CHAPTER 5 The Structure of the Atom 5.2 The Quantum Atom
Why is the periodic table shaped this way? We have seen in Chapter 2 that elements in the periodic table are organized by chemical properties.
Why is the periodic table shaped this way? 2 elements 8 elements 8 elements 18 elements Why is it not shaped like a “box”?
Elements in the same column have similar chemical properties. The periodic table Li+ Na+ K+ They tend to donate 1 electron.
Elements in the same column have similar chemical properties. The periodic table F– Cl– Br– They tend to accept 1 electron.
Elements in the same column have similar chemical properties. The periodic table Never in ionic form They do not donate or accept electrons.
Electrons are responsible for these chemical properties. Elements in the same column have similar chemical properties. Electrons are responsible for these chemical properties. Quantum theory explains how the universe behaves on a very small scale. Niels Bohr
A wave “particle” We intuitively think of light as a wave and an electron as a particle
A wave “particle” But light waves come in bundles of light (photons) and an electron behaves as a wave
frequency: the rate at which an oscillation repeats; one hertz (Hz) is a frequency of one oscillation per second. wavelength: the distance (separation) between any two successive peaks (or valleys) of a wave.
The higher the frequency, the higher the energy
On the scale of atoms Planck’s constant (h) is used to calculate Electrons Light Planck’s constant (h) is used to calculate the energy and wavelength of electrons and photons
The sum of two waves can give a “bigger” wave. Wave addition The sum of two waves can give a “bigger” wave.
The sum of two waves can be zero! Wave addition The sum of two waves can be zero!
Wave addition Imagine a wave (wave 1) inside a box… Wave 1 bounces off the wall and creates wave 2. Could the waves cancel out each other? Wave 1 Wave 2 Wave that “survives”
Perfect “fit” Poor “fit”
The wavelength of the electron must be a “multiple” of the “size” of the atom. Allowed Not allowed
Only certain wavelengths are allowed… … and wavelength is related to energy.
The Bohr model Energy is quantized! Only certain energy levels are allowed Energy is quantized!
Different quantum states can have the same wavelength The Bohr model Different quantum states can have the same wavelength
orbital: group of quantum states that have similar spatial shapes, labeled s, p, d, and f.
The orbital shapes are responsible for the shapes of molecules.
A look at history 460 – 370 BC 1808 1870 1897 1910 Today Democritus Atomism Dalton “Modern” atomic theory Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus
Wolfgang Pauli Quantum rule on electron structure A look at history 460 – 370 BC 1808 1870 1897 1910 1925 Today Democritus Atomism Dalton “Modern” atomic theory Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Wolfgang Pauli Quantum rule on electron structure Pauli exclusion principle: two electrons in the same atom may never be in the same quantum state.
Quantum states can have the same energy level
Lithium’s 3rd electron has to go into the 2nd energy level Fill lower-energy levels first One electron per quantum state
Electrons are arranged in a pattern according to energy levels. - Lower energy levels are filled first - There can only be one electron per quantum state Lithium’s 3rd electron has to go into the 2nd energy level Energy is quantized