HL Chemistry Electron Arrangement

Objectives 2.3.1Describe the electromagnetic spectrum Distinguish between a continuous spectrum and a line spectrum Explain how the lines in the emission spectrum of hydrogen are related to electron energy levels Deduce the electron arrangement for elements Z=1-20 (this is an old objective)

So how do we know anything about how atoms are put together?

“The study of emission of “light” by atoms and ions is the most effective technique for deducing the electronic structure of the atom.”  In this case, the term “light” is used to indicate electromagnetic radiation.  Which end of the spectrum has the highest energy per quanta? Lowest?

Long story short, we excite electrons and wait for them to fall back to their ground state. This process releases the “light” that we are looking for.  How do you get electrons excited?

rogenspectrum.jpg

The spectra of the light emitted comes in 3 categories.  We generally look at emission (or line) spectra to study the electrons in an atom.

What is the relationship between electrons and line spectra?  Read the bottom part of page 55 in your text to answer that question.

What is the relationship between electrons and line spectra?  What does the presence of line instead of continuous spectra tell us about atoms?

“By studying the frequencies of the lines in the emission spectrum of an element, the energies of the various energy levels within the atom can be found.”  Make some observations

“By studying the frequencies of the lines in the emission spectrum of an element, the energies of the various energy levels within the atom can be found.”  Each element gives off it’s own characteristic line spectra.  The energy levels are not evenly spaced.

 The diagram on the right shows the line spectra of a hydrogen atom predicted by the current theory.  It nicely matches reality (below) for once…

 Come up with an explanation for why the energy differences seem to decrease between successive energy levels.

astr.gsu.edu/hbase/hyde.html

ges/hydrogen_spectrum.gif ges/hydrogen_atom_energy_level s.jpg

For more info on the spectra of a hydrogen atoms go to: properties/hspectrum.html properties/hspectrum.html

Electronic Arrangement – is a simplified method of thinking about electrons that only concerns itself with energy levels (and not orbitals). You should be able to predict these “electron structures”.

Take a look and then we’ll practice a few.

Self Check Time 2.3.1Describe the electromagnetic spectrum Distinguish between a continuous spectrum and a line spectrum Explain how the lines in the emission spectrum of hydrogen are related to electron energy levels Deduce the electron arrangement for elements Z=1-20 (this is an old objective)

Homework (Due Friday)  Read Section 2.3 in Green/Damjii  Do Ex 2.3 on pp # 1-10  DUE on Friday, Sept 21.

Optional  Write a paragraph that will explain how the lines in the emission spectrum of hydrogen are related to electron energy levels. Feel free to use any resources that you choose. Just cite them.