CHEMISTRYNovember 5, 2014

Electron Spectrum

SCIENCE STARTER

• You have 5 minutes. You are seated and quiet

• Do the Science Starter• The Science Starter will be

graded during class.

Question 1

• The electron cloud is divided into regions called principal energy levels/shells. Based on the picture above, circle the best answer for the following prompt: What is the lowest energy level?a. I Energy Levelb. II Energy Levelc. III Energy Leveld. IV Energy Level

Question 2

• The first energy level can hold up to 2 electrons. How many electrons can the 3rd energy level hold?

Question 3

• The distribution of the electrons among the shells (energy levels) is called the electron configuration. The electron configuration can be found on the periodic table. a. For an element, where on the period table is the

electron configuration located? b. What is the electron configuration for the

element carbon (C)?

Question 4

• The electron configuration provides the following information: the number of shells (energy levels) and the number of electrons in each shell.a. How many shells does the element carbon have?b. How many electrons is in the first shell? c. How many electrons is in the 2nd shell?

OBJECTIVES

• When an electron in an atom gains a specific amount of energy, the electron is at a higher energy state (excited state). (3.1j)

• When an electron returns from a higher energy state to a lower energy state, a specific amount of energy is emitted. This emitted energy can be used to identify an element. (3.1k)

AIM

• What makes the colors seen in fireworks?

EVIDENCE BASED TEMPLATE

• ON YOUR EVIDENCE BASED TEMPLATE, WRITE DOWN THE AIM AS THE GUIDED QUESTION

• What makes the colors seen in fireworks?• During the video, you will need to come up

with the following 2 things:– Claim– 2 evidence to support the claim

CLAIM

• Claim sentence starter:• The color as seen in fireworks is

caused by ___________________

FIREWORK COLOR

• The color as seen in fireworks is caused by HEATING a mixture of metal salts and metal oxides which react to produce an array of colors.

COMMON METAL SALTS

• Metal salts that are commonly used in firework displays include: strontium carbonate (red fireworks), calcium chloride (orange fireworks), sodium nitrate (yellow fireworks), barium chloride (green fireworks) and copper chloride (blue fireworks). Purple fireworks are typically produced by use of a mixture of strontium (red) and copper (blue) compounds.

SODIUM

• Two TYPES OF PHOTONS! • Both are yellow with different wavelengths•

Sodium Emission Lines

400 500 600 700

Wavelength in nanometers

COPPER

– Eight different types of photons.

– A purple one, a blue one, and several wavelengths of greens and yellows.

BRIGHTLINE SPECTRUM• The individual

photon colors emitted by the electrons in any atom form the “atomic emission spectrum”

• Also called “brightline spectrum”

ORDER OF COLORS

• red, orange, yellow, green, blue, indigo, violet• Red has the longest wavelength and the

lowest energy.• Violet has the shortest wavelength and the

highest energy.

SCIENCE BEHIND

• Heating up metal salts and metal oxides which react to produce an array of colors.

• Atoms absorb the energy causing its electrons to move from from their lowest energy state to a higher excited state.

• As the electrons fall down to a lower energy state, the excess energy gets emitted as light.

• Each element releases a different amount of energy and this energy is what determines the color or wavelength of the light that is emitted.

BRIGHT LINE SPECTRUM

• Compounds and metallic ions produce characteristic colors when placed in a flame. When these “flame tests” are passed through a prism, a bright line spectrum (black background with colored slits) can be seen.

BRIGHT LINE SPECTRUM (CONT’)

• A spectrum is produced when radiation from light sources is separated into different wavelength components.

• The bright line spectrum contains radiation of only specific wavelengths of light.

ATOMIC SPECTRA

• Continuous Spectrum – If white light is passed through a prism, a continuous spectrum (rainbow) can be observed.

SPECTRAL LINES

• Spectral lines are the fingerprints of the elements!

GROUND STATE VS EXCITED STATE

• The lowest energy state of an electron is called “ground state.”

• When an electron is in a higher energy state, it is called “excited state.”

GROUND STATE

• An electron in its lowest possible energy level• Each electron energy level contains the

maximum number of electrons that it can hold.

EXCITED STATE

• An electron that has gained energy and moved to a higher energy level – it’s very unstable!

• Example: 12Mg – Ground State:

• 2 – 8 – 2

– Excited state e- configuration:• 1 – 8 – 3 • 2 – 7 – 3 • 2 – 6 – 4

PHOTONS• If a photon of light strikes an atom, the energy in

the light may be transferred to the lower energy electrons (the energy is absorbed by the electron)

• This puts the electrons into an excited state causing the electron to moves to a higher energy level.

• This is an unstable situation.• The excited electron loses the extra energy (emits

energy) and fall back to the lower energy level.

BRIGHTLINE SPECTRUM

When only certain photons are observed, it means that only light packets of a particular type are being emitted!• Each photon has a specific energy value.• So only certain energy exchanges are

happening within the heated substance.• So there must only be certain ways of

changing the energy in the substance!

EMISSION

• Atoms have “layers” of electrons called energy levels.

• Each energy level has electrons with a certain amount of energy in them that matches the level.

• When the electrons change levels, they have to gain or lose energy to do so.

• Each time they lose energy, they emit a bundle of energy.

• We see that bundle as a photon!

QUANTUM

• A specific quantity of light

• Bohr said that when energy is added to atoms, the electrons gain a “quantum” of energy to move to a higher level.

• When electrons relax back to their normal state, they emit a quantum of energy to go back to the lowest level.

PHOTON• Photon is just the name for a quantum of light

• Electron Transition – when an electron moves from one level to another

– When an electron transitions to a higher energy level, a photon is absorbed.

– When an electron transitions to a lower energy level, a photon is emitted.

PHOTON

• The emitted photon is just a “piece” of light.• It has a specific energy value, so it has a

specific wavelength, frequency and color

• If you can measure the wavelength of the photon, you can calculate its energy.

CONCLUSION

• Atom of each elements emits unique photons of specific energies