bohr model atom - Mrs. Rorabeck's VCI...
Transcript of bohr model atom - Mrs. Rorabeck's VCI...
Bohr's Model of the Atom
The gateway to our current ideas about atoms
SCH 3U0/4C0
[physicsoftheuniverse.com]
Back to Thomson...
JJ Thomson [wikimedia]Thomson's cookie model. Mmmm, cookies
[dipity.com]
...And Rutherford
Rutherford [nobelprize.org]Tossing cookies? Ewww.
[reich-chemistry.wikispaces.com]
[blogspot.com]
Problems with Rutherford's Model
● Electrons in orbits radiate.● When they give off radiation, they lose
energy.● When they lose energy, they slow down.● When they slow down, they fall into the
nucleus.● When they fall into the nucleus, the atom
ceases to exist.
Rutherford's Problems (cont'd)
● So Rutherford's model says all atoms should collapse.
● Problems with this? Look around you!
Atomic collapse looks like this.[salishsea.typepad.com]
Bohr's Solution
● Electrons aren't particles in orbits (like planets round the sun): they're waves!
● These electron waves can't have any old orbit: they only orbit at certain allowed distances. The simplest electron wave around
a nucleus.
Bohr's Solution (cont'd)
The second simplest electron wave The third simplest electron wave
Bohr's Solution (cont'd cont'd)
● Electron waves are only allowed at distances where their wave joins up “nicely”.
Nice on the left. Not nice on the right. What dowe mean when we say nicely? [wikimedia]
[astro.queensu.ca]
Proof of Bohr's Model
● Electrons can only have certain orbits.● Because only certain orbits are allowed,
they can only give off certain colours: i.e., spectroscopy!
● No other model could predict that atoms should have discrete spectral lines.
Spectroscopy
Is used to identify the compositions of stars, for example [astro.queensu.ca]
Names For Where Electrons Wave Around Atoms
● The places where electrons wave around an atom is called an orbital.
● These orbitals occur in energy levels.● There are four kinds of orbitals.● Each orbital can be made up of
suborbitals.
Details About spdf Orbitals
● s holds up to 2 e-; 1 suborbital.
● p holds up to 6 e-; 3 suborbitals.
● d holds up to 10 e-; 5 suborbitals.
● f holds up to 14 e-; 7 suborbitals.
There are other orbitals, but we won'tneed or see them in this course. How manyelectrons does each suborbital hold up to?
Filling Orbitals with Electrons
The filling order diagram. Being a littleconfused at this point is normal.
● The number in front of each orbital is called the energy level.
● Follow the arrows, one at a time, from the top down, to put electrons around any atom.
How Many Electrons are in an Atom?
JIC: The atomic number is the one in red.
● Look at the atomic number.
● How many electrons are in an atom of H? He? C? U? F?
● Then we use the filling order diagram to place the electrons.
Electron Configurations (ECs)
● Use the filling order diagram.
● How are electrons arranged around an atom of: H? Li? C? Fe? Cu? Lr?
● These arrangements are called electron configurations (ECs)
[chemtutor.com]
[jamesannjo.wordpress.com]
Lies I Was Told?
● What happened to “the first shell holds two, the second shell holds eight, the third shell holds [depends], and don't go past element 20?”
● How many does the third “shell" hold? The fourth?
● For those not afraid of math: number of electrons in a “shell” is 2n2, where n is the energy level (“shell” number).
Truths to Still Hang on To?
● Remember valences? Valences are how many electrons an atom wants to gain or lose to be stable.
● What does “stable” mean? In grade 9/10, full or empty.
You can tell the number of valenceelectrons for non-transition metals
directly from the PT [kgortney.pbworks.com]
Predicting Valences for Non-Transition Metals with ECs
● Use the ECs we've already constructed to make sense of the valences for those elements.
Go one more column, and predict valences [sparknotes.com]
[chemwiki.ucdavis.edu]
Transition Metals: Multivalent Atoms (MVAs)
● Cu is one or two;
Fe is two or three;
Hg is two or four;
Some MVAs; there are many more.● Use their ECs to make sense of their
valences.
And – as Always – There's a Pattern to Things
What is it about this pattern that allows the transition metals to bemultivalent? [chemwiki.ucdavis.edu]