Chapter 5 Notes

Atomic Theory

Look at the photographs on the next pages and tell me how they

are all similar?

What do the photos have in common?

• They all are practical applications of Atomic Emission by Excited Electrons!• It’s this principle that helped

Bohr formulate his model of the atom.

Atomic Emission: How It Works

1. Normally, electrons are in the lowest energy levels (closest to the nucleus) called the ground state,

2. Electrons can absorb energy. The energy can be heat energy (a fire), or chemical energy (battery), or electrical energy (an outlet).

3. When an electron absorbs energy, it "jumps" to a higher energy level, and spins in the higher energy level called the excited state.

4. When the electron ‘falls’ back to the lower energy level, it emits (gives off) energy of specific wavelengths (lines) of LIGHT!

5. When the light is looked at through a prism or diffraction grating, bands of colored light can be seen called Bright-Line Spectra or simply Line Spectra.

6. Each element’s spectra is unique and can be used to identify it just like your fingerprints identify you!

Ground vs Excited State Notes

Ground State = electron in lowest energy state

Excited State = electron in higher energy state

Ground State Excited State

Ground State Excited State

Line Spectra – Unique bands of color emitted when excited electrons return to the ground state.

Electron GAINS energy & jumps to a higher energy level

Electron EMITS light energy & falls to a lower energy level

Bohr Model of Hydrogen

Backgound Only(Don’t copy to notes)

• Hot objects give off light. • When the light from a light bulb passes through

a prism, a RAINBOW or CONTINUOUS SPECTRUM forms.

• Remember ROY G. BIV?Red, Orange, Yellow, Green, Blue, Indigo, Violet

•

When the light from an element gas tube passes through a prism, only some colors are seen – called a BRIGHT-LINE SPECTRUM.

Gas Tube Power Supply Hydrogen gas gives off pink light

Hydrogen’s Bright Line Spectrum as viewed through a prism

Each element’s Line Spectra is unique.

Often Shown This Way

This site shows the Line Spectra of Various Elementshttp://jersey.uoregon.edu/elements/Elements.html

Repeat

White light forms a Continuous Spectrum (Rainbow).

Each element has unique spectra that can be used to identify it – Bright-Line Spectra or Line Spectra or Emission Lines.

Flame TestsCopper Sodium Potassium

Electron Configuration & Bohr ModelsHow to tell if its for the Ground or Excited state?

For Ground State1) Periodic Table is for ground state.2) The maximum # of electrons that can fill each

successive shell is 2, 8, 18, 32 (2n2).3) Fill one shell before filling the next.4) Some exceptions: So count up electrons to

figure out the atomic number and see if its on the PT. If NOT on PT, it’s excited state.

Practice: Excited or Ground

1) 2 – 3

2) 2 – 8 – 6 – 1

3) 2 – 8 – 8 – 2

4) 2 – 8 – 14 – 2

5) 2 – 8 – 2 – 1

Bohr Model for Boron

Ground State 10.81 +3 Excited State

5 B

5 p+6 no

5 p+6 no

2- 3

Electron Configuration 2-3 Electron Configuration 2 - 2 -1

Bohr Model for Phosphorus

Ground State 30.97 -3 Excited State

15 P

2-8-5

Do you know:

• Difference between excited and ground state?• How atoms become excited?• How atoms return to ground state?• Why spectra lines are important?• Ground or excited state? 2 – 5 – 1 Why?

Demonstration

• Put on Rainbow Glasses• Observe classroom lights & windows to see

Continuous Spectra.• Observe gas tubes to see unique Spectra

Lines.