" from shelf #3 to shelf #2, and maybe they give off orange light, but most of the electrons are moving down 10" from shelf #2 to #1, so that's the main light that we see.

Each element has its own special bookshelf that it is restricted to, and each bookshelf has its shelves spaced differently, so as their electrons move down the different shelves they give off different colored light. Scientists can use the different colors given off to identify different elements. That's how they can identify different chemicals in space.

Answer 2

When a sodium ion is heated in a flame, the energy absorbed by the electrons causes them to jump to a higher energy level. As they return to their original energy level, they emit light in the yellow wavelength range. This yellow light is what gives the flame test for sodium its characteristic color.