Chemistry Questions

[Hielly]

heys,
got stuck on these questions.

1) Explain the relationship between the group number and the number of
electrons in the valence shell.

2) Explain why an atom of caesium is larger than an atom of sodium.
(is it , when you go down the period it decreases and also when you go down the group it increases?)

3) If the flame spectra of calcium chloride, calcium
carbonate and calcium nitrate were observed,
would you observe one main colour or three?

4) Sodium vapour street lights emit a characteristic
yellow light. Explain this.

5) An atom has several excited states but only one ground state. What does this mean?

6)Also, for the electron cinfiguration is it 2,8,18.... or 2,8,8....
thanks

[iamdan08]

1) The group number is the number of electrons that are present in the outer (valence) shell. This is the relationship between the two.

2) The caesium atom is bigger because as you go down the group, the atom contains more electron shells and more protons and neutrons in the neucleus. The atoms get bigger as you go down the group and across the period.

3) One main colour. The calcium metal is what emits the light.

[TrueTears]

Q5, An atom only has 1 ground state. ground state just means the shell which the electron is normally in. Take carbon for example, it has 2 electrons in the first shell and 4 electrons in the next shell. These shells where the electrons belong in are the ground states. However an excited state means when a certain amount of energy is applied to that element, the electrons will 'jump' to a higher shell(aka energy level). This depends on the amount of energy that is applied to the element, so it can jump to any higher shell depending on the amount of energy it is given. But there is only 1 ground state which it can return to, ie the original shell it came from before jumping to a higher shell.

[Hielly]

thanks guys! hey iamdan08, can you explain further for q.3 why do you only see one colour? and whats does calcium metal have to do with it?

[TrueTears]

thanks guys! hey iamdan08, can you explain further for q.3 why do you only see one colour? and whats does calcium metal have to do with it?

The metal is the important part. Each element has its own distinctive emission spectrum. The chloride, carbonate and nitrate parts do emit light, but they are not in the visible regions of the electromagnetic spectrum, or if the flame is not hot enough, it won't be enough to "excite" the electrons to a higher energy level, hence no light will be emitted. Hence the only colour you will see is the colour emitted by Calcium which is mainly red, (and a few lines of purple/violet colour)

[iamdan08]

4) Well as TrueTears said above, "each element has its own distinctive emission spectrum" and in the sodium vapor lamp, it is the sodium metal in the lamp that emits this spectrum. Since the light emitted is in the visible region of the spectrum, it emits what we see as yellow light. The reason that it is yellow is because sodium's "distinctive" colour is yellow. I'm pretty sure you're not required to know the actual construction of the lamp and how the sodium atoms are excited, just the fact that they are and as a consequence yellow light is emitted.

[TrueTears]

6)Also, for the electron cinfiguration is it 2,8,18.... or 2,8,8....

what do you mean electron configuration? Electron configuration for what element?

[Hielly]

the maximum electrons in the valence shells in order

[IntoTheNewWorld]

You'll have to learn about subshells to answer that question properly I think. the third shell does fill to 18, but not straight away. With the smaller elements you'll mainly deal with 8 in the 3rd shell

[Hielly]

hrm yeh i was very confused ,i came across two questions that ask abotu the electron configuration. And 1 answer said that in the first shell you have 2 then the next you have 8 etc.. but another answer said that first shell is 2 and second is 8, third is 18