The Structure of the Atom Chapter 5 Chemistry
Ch5 asgns. From book • 5.1&2: 163/28,29,30,33-36 • 5.4: 164/55,56,58,59,61,62 • Quiz and Test #1 after 5.1,.2,.4. • 5.3: 163/42-48,50,51,69-75 • Worksheets will also be assigned. • Test #2 after 5.3 is covered.
It started a long time ago… 460 – 370 BC Today Democritus Beginning of Atomism You cannot divide something in half forever. The smallest piece of matter is called an atom.
Dalton’s Postulates 1808 Today 460 – 370 BC 1.All elements are made of tiny indivisible particles called atoms. Democritus Atomism 2. All atoms of the same element are the same, but different from atoms of every other element. Over 2,000 years later John Dalton comes up with the first “modern” atomic theory. 3.Chemical reactions rearrange atoms but do not create, destroy, or convert atoms from one element to another. 4. Compounds are made from combining atoms in simple whole number ratios.
Another kind of light? Today 1870 460 – 370 BC 1808 Democritus Atomism Dalton “Modern” atomic theory William Crookes invents a tube in which virtually all the gas has been removed. Under high voltage, a ray was emitted from the cathode end of the tube.
It started a long time ago… 1897 Today 460 – 370 BC 1808 1870 Democritus Atomism Crookes Cathode rays Dalton “Modern” atomic theory J.J. Thomson discovers the electron Cathode rays must be negative.
It started a long time ago… 1910 Today 460 – 370 BC 1808 1897 1870 Democritus Atomism Crookes Cathode rays Thomson Discovery of the electron Dalton “Modern” atomic theory Ernest Rutherford discovers the nucleus
Size and mass The size of the atom comes mostly from the space occupied by the electrons The mass of the atom comes mostly from the nucleus
neutrons protons electrons What happens when you change the number of protons?
6 protons in carbon 7 protons in nitrogen 8 protons in oxygen You obtain a different element! The number of protons is also called the atomic number for that element.
neutrons protons electrons What happens when you change the number of electrons? You get an ion – a charged particle.
A neutral sodium atom Na 11 protons The protons and electrons cancel each other out Balanced charges A positive sodium ion Na1+ One proton is not neutralized by an electron, making this a +1 charged atom One electron short
8 protons A negative oxygen ion Two electrons are not neutralized by protons, making this a –2 charged atom O-2 Two extra electrons
The electron cloud Electrons are very light and fast. They are not organized along orbits around the nucleus. Except for mass, virtually every property of atoms is determined by electrons, including size and chemical bonding
neutrons protons electrons What happens when you change the number of neutrons?
Atomic number Neutrons act as “glue.” They hold protons together in the nucleus.
Mass number = 6 p + 6 n = 12 12C “carbon-12” mass number: total number of protons and neutrons in a nucleus.
Carbon-12 Carbon-13 Carbon-14 Name Mass number 12 13 14 6 6 6 # protons 6 7 8 # neutrons isotopes: atoms or elements that have the same number of protons in the nucleus but different number of neutrons
Number of neutrons for each of 100 lithium atoms randomly sampled from nature It’s an AVERAGE mass!
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.
Assignment: 5.1&2: 163/28,29,30,33-36 and handout(s)
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 verysmall 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 oflight (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.
On the scale of atoms Light Electrons 4.136x10-3 eV or or 4.136x10-3 eV Planck’s constant (h) is used to calculate the energy and wavelength of electrons and photons
l = h = √ 2mE l = 6.626x10-34Js √2(9.109x10-31kg)(6.636x10-20J l = 1.906 x 10-9 m
Energy of a photon Light travels as bundles called photons A very small unit of energy 1 electron volt (eV) = 1.602 x 10–19 J.
Wavelength and frequency are related 1 Hertz, Hz = 1 cycle = 1 = s-1 sec sec
What is the frequency of a yellow light with wavelength 580 nm? 1 nm = 10-9 m c = fl--> f = c l f = 3 x 10 8 m 580 x 10-9ms f = 5.2 x 1014 Hz
The wavelength of red laser light is 652 nm. What is its frequency, n? How much energy, E, does a photon of this light have in electron volts? 1 nm = 10-9m Asked:Frequency and energy Given: Relationships: Solve: Answer: Since 1 Hz = 1/s, the frequency is 4.6 x 1014 Hz and the energy is 1.9 eV.
Wave addition The sum of two waves can give a “bigger” wave.
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 Only certain energy levels are allowed Energy is quantized!
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.
A look at history 1925 Today 460 – 370 BC 1808 1897 1910 1870 Democritus Atomism Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Dalton “Modern” atomic theory Wolfgang Pauli Quantum rule on electron structure Pauli exclusion principle: two electrons in the same atom may never be in the same quantum state.
Lithium’s 3rd electron has to go into the 2nd energy level Fill lower-energy levels first One electron per quantum state
1st row Full energy level
Principle quantum number Quantum states Energy levels Orbitals s 1