1. Sci-101 Introduction to Physics
Chap Atomic Models
Dr. Alexander Dzyubenko
adzyubenko
© A.B. Dzyubenko 2003, 2004

2. Physical and Conceptual Models
Atoms cannot be seen through a microscope, because they are smaller than the wavelength of visible light

3. Physical and Conceptual Models, cont
Visible objects can be represented with a physical model, which replicates the object at a more convenient scale
A conceptual model is a representation of a system that helps in making predictions about how the system behaves

4. Identifying Atoms Using the Spectroscope
By passing white light through a prism, the color component of the light can be separated
A spectroscope is an instrument to observe the color components of any light source

5. Identifying Atoms Using the Spectroscope, cont
The atoms of the given element emit only certain frequencies of light
This pattern of distinct frequencies: that element’s atomic spectrum

6. The Quantum Hypothesis
Max Planck ( ) hypothesized that warm bodies emit radiant energy in discrete bundles, which he called quanta
The energy in each energy bundle is proportional to the frequency of radiation
Quantum mechanics – a new view of the physical world

7. The Quantum Hypothesis, cont
Albert Einstein ( ): light is quantized, which means it consists of a stream of energy packets
Each packet is called a quantum, also known as a photon

8. The Quantum Hypothesis,cont
Niels Bohr( ) explained the formation of atomic spectra

9. The Quantum Hypothesis
When an atom absorbs a photon of light, one of the electrons gains energy
When the atom emits a photon of light, the high-energy electron loses some of its energy

10. The Planetary Model of the Atom
Bohr: because light energy is quantized, the energy of an electron in an atom must also be quantized
There are only a limited number of permitted energy levels of electrons in an atom

11. The Planetary Model of the Atom
Each energy level has a principal quantum number n=1, 2, 3, …

12. The Planetary Model of the Atom, cont
The frequency of light emitted (or absorbed) by an atom is proportional to the energy difference between electron orbits

13. Electron Waves Louis de Broglie (1892-1987):
an electron has both wave properties and particle properties
Practical application: the electron microscope focuses electron waves instead of light waves
Has a better resolution

14. Figure A color-enhanced electron microscope photograph shows significant detail of a storage mite, Lepidoglyphus destructor. The mite is so small, with a maximum length of mm, that ordinary microscopes do not reveal minute anatomical details.
A color-enhanced electron microscope photograph shows significant detail of a storage mite, Lepidoglyphus destructor. The mite is so small, with a maximum length of 0.75 mm, that ordinary microscopes do not reveal minute anatomical details.

15. Probability Clouds and Atomic Orbitals
for hydrogen’s electron
The intensity of electron wave at any given location determines the probability to find the electron at that location
An atomic orbital specifies a volume of space where the electron is located most of the time

16. The Shell Model
Electrons behave as they are arranged in a series of concentric shells
There are at least seven shells and each shell can hold only a limited number of electrons
Energy shell: all energy levels with same
principal quantum number n =1, 2, 3, …

17. Shell Model and Periodic Table
A series of seven concentric shells accounts for the seven periods of the periodic table
The number of elements in each period is equal to the shell’s capacity for electrons
Three periods shown

18. Seven Shells and their capacities