[Carlo08]

Can someone give me a definition of 'Periodicity' all the places i look keep saying only ' the periodic table is based on periodicity' not actually saying what it is thanks.

[FunLady]

In science:

Periodicity in time is often specified by its frequency which has the metric units of Hertz (the number of periods per second).
Oscillations, waves and standing waves have crests at periodic intervals of space and/or time.
In physics, period is the number of cycles as a result of time (time/cycle). The amount of time it takes to complete one full revolution. Period is also the inverse of frequency.
In mathematics, a periodic function is a function whose output contains values that repeat periodically.
In mathematics, in group theory, a periodic group is a group in which each element has finite order.
In chemistry, the periodic table is a table which classifies the chemical elements by means of the periodicity of their chemical properties.

[mathslover786]

periodicity is just trends in the periodic table ie as you go across the periodic table the atomic radii decrease and nuclear charge increases due to 1 more proton....

[Carlo08]

So would it be enough to describe as : The trends encountered whilst moving accross the periodic table in various directions?

[Preasure]

'The trends and patterns in physical and chemical properties seen in the different blocks, rows and groups of the periodic table' might be better.

[Carlo08]

Originally Posted by Preasure

'The trends and patterns in physical and chemical properties seen in the different blocks, rows and groups of the periodic table' might be better.

Thanks

I noticed you do chemistry and was wondering if youk now how to do this question:

i have a table of energy levels and values for h+

So :

N = 1, 2, 3, 4, 5 , 6 , 7
E= 0, 6.54,7.75, 8.16, 8.34, 8.47, 8.54 all in 10^-18 j

How do i work out which jumps give lines in the visible region? how do i draw an energy level diagram for this? and finally how do i estimate the ionisation energy for h+

Thanks so much if you or anyone else can answer this, i will rep until the day i leave tsr :p

[Preasure]

Physical chem isn't my best area but I'll have a go:

First of all, you'll need to work out the change in energy for each transition from one energy level to the next one up (so the E2-E3 transition is given by 7.75-6.45), and work out the frequency of these transitions using the Bohr-Einstein condition: change in E = hv where h is Plancks constant and v is frequency in Hz. Once you've done this see which fall inside the visible part of the spectrum - 4.3 x 10^14 to 7.1 x 10^14 Hz.

The ionisation energy is the energy required to remove 1 mole of electrons - multiply the energy transition of E0 to E1 by avagadro's number.

Correct me if I'm wrong, it's kind of a weak area for me.

[Carlo08]

Originally Posted by Preasure

Physical chem isn't my best area but I'll have a go:

First of all, you'll need to work out the change in energy for each transition from one energy level to the next one up (so the E2-E3 transition is given by 7.75-6.45), and work out the frequency of these transitions using the Bohr-Einstein condition: change in E = hv where h is Plancks constant and v is frequency in Hz. Once you've done this see which fall inside the visible part of the spectrum - 4.3 x 10^14 to 7.1 x 10^14 Hz.

The ionisation energy is the energy required to remove 1 mole of electrons - multiply the energy transition of E0 to E1 by avagadro's number.

Correct me if I'm wrong, it's kind of a weak area for me.

Thanks, also can an electron only jump one level at a time? So i just check each single jump say 1-2 2-3 3-4 .... or do i have ot look at all the combinations so 1-2 1-3 1-4 etc?

[Preasure]

There's too many combinations to make you do all of them, electrons can jump a level if given the right amount of energy. Perhaps work out the energies at the top and bottom of the visible region and then work backwards from that? Then you won't need to work out any frequencies.

[charco]

Originally Posted by Carlo08

Thanks

I noticed you do chemistry and was wondering if youk now how to do this question:

i have a table of energy levels and values for h+

So :

N = 1, 2, 3, 4, 5 , 6 , 7
E= 0, 6.54,7.75, 8.16, 8.34, 8.47, 8.54 all in 10^-18 j

How do i work out which jumps give lines in the visible region? how do i draw an energy level diagram for this? and finally how do i estimate the ionisation energy for h+

Thanks so much if you or anyone else can answer this, i will rep until the day i leave tsr :p

Graph the values to find the approximate highest energy value (where the curve flattens out) and this corresponds to the transition from n= infinity to n=0. This is numerically equal to the ionisation energy per electron. Multiply by Avogadro's number to get energy per mole.

The visible transitions are those from all n values (except n=1) to n=2. Find the difference in energy between the higher value and that of n=2 and use the formula E= h x c/wavelength to find the wavelength for each transition. Get the colour from the wavelength.

[Carlo08]

Originally Posted by Preasure

There's too many combinations to make you do all of them, electrons can jump a level if given the right amount of energy. Perhaps work out the energies at the top and bottom of the visible region and then work backwards from that? Then you won't need to work out any frequencies.

So ive done E=hv for the top and bottom giving me : 2.85 and 4.70x10^-19

So now do i just find all the combinations on the change in energies that fit between these? so far all i can find is the gap from 3-4 which is 0.41x10^-18 which goes to 4.1x10^-19 which fits between the range.

[charco]

Originally Posted by Carlo08

So ive done E=hv for the top and bottom giving me : 2.85 and 4.70x10^-19

So now do i just find all the combinations on the change in energies that fit between these? so far all i can find is the gap from 3-4 which is 0.41x10^-18 which goes to 4.1x10^-19 which fits between the range.

read my post above - it explains what you have to do!

[Carlo08]

Originally Posted by charco

Graph the values to find the approximate highest energy value (where the curve flattens out) and this corresponds to the transition from n= infinity to n=0. This is numerically equal to the ionisation energy per electron. Multiply by Avogadro's number to get energy per mole.

The visible transitions are those from all n values (except n=1) to n=2. Find the difference in energy between the higher value and that of n=2 and use the formula E= h x c/wavelength to find the wavelength for each transition. Get the colour from the wavelength.

When you say graph the values, is this an energy level diagram as this is the first part of the question?

[charco]

Originally Posted by Carlo08

When you say graph the values, is this an energy level diagram as this is the first part of the question?

A simple graph of energy level (x axis) against energy (y axis) will tend towards flat. When the slope = 0 you have reached the maximum energy possible for a transition - this is equivalent to the ionisation of 1 electron.