modern atomic theory, chemistry

8/13/2019 Modern Atomic Theory, Chemistry

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Modern Atomic Theory ACloserLookAtEnergyLevels



The Wave Mechanical Model

• After Bohr's model was presented, experiments confirmed

that the electron has properties both of a particle (mass)and of light (wave nature). Because of its dual nature, the

electron could not be viewed as a simple particle circling the

nucleus at a definite distance.

• If the electron moved with a high velocity, as Bohr had

claimed, one couldn't know its location with match

certainty.

• The faster a particle moves, the less we would know about

its location.

– This is analogous to a fastball thrown by a professional

baseball pitcher. The faster the ball is thrown, the less the

batter knows about its location and the less likely that the ball

will be hit.



•

Wave mechanics is the wave natureof electron and the uncertainty of itslocation led to a complexmathematical approach to theelectron in the hydrogen atom.

• In the wave mechanical model, onlythe probability of finding theelectron in a given region of spaceat a certain instant could bedetermined.

• Bohr calculated the exact radius of

the ground-state energy level forthe electron in hydrogen. In thewave mechanical model, this radiusrepresents the highest probability of finding the electron.

The electron density of the

ground state of hydrogen is

spherical.



The First Shell and s Orbitals

• An orbital is the region of space

where there is the significant probability of finding of a particular

electron. (Note that this is a different

concept from Bohr's orbits.)

–

Sometimes viewed as an "electroncloud," as if the electron were spread

out in a volume of space like a cloud.

• In the figure shown, the sphere is

understood to represent a volume of

space containing about 90% of the

electron density.

The s orbitals are

represented asspheres.



• An s orbital is a spherical volume of probability (the

electron cloud).• The energy levels, or orbits, that Bohr described do have

meaning in our modern approach but are now known as

shells

–

The first shell in hydrogen (n=1), which is known as theground state of hydrogen because it has the lowest energy,

contains only the one spherical s orbital. Normal, that's the

state occupied by the hydrogen's single electron.



The Second Shell and p Orbitals

•

The second kind of orbital present in the second shell isshown as a p orbital and has two regions of high

probability, called lobes, on either side of the nucleus .

• The electron distribution in a p orbital is not spherical

but is shaped much like a weird baseball bat with two fat

ends.

• The difference between s and p orbital is analogous to

dorm rooms that have different dimensions and shapes.



In a three-coordinate graph, if we define x as the

axis along which the two lobes of a p orbital are

directed, we can designate that p orbital as the p x

orbital. The other two p orbitals are each at 90° anglesto the p x orbital and each other. They are referred to

as p y and the p z orbitals. The surfaces that represent

about 90% of the electron density of the p orbitals are

in the Figure shown.

Each p orbital has two lobes



• The second shell has a four regions of space that may

contain electrons - one s orbital and three p orbitals.

• The orbitals of the same type in each shell make up what

is referred to as a subshell

– A subshell is labeled with a number corresponding to the shell

(1,2,3, etc.) and the type of orbital labeled that makes up that the

subshell (s,p ,etc.).

• The first shell has only a single s subshell, which is called

the 1s. The second shell contains an s subshell (the 2s )

and a p subshell (the 2 p ), which is made up of three

individual p orbitals.



Outer Shells with and f Orbitals

Except for the d z2 , the d orbitals have four lobes.



There are three subshells containing a total of nine orbitals in the

third shell.

The third shell(n = 3 )

3s 3 p 3d

s subshell p subshell

d subshell



• The third shell has three

types of orbitals, or threesubshells.

– Like the first two, it has a

spherical 3s orbital and

like the second level ithas three different 3 p

orbitals.

• The third type of orbital

found in the third shell isknown as orbitalEach successive shell

has one additional shell



• The fourth shell (n=4) has all the

same types of orbitals as the

third shell (i.e., one 4s , three 4 p ,and five 4d orbitals) and one

additional type known as an f

orbital

• In atoms with more than one

electron, the energy of the

subshells within a shell is not the

same and increases in the order

s < p < d < f

increasing energyThe subshells within a

shell have different

energies.



• The capacity of electrons in a subshell is determined

by the number of orbitals in that particular subshell.

Each orbital can hold two electrons.

1

2

3

4



That's All!



Prepared ByRios Lyndon

Rosales Eldhie Ann E.

Sabanal Karen

Saranza Ricardo

Tangga-an Kimberly

modern atomic theory, chemistry

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