* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 5
Elementary particle wikipedia , lookup
Chemical bond wikipedia , lookup
Bremsstrahlung wikipedia , lookup
Molecular Hamiltonian wikipedia , lookup
Double-slit experiment wikipedia , lookup
Particle in a box wikipedia , lookup
Molecular orbital wikipedia , lookup
Auger electron spectroscopy wikipedia , lookup
Rutherford backscattering spectrometry wikipedia , lookup
Hydrogen atom wikipedia , lookup
X-ray photoelectron spectroscopy wikipedia , lookup
Matter wave wikipedia , lookup
X-ray fluorescence wikipedia , lookup
Theoretical and experimental justification for the Schrödinger equation wikipedia , lookup
Atomic orbital wikipedia , lookup
Tight binding wikipedia , lookup
Wave–particle duality wikipedia , lookup
Chapters 4 & 5 Atomic Theory Section 4.3 Atomic Number • The key distinguishing trait between different elements is the number of protons in the nucleus. • The “atomic number” (Z) is the number of protons in an element • Consider tin (atomic symbol “Sn”). If a neutral tin atom contains 50 protons, how many electrons does it have? Mass Number • The total number of protons and neutrons in an atom is called the “mass number”. • The atomic number of gold (Au) is 79. If the mass number for gold is 197, how many neutrons does a typical gold atom contain? – a. 197 b. 79 c. 118 d. 122 Chemical Symbols • The complete symbol for an element on the Periodic Table includes the atomic symbol, the mass number, and the atomic number. Superscript → Subscript → Atomic number Mass number X • Note: you can also refer to atoms by using the mass number and the name of the element, i.e. gold-197. Comprehension Check • Identify the atomic number and mass number in the symbol for bromine below. Then, find the number of protons, neutrons and electrons in a typical bromine atom. 35 80 Br • Draw the complete chemical symbol for the element that has the atomic number 19. What is the name of this element? • A scientist has a mystery atom with 47 protons and 62 neutrons. What element is this? How is this atom unique? • Use your Periodic Table to answer these questions. Isotopes • Isotopes are atoms that have the same number of protons but different numbers of neutrons. – Whose theory of the atom does this contradict? • Health Science Application: Nuclear Medicine – Nanoparticles of gold-198 are used in some radiotherapy cancer treatments (particularly for prostate cancer). • Fun Fact: The only known stable (non-radioactive) isotope of gold is gold-197. • Note: Isotopes of the same element are chemically alike because they have the same number of protons and electrons. • Right now, we’re concerned with chemical reactions. Nuclear reactions come in Chapter 25! The Three Known Hydrogen Isotopes Atomic Mass • Recall, the number of protons plus the number of neutrons in an atom is the mass number. • The atomic mass of an element is the weighted average mass of all naturally occurring isotopes of that element. » Math Check: What is the difference between a weighted average and an arithmetic mean? – The weighted average reflects both the mass and the percent abundance of the isotopes. Measuring Atomic Mass • Scientists do not measure the mass of single atoms in grams. – The numbers would always be tiny and complicated • Mass of 1 proton = 1.673x10-24 grams • Instead of grams, we use atomic mass units based on the mass of a carbon-12 atom. – By definition 1 amu = 1/12 mass of carbon-12 atom. • Why carbon-12? – High isotope purity Isotopes of Carbon Carbon = 12.011 Calculating a Weighted Average • Naturally ocurring iron (Fe) has 4 isotopes: iron54 (5.845%), iron-56 (91.754%), iron-57 (2.119%), and iron-58 (0.282%). Find iron’s atomic mass by computing the weighted average of these four isotopes. • 54 x 5.845% = 3.156 • 56 x 91.754% = 51.382 • 57 x 2.119% = 1.208 • 58 x 0.282% = 0.164 • Total = 55.91 amu Preview of the Periodic Table • A periodic table is an arrangement of elements in which the elements are separated into groups based on a set of repeating properties. • The periodic table allows you to easily compare the properties of one element to another. • Each horizontal row is called a period. • Each vertical column is called a group, or family. – Elements in a group typically have similar physical and chemical properties Section 5.1 Atomic Orbitals • Principal Quantum Number (n) = the energy level of the electron: 1, 2, 3, etc. • These are called atomic orbitals (coined by scientists in 1932) - regions where there is a high probability of finding an electron. • Sublevels- like theater seats arranged in sections: letters s, p, d, and f Principal Quantum Number Generally symbolized by “n”, it denotes the shell (energy level) in which the electron is located. Maximum number of electrons that can fit in an energy level is: 2n2 # of shapes (orbitals) s 1 p 3 d 5 f 7 Summary Maximum electrons Starts at energy level 2 1 6 10 2 14 4 3 By Energy Level • • • • First Energy Level Has only s orbital only 2 electrons 1s2 • Second Energy Level • Has s and p orbitals available • 2 in s, 6 in p 2 6 • 2s 2p • 8 total electrons By Energy Level • Third energy level • Has s, p, and d orbitals • 2 in s, 6 in p, and 10 in d • 3s23p63d10 • 18 total electrons • Fourth energy level • Has s, p, d, and f orbitals • 2 in s, 6 in p, 10 in d, and 14 in f • 4s24p64d104f14 • 32 total electrons By Energy Level Any more than the • The orbitals do not fourth and not all fill up in a neat order. the orbitals will fill • The energy levels up. overlap • You simply run out of • Lowest energy fill electrons first. Section 5.2 Electron Arrangement in Atoms • OBJECTIVES: •Describe how to write the electron configuration for an atom. 7p 7s 6s 6p 5p 6d 5f 5d 4f 4d Increasing energy 5s 4p 3d 4s 3p 3s 2p 2s aufbau diagram - page 133 1s Aufbau is German for “building up” Electron Configurations… • …are the way electrons are arranged in various orbitals around the nuclei of atoms. Three rules tell us how: 1) Aufbau principle - electrons enter the lowest energy first. • This causes difficulties because of the overlap of orbitals of different energies – follow the diagram! 2) Pauli Exclusion Principle - at most 2 electrons per orbital - different spins Pauli Exclusion Principle No two electrons in an atom can have the same four quantum numbers. To show the different direction of spin, a pair in the same orbital is written as: Wolfgang Pauli Electron Configurations 3) Hund’s Rule- When electrons occupy orbitals of equal energy, they don’t pair up until they have to. • Let’s write the electron configuration for Phosphorus We need to account for all 15 electrons in phosphorus 7p 7s 6s 6p 5p 6d 5f 5d 4f 4d Increasing energy 5s 4p 3d 4s 3p 3s 2p 2s 1s • The first two electrons go into the 1s orbital Notice the opposite direction of the spins • only 13 more to go... 7p 7s 6s 6p 5p 6d 5f 5d 4f 4d Increasing energy 5s 4p 3d 4s 3p 3s 2p 2s 1s • The next electrons go into the 2s orbital • only 11 more... 7p 7s 6s 6p 5p 6d 5f 5d 4f 4d Increasing energy 5s 4p 3d 4s 3p 3s 2p 2s 1s • The next electrons go into the 2p orbital • only 5 more... 7p 7s 6s 6p 5p 6d 5f 5d 4f 4d Increasing energy 5s 4p 3d 4s 3p 3s 2p 2s 1s • The next electrons go into the 3s orbital • only 3 more... 7p 7s 6s 6p 5p 6d 5f 5d 4f 4d Increasing energy 5s 4p 3d 4s 3p 3s 2p 2s 1s Orbital notation • The last three electrons go into the 3p orbitals. They each go into separate shapes (Hund’s) • 3 unpaired electrons = 1s22s22p63s23p3 Orbitals fill in an order • Lowest energy to higher energy. • Adding electrons can change the energy of the orbital. Full orbitals are the absolute best situation. • However, half filled orbitals have a lower energy, and are next best •Makes them more stable. •Changes the filling order Section 5.3 Physics and the Quantum Mechanical Model • OBJECTIVES: •Describe the relationship between the wavelength and frequency of light. Section 5.3 Physics and the Quantum Mechanical Model • OBJECTIVES: •Identify the source of atomic emission spectra. Section 5.3 Physics and the Quantum Mechanical Model • OBJECTIVES: •Explain how the frequencies of emitted light are related to changes in electron energies. Light • The study of light led to the development of the quantum mechanical model. • Light is a kind of electromagnetic radiation. • Electromagnetic radiation includes many types: gamma rays, x-rays, radio waves… • Speed of light = 2.998 x 108 m/s, and is abbreviated “c” • All electromagnetic radiation travels at this same rate when measured in a vacuum - Page 139 “R O Y G B I V” Frequency Increases Wavelength Longer Parts of a wave Crest Wavelength Amplitude Origin Trough Electromagnetic radiation propagates through space as a wave moving at the speed of light. Equation: c = c = speed of light, a constant (2.998 x 108 m/s) (lambda) = wavelength, in meters (nu) = frequency, in units of hertz (hz or sec-1) Wavelength and Frequency • Are inversely related • As one goes up the other goes down. • Different frequencies of light are different colors of light. • There is a wide variety of frequencies • The whole range is called a spectrum - Page 140 Use Equation: c = Low Energy Radiowave s High Energy Microwave s Infrared . Low Frequency Ultraviolet X-Rays GammaRays High Frequency Long Wavelength Short Wavelength Visible Light Long Wavelength = Low Frequency = Low ENERGY Short Wavelength = High Frequency = High ENERGY Wavelength Table Atomic Spectra • White light is made up of all the colors of the visible spectrum. • Passing it through a prism separates it. If the light is not white • By heating a gas with electricity we can get it to give off colors. • Passing this light through a prism does something different. Atomic Spectrum • Each element gives off its own characteristic colors. • Can be used to identify the atom. • This is how we know what stars are made of. • These are called the atomic emission spectrum • Unique to each element, like fingerprints! • Very useful for identifying elements Light is a Particle? • • • • Energy is quantized. Light is a form of energy. Therefore, light must be quantized These smallest pieces of light are called photons. • Energy & frequency: directly related. The energy (E ) of electromagnetic radiation is directly proportional to the frequency () of the radiation. Equation: E = h E = Energy, in units of Joules (kg·m2/s2) (Joule is the metric unit of energy) h = Planck’s constant (6.626 x 10-34 J·s) = frequency, in units of hertz (hz, sec-1) The Math in Chapter 5 • There are 2 equations: 1) c = 2) E = h Know these! Explanation of atomic spectra • When we write electron configurations, we are writing the lowest energy. • The energy level, and where the electron starts from, is called it’s ground state the lowest energy level. Changing the energy • Let’s look at a hydrogen atom, with only one electron, and in the first energy level. Changing the energy • Heat, electricity, or light can move the electron up to different energy levels. The electron is now said to be “excited” Changing the energy • As the electron falls back to the ground state, it gives the energy back as light Changing the energy • They may fall down in specific steps • Each step has a different energy What is light? • Light is a particle – it contains discrete photons (it comes in chunks) • Light is a wave - we can measure its wavelength and it behaves as a wave • If we combine E=mc2 , c=, E = 1/2 mv2 and E = h, then we can get: = h/mv (from Louis de Broglie) • called de Broglie’s equation • Calculates the wavelength of a particle. The physics of the very small • Quantum mechanics explains how very small particles behave •Quantum mechanics is an explanation for subatomic particles and atoms as waves • Classical mechanics describes the motions of bodies much larger than atoms Wave-Particle Duality J.J. Thomson won the Nobel prize for describing the electron as a particle. His son, George Thomson won the Nobel prize for describing the wave-like nature of the electron. The electron is a particle! The electron is an energy wave! First paradox! • Light exists and acts as both a particle and a wave • Each nature of light can be measured and observed • Light is both at the same time!!! Heisenberg Uncertainty Principle • It is impossible to know exactly the location and velocity of a particle simultaneously. • The better we know one, the less we know the other. • Measuring changes the properties. • True in quantum mechanics, but not classical mechanics Heisenberg Uncertainty Principle “One cannot simultaneously determine both the position and momentum of an electron.” You can find out where the electron is, but not where it is going. Werner Heisenberg OR… You can find out where the electron is going, but not where it is! It is more obvious with the very small objects • To measure where a electron is, we use light. • But the light energy moves the electron • And hitting the electron changes the frequency of the light. After Before Photon wavelength changes Photon Moving Electron Electron velocity changes Fig. 5.16, p. 145 Second Paradox!!! • It is impossible to measure both the velocity and position of an electron at the same time. • It is only possible to measure or observe one or the other • Heisenberg Uncertainty Principle • Science is cray!!! Erwin Schrödinger and his cat • Austrian Physicist (1887-1961) • Challenged the paradox of the particle/wave duality • Created famous thought experiment about a cat in a box Schrödinger’s Cat Your assignment!! • Work within your table groups • Develop a model that could be used to explain the Heisenberg Uncertainty Principle to a student who is unfamiliar with quantum physics. • Assume the student is familiar with atomic structure • You can include objects that we don’t actually have (like ping pong balls or string or… BE CREATIVE!!) • You will describe the activity, including the materials needed • You will explain how the activity demonstrates the Heisenberg Uncertainty Principle, as well as a summary of the principle itself.