Atomic Emission SpectraAtomic Emission Spectra

Zumdahl2: p. 290-299

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What is light?

White light: reflection of all colorsBlack light: absorption of all colorsColors are each a different

wavelength (λ: lamda) of light

Colors Different wavelengths of light are seen

as different colors. Different colors indicate (show) different

energy levels.

c=fc=fλ λ (velocity of light = frequency x wavelength)

the greater the frequency the shorter the wavelength

ΔE = hfΔE = hf (energy lost by the electron = h(constant) x frequency

Frequency (and thus, color) of the light depends on the amount of energy lost by the electron.

c=fc=fλλ

When atoms are “exited” (energy is added) they produce light.

Not white or all-colored light, but one color at a time.

Study the light emitted (produced) by atoms and ions to deduce (find out) the structure of atoms.

When an atom is “excited” its electrons gain energy and move to a higher energy level. To return to a lower energy level, electrons must lose energy. They do this by giving off light.

Continuous spectrum:Continuous spectrum: all wavelengths of visible light contained in white light.

Light emitted by an atom can be separated into a line spectrumline spectrum that shows exactly what frequencies of light are present.

Closer to nucleus

Further from nucleus

Increasin

g frequ

ency

Because the light emitted from atoms is a line spectrumline spectrum (not a continuous spectrum) we determine that:

There are “discrete” (separate) energy energy levelslevels for each atom that can only produce light of certain wavelengths (this is NOT ordinary white light!).

Increasing frequency (f) (increasing energy)

Increasing frequency (f) (increasing energy)

Hydrogen

Only certain energy levels can occur (not a continuous spectrum)

Energy Level Diagram

The larger the difference in energy, the greater the frequency (thus, the more purple the light).

Increasing potential energy

Frequency

Visible

convergence:convergence: the lines in a spectrum converge (get closer together) as frequency increases. related to how much energy is required

to remove the electron from the atom (ionize)

Closer to nucleus

Further from nucleus

Increasin

g frequ

ency

Stop

Electronic StructureElectronic Structure

Energy LevelsShells

Most stable = closest to nucleus

1st energy level = 2

2nd energy level = 8

Electronic structure: number of electrons in each orbital

H=1O=2,6 (two electrons in the first

energy level, six in the second)Al=2,8,3Cl=Ca=

Different isotopes have the same electronic structure and the same chemical properties!

Electron BehaviorElectron BehaviorValence shell: outer shell of an atom

determine the physical and chemical properties of an atom

Valence Shell

How many electrons in valence shell? Al Ne Li Ca

Stop here

HL TopicHL Topic

Electronic Structure of AtomsElectronic Structure of AtomsZumdahl2: p. 307-312

Electronic Structure

I. Energy levelsA. Sub-levels

1. Orbitala. Spin

Energy Levels

Major shells (layers) around the nucleus filled before higher levels are filled 1st: 2 electrons 2nd: 8 electrons 3rd: 8 electrons

Sub-levelsDifferent shapess – sphere

one orbitalp – figure eight

three orbitalsd –

five orbitalsf –

seven orbitals

p Sub-level

p sub-level has three orbitalspx, py, pz

d and f sub-levels have very complex shapes

Orbitals

Each orbital can hold two electrons.Electrons spin in opposite directions

Energy Level

Types of sub-

levels

Total orbits

Electron capacity

1 s 1 2

2 s, p 1+3=4

8

3 s, p, d 1+3+5=9

18

4 s, p, d, f 1+3+5+7=16

2

Energies of sub-levels

Electronic structure of atoms

Energy States

Depending on where an electron was around the nucleus, it had different energy states.

Ground state: An orbit near the nucleus: not very exited at all.

Excited State: An orbit farther awayfrom the nucleus: much morepotential for giving off energy.

Heisenberg Uncertainty Principle

If electrons are both waves and particles, where are they around the atom?

It is impossible to figure out both the position and velocity of an electron, at the same time.

We CAN figure out the probability that an electron is in any one spot at any given time.

Electron Configuration

The arrangement of electrons in an atom Each element’s atoms are different Arrangement with the lowest energy=

ground state electron configurationHow do we figure out what the

ground state electron configuration looks like?

How do we figure out where the electrons are?

1. Figure out the energy levels of the orbitals

2. Add electrons to the orbitals according to three rules

1: Aufbau Principle1: Aufbau Principle

An electron goes to the lowest-energy orbital that can take it.

2: Pauli Exclusion Principle

No two electrons can have exactly the same configuration description Can have the same orbital, but must

have opposite spins.

3. Hund’s RuleOrbitals of equal energy are each

occupied by one electron before any orbital is occupied by a second electron

All electrons that are by themselves in an orbit must have the same spin.

Electron configuration: the arrangement of electrons in an atom.

So…what do we do with this information?!

How do we write electron configurations?

Electron Configuration NotationOrbital NotationNoble Gas Notation (shorthand)

All ways to communicate where the electrons are in the ground state of any atom.

s – sphere one orbital – 2 electrons

p – figure eight three orbitals – 6 electrons

d – five orbitals – 10 electrons

f – seven orbitals – 14 electrons

Orbital Notation

Electron configuration goes below a line or box

Arrows representing electrons go on the lines or in the boxes

1s 2s 2p 3s 3p 4s

Fluorine? 9 electrons

Magnesium? 12 electrons1s 2s 2p 3s 3p 4s

1s 2s 2p 3s 3p 4s

Electron Configuration NotationMain energy level Sub-levelElectrons

Carbon (6 electrons) 1s22s22p2

Aluminum (13 electrons) 1s22s22p63s23p1

OxygenArgonCopper

Orbital Notation

Boron1s22s22p1

Atomic Number?How many electrons?Orbital notation

Aufbau Principle: start with 1s and work up in energy level

Pauli Exclusion Principle: No two elements can have the same arrangement of electrons

Hund’s Rule: Fill in one electron per orbital first, then go back.

Orbital Notation

Nitrogen1s22s22p3

Atomic Number?Number of Electrons?Orbital Notation?

Practice

Write the orbital notation for:FluorineAluminumCarbonOxygen

Practice

Write the electron configuration notation of:

Be (Beryllium)N (Nitrogen)Si (Silicon)Na (Sodium)

Noble Gas Notation (Shorthand)

Noble gasses have totally filled outer orbitals.

If Ne (a noble gas) is 1s22s22p6, we can abbreviate Na as [Ne]3s1.

Sodium has one more electron than Neon, so its Noble Gas Notation is Neon plus one electron in the s sublevel of the third energy level.

Practice

Fe Electron Configuration Notation Noble Gas Notation

K Electron Configuration Notation Noble Gas Notation

LiBe