1. Ch. 4-1 Models of the Atom
Atomic Structure

2. POINT > Describe some basic properties of light
POINT > Describe the emission-line spectrum of hydrogen
POINT > Identify how Bohr explained electron orbitals
POINT > Describe how Bohr’s atomic model explained the emission-line spectrum of hydrogen

3. Models through Time…(so far)
Dalton

4. Models through Time…(so far)
Thomson

5. Models through Time…(so far)
Problem:
Could not explain
chemical
properties of
elements or locate electrons
Rutherford

6. WB CHECK:
Whose experiment demonstrated the existence of the atomic nucleus?
Whose experiment discovered the electron?
Whose experiment gave us the “plum pudding” model of the atom?

7. POINT > Describe some basic properties of light
Visible light is a small part of the energy range of the electromagnetic spectrum (a continuous spectrum)
Light has properties of both waves and particles

8. POINT > Describe some basic properties of light
Waves have frequency, v (cycles/second, or Hertz, Hz)
Waves have a wavelength, λ

9. POINT > Describe some basic properties of light
c = λ v
c is a constant (the speed of light), so frequency and wavelength are inversely related
Higher frequency = higher energy

10. WB CHECK:
As the wavelength of electromagnetic radiation decreases, what happens to the frequency?
As the wavelength of electromagnetic radiation decreases, what happens to the energy level?

11. Which has more energy, red light or blue light?
WB CHECK:
Which has more energy, red light or blue light?

12. POINT > Describe the emission-line spectrum of hydrogen
Light Bulb
Continuous Spectrum
Hydrogen Lamp
Not continuous

13. POINT > Describe the emission-line spectrum of hydrogen

14. POINT > Identify how Bohr explained electron orbitals
Niels Bohr (1885 – 1962)
Student of Rutherford
Proposed that electrons can only be found in specific paths (orbits) around the nucleus

15. POINT > Identify how Bohr explained electron orbitals
Niels Bohr used the emission spectrum of hydrogen to develop a quantum model for H atom
A quantum is a discrete, minimum amount of energy that an electron can absorb or emit
Central idea: Electrons can circle the nucleus only in certain, defined energy levels (orbitals)

16. The further from the nucleus, the higher the energy level (usually)
POINT > Describe how Bohr’s atomic model explained the emission-line spectrum of hydrogen
Each electron has a fixed energy called an energy level (like a rung on a ladder)
To move between levels, a quantum of energy must be absorbed or emitted
The further from the nucleus, the higher the energy level (usually)

17. POINT > Describe how Bohr’s atomic model explained the emission-line spectrum of hydrogen

18. WB CHECK:
The emission-line spectrum of hydrogen is discontinuous because
Electrons and protons have opposite charges
Electrons can absorb or emit a continuous range of energies
Electrons are fixed in orbitals that cannot change
Electrons can absorb or emit only discrete amounts of energy

19. WB CHECK:
As electrons move farther from the nucleus, do they have more or less energy?
What must happen for an electron to move from one orbital to a higher orbital?

20. POINT > Describe how Bohr’s atomic model explained the emission-line spectrum of hydrogen
Bohr’s model (1913)
Electrons orbit the nucleus in circular paths of fixed energy (energy levels)

21. Electrons absorb energy to go to an excited state
POINT > Describe how Bohr’s atomic model explained the emission-line spectrum of hydrogen
Again, a quantum is the amount of energy required to move an electron from one energy level to another
Electrons absorb energy to go to an excited state
Electrons emit energy to return to the ground state

22. Models through Time…(so far)
Problem: This
explained
hydrogen, but was inaccurate
with more than one electron
Bohr

23. Homework:
Read 4.1 pages 91-97
F.A. page 97 #1-6