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TechnoratiTrends Across the Period (Oh no!!)
Submitted by Anonymous on 29 November 2005 - 10:36am.
Hiya people!!
I was wondering if someone could help me with a chemistry assignment. :?:
The task is to write a report on trends across the period three elements. The three trends to investigate are melting point, electronegativity and atomic radius.
For melting point, the graph goes up and down! It seems to peak at element 14 and then plummet to element 18. Does anyone know why this is, or if there's a website which could explain it?
And for atomic radius, it seems to decline across the period even when the atomic number increases. I thought it would actually increase because there are more protons :(
Any links or information would be good, thanks!!!!!
well, for melting point:
think about what happens when something melts: it changes from a solid, to a liquid.
Think about what happens to the atoms when they make that change from solid to liquid. It will require energy to make the change - how does the melting point temperature relate to that amount of energy? Why would different elements need different amounts of energy to change from solid to liquid?
For size:
well, I think you need to be able to imagine better what an atom "looks like", and where the protons are: they're in the "nucleus". The electrons are in a huge fuzzy cloud around the nucleus. If the nucleus was as big as football, then the electron cloud would probably be about the size of a football stadium! So the size of the nucleus hasn't got much to to with the size of the atom: the size of the electron cloud is more important.
Re: Trends Across the Period (Oh no!!)
As you go across a period, from left to right, you are indeed increasing the number of protons. But at the same time you are adding to the number of electrons as well. The radius of an atom is, in fact, the radius from the centre of the nucleus, made of protons and neutrons, to the edge of the atom, which is where the electrons are orbiting.
In any given period, the outer, valence, electrons are added to the same "shell", in slightly different orbitals. To a good approximation, electrons in the same shell do not repel each other - they don't shield each other. So this means that as you go across the period, each electron is seeing a bigger and bigger positive charge at the nucleus, and because they aren't being repelled by the other new electrons, they move closer to that nucleus (electrostatic attraction), resulting in the atomic radius (diameter) decreasing!
THANK YOU! I've written it up now with your help guys!!! xxxx