Sci-101 Introduction to Physics Chap. 15 Atomic Models Dr. Alexander Dzyubenko http://www.csub.edu/~ adzyubenko © A.B. Dzyubenko 2003, 2004

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

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

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

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

The Quantum Hypothesis Max Planck (1858-1947) 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

The Quantum Hypothesis, cont Albert Einstein (1879-1955): light is quantized, which means it consists of a stream of energy packets Each packet is called a quantum, also known as a photon

The Quantum Hypothesis,cont Niels Bohr(1885-1962) explained the formation of atomic spectra

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

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

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

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

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

Figure 40.18 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. 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.

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

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, …

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

Seven Shells and their capacities