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Atomic Structure Atoms and their structure History of the atom Not the history of atom, but the history of the idea of the atom Original idea Ancient Greece (400 B.C..) Democritus and Leucippus - two Greek philosophers History of Atom Looked at beach Made of sand Cut sand - smaller sand Smallest possible piece? Atomos - not to be cut Another Greek Aristotle - Famous philosopher All substances are made of 4 elements Fire - hot Air - light Earth - cool, heavy Water - wet Blend these in different proportions to get all substances Who Was Right? Greek society was slave based It was beneath the famous to work with their hands They did not experiment Greeks settled disagreements by argument Aristotle was more famous He won His ideas carried through to the middle ages. Alchemists therefore tried to change lead to gold Who’s Next? Late 1700’s - John Dalton - a famous English chemist conducted experiments Summarized results of his experiments and those of other’s Where? In Dalton’s Atomic Theory Combined ideas of elements with that of atoms Dalton’s Atomic Theory All matter is made of tiny indivisible particles called atoms. Atoms of the same element are identical, those of different atoms are different. Atoms of different elements combine in whole number ratios to form compounds Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed. Law of Definite Proportions Each compound has a specific ratio of elements It is a ratio by mass Water is always 8 grams of oxygen for each gram of hydrogen Law of Multiple Proportions If two elements form more that one compound, the ratio of the second element that combines with 1 gram of the first element in each is always a simple whole number. Parts of Atoms J. J. Thomson - English physicist. 1897 Made a piece of equipment called a cathode ray tube. It is a vacuum tube - all the air has been pumped out. Thomson’s Experiment Voltage source - + Vacuum tube Metal Disks Thomson’s Experiment Voltage source - + Thomson’s Experiment Voltage source - + Thomson’s Experiment Voltage source - + Thomson’s Experiment Voltage source + Passing an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source + Passing an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source + Passing an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source + Passing an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field he found that the moving pieces were negative J. J. Thomsom’s Model Discovered the electron Couldn’t find positive (for a while) Said the atom was like plum pudding A bunch of positive stuff, with the electrons able to be removed Other pieces Proton - positively charged pieces 1840 times heavier than the electron Neutron - no charge but the same mass as a proton. Where are the pieces? Rutherford’s experiment Ernest Rutherford - another famous English physicist. (1910) He believed in the plum pudding model of the atom. He wanted to see how big the electrons (plums) were. Used radioactive Uranium. Alpha particles - positively charged pieces given off by uranium 2He4 Shot them at gold foil which can be made a few atoms thick Rutherford’s experiment When the alpha particles hit a florescent screen, it glows. Here’s what the set up of the experiment looked like. Lead block Uranium Florescent Screen Gold Foil He Expected The alpha particles to pass through without changing direction very much Because – The positive charges were spread out evenly. Alone they were not enough to stop the alpha particles What he expected Because Because, he thought the mass was evenly distributed in the atom Because, he thought the mass was evenly distributed in the atom What he got Conclusions of Rutherford's Experiment: 1. Atom is mostly empty Because most particles passed straight through 2. Small dense, positive piece at center Because Alpha particles are deflected by the nucleus it if they get close enough + + Bohr Model Planetary Model or Heliocentric Model Places the nucleus in the center of the atom like the sun in the center of the universe Places the electrons in orbitals revolving around the nucleus, like the planets revolve around the sun. (fixed paths) Modern View The atom is mostly empty space Two regions – Nucleus: » protons and neutrons – Electron cloud: » region where you might find an electron based on mathematical probability. Density and the Atom Since most of the particles went through, it was mostly empty. Because the pieces turned so much, the positive pieces were heavy. Small volume, big mass, big density This small dense positive area is the nucleus Scale: marble in a football field. Subatomic particles Relative Actual mass (g) Name Symbol Charge mass Electron e- -1 1/1840 9.11 x 10-28 Proton p+ +1 1 1.67 x 10-24 Neutron n0 0 1 1.67 x 10-24 Structure of the Atom There are two regions – The nucleus » With protons and neutrons » Positive charge » Almost all the mass – Electron cloud- Most of the volume of an atom » The region where the electron can be found Size of an atom Atoms are small. Measured in picometers, 10-12 meters Hydrogen atom, 32 pm radius Nucleus tiny compared to atom (marble in a football field) Radius of the nucleus near 10-15m. Counting the Pieces Atomic Number = number of protons – # of protons determines kind of atom – The # of protons is the same as the number of electrons in a neutral atom Mass Number = the number of protons + neutrons End of Part One Atomic Structure - Part Two Symbols Contain the symbol of the element, the mass number and the atomic number Symbols Contain the symbol of the element, the mass number and the atomic number Mass number Atomic number X Symbols Find the – number of protons – number of neutrons – number of electrons – Atomic number – Mass Number 19 9 F Symbols Find the –number of protons –number of neutrons –number of electrons –Atomic number –Mass Number 80 35 Br Symbols if an element has an atomic number of 34 and a mass number of 78 what is the –number of protons –number of neutrons –number of electrons –Complete symbol Se Symbols if an element has 91 protons and 140 neutrons what is the –Atomic number –Mass number –number of electrons –Complete symbol Pa Symbols if an element has 78 electrons and 117 neutrons what is the –Atomic number –Mass number –number of protons –Complete symbol Pt Naming Isotopes Put the mass number after the name of the element carbon- 12 carbon -14 uranium-235 Isotopes Dalton was wrong. Atoms of the same element can have different numbers of neutrons Different mass numbers Called isotopes (do not confuse with allotropes) Atomic Mass How heavy is an atom of oxygen? – There are different kinds of oxygen atoms. – More concerned with average atomic mass. – Weighted average based on the abundances of all the naturally occurring isotopes in nature. – Don’t use grams because the numbers would be too small. Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) – AMU is based on the C-12 atom. It is one twelfth the mass of a carbon-12 atom. – Each isotope has its own atomic mass we need the average from percent abundance. It all averages out Test 1 2 3 4 5 6 Avg. Grade Student A 95 74 95 95 74 95 Student B 89 88 88 87 88 88 Test 6 Counts 50% Student A 95 x 10% = 74 x 10% = 95 x 10% = 95 x 10% = 74 x 10% = 95 x 50% = StudentA B Student 9589x x.110% = = 7488x x.110% = = 9588x x.110% = = 95 x .1 = 87 x 10% = 74 x .1 = 88 x 10% = 95 x .5 = = __________ 88 x 50%__________ __________ Atomic Mass Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass of 64.93 amu. Atomic Mass Magnesium has three isotopes. 78.99% magnesium 24 with a mass of 23.9850 amu, 10.00% magnesium 25 with a mass of 24.9858 amu, and the rest magnesium 26 with a mass of 25.9826 amu. What is the atomic mass of magnesium? If not told otherwise, the mass of the isotope is the mass number in amu Atomic Mass Is not a whole number because it is an average. The decimal numbers on the periodic table are based on the weighted average of all the known naturally occurring isotopes. The End Bohr’s Model Nucleus Electron Orbit Energy Levels Bohr’s Model Nucleus Electron Orbit Energy Levels Bohr’s Model Increasing energy Fifth Fourth Third Second First Nucleus Further away from the nucleus means more energy. There is no “in between” energy Energy Levels The Quantum Mechanical Model Energy is quantized. It comes in chunks. Quanta - the amount of energy needed to move from one energy level to another. Quantum leap in energy. Schrödinger derived an equation that described the energy and position of the electrons in an atom Treated electrons as waves The Quantum Mechanical Model a mathematical solution It is not like anything you can see. The Quantum Mechanical Model Does have energy levels for electrons. Orbits are not circular. It can only tell us the probability of finding an electron a certain distance from the nucleus. The Quantum Mechanical Model The electron is found inside a blurry “electron cloud” An area where there is a chance of finding an electron. Draw a line at 90 % Atomic Orbitals Principal Quantum Number (n) = the energy level of the electron. Within each energy level the complex math of Schrödinger's equation describes several shapes. These are called atomic orbitals. – To calculate number of orbitals : n2 – To calculate maximum electrons per energy level: 2n2 Regions where there is a high probability of finding an electron. S orbitals 1 s orbital for every energy level Spherical shaped Each s orbital can hold 2 electrons Called the 1s, 2s, 3s, etc.. orbitals. P orbitals Start at the second energy level 3 different directions 3 different shapes (dumbell) Each can hold 2 electrons P Orbitals D orbitals Start at the third energy level 5 different shapes Each can hold 2 electrons F orbitals Start at the fourth energy level Have seven different shapes 2 electrons per shape F orbitals Images J mol Summary # of shapes Max electrons Starts at energy level s 1 2 1 p 3 6 2 d 5 10 3 f 7 14 4 Filling order Lowest energy fill first. The energy levels overlap The orbitals do not fill up order of energy level. Counting system – Each box is an orbital shape – Room for two electrons Increasing energy 7s 6s 5s 7p 6p 6d 5p 5d 4s 4p 4d 3s 3p 3d 2s 2p 1s 5f 4f Increasing energy 7s 6s 5s 7p 6p 5p 4p 4s 3p 3s 2p 2s 1s 6d 5d 4d 3d 5f 4f Electron Configurations Aufbrau principle- electrons enter the lowest energy first. Pauli Exclusion Principle- at most 2 electrons per orbital - different spins Heisenberg’s Principle- we do not know the precise location of an electron only a probability of where the electron is in the orbital cloud. Electron Configuration Hund’s Rule- When electrons occupy orbitals of equal energy they don’t pair up until they have to . (up, up, up, then down, down, down.) Phosphorus electron config. Increasing energy 7s 6s 5s 7p 6p 6d 5d 5p 4d 4p 3d 4s 3p 3s 2s 1s The first to electrons go into the 1s orbital 2p Notice the opposite spins only 13 more 5f 4f Increasing energy 7s 6s 5s 7p 6p 6d 5d 5p 4d 4p 3d 4s 3p 3s 2s 1s The next electrons go into the 2s orbital 2p only 11 more 5f 4f Increasing energy 7s 6s 5s 4s 3s 2s 1s 7p 6p 5p 4p 6d 5d 4d 3d 3p • The next electrons go into the 2p orbital 2p • only 5 more 5f 4f Increasing energy 7s 6s 5s 4s 3s 2s 1s 7p 6p 5p 4p 6d 5d 4d 3d 3p • The next electrons go into the 3s orbital 2p • only 3 more 5f 4f Increasing energy 7s 6s 5s 4s 7p 6p 6d 5d 5p 4d 4p 3p • 3s 2s 1s 2p • • • 5f 4f 3d The last three electrons go into the 3p orbitals. They each go into separate shapes 3 unpaired electrons 1s22s22p63s23p3 The easy way to remember 7s 7p 7d 7f 6s 6p 6d 6f 5s 5p 5d 5f 4s 4p 4d 4f 3s 3p 3d 2s 2p 1s • 2 1s • 2 electrons Fill from the bottom up following the arrows 7s 7p 7d 7f 6s 6p 6d 6f 5s 5p 5d 5f 4s 4p 4d 4f 3s 3p 3d 2s 2p 1s • 2 2 1s 2s • 4 electrons Fill from the bottom up following the arrows 7s 7p 7d 7f 6s 6p 6d 6f 5s 5p 5d 5f 4s 4p 4d 4f 3s 3p 3d 2s 2p 1s • 2 2 6 2 1s 2s 2p 3s • 12 electrons Fill from the bottom up following the arrows 7s 7p 7d 7f 6s 6p 6d 6f 5s 5p 5d 5f 4s 4p 4d 4f 3s 3p 3d 2s 2p 1s • 2 2 6 2 1s 2s 2p 3s 6 2 3p 4s • 20 electrons Fill from the bottom up following the arrows 7s 7p 7d 7f 6s 6p 6d 6f 5s 5p 5d 5f 4s 4p 4d 4f 3s 3p 3d 2s 2p 1s • 2 2 6 2 1s 2s 2p 3s 6 2 10 6 3p 4s 3d 4p 5s2 • 38 electrons Fill from the bottom up following the arrows 7s 7p 7d 7f 6s 6p 6d 6f 5s 5p 5d 5f 4s 4p 4d 4f 3s 3p 3d 2s 2p 1s • 2 2 6 2 1s 2s 2p 3s 6 2 10 6 3p 4s 3d 4p 5s2 4d10 5p6 6s2 • 56 electrons Fill from the bottom up following the arrows 7s 7p 7d 7f 6s 6p 6d 6f 5s 5p 5d 5f 4s 4p 4d 4f 3s 3p 3d 2s 2p 1s • 2 2 6 2 1s 2s 2p 3s 6 2 10 6 3p 4s 3d 4p 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 • 88 electrons Fill from the bottom up following the arrows 7s 7p 7d 7f 6s 6p 6d 6f 5s 5p 5d 5f 4s 4p 4d 4f 3s 3p 3d 2s 2p 1s • 2 2 6 2 1s 2s 2p 3s 6 2 10 6 3p 4s 3d 4p 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6 • 118 electrons Rewrite when done • 2 2 6 2 6 2 10 6 2 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6 Group the energy levels together • 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d105f146s2 6p6 6d10 7s2 6 7p The Modern Table Elements are still grouped by properties Similar properties are in the same column Order is in increasing atomic number Added a column of elements Mendeleev didn’t know about. The noble gases weren’t found because they didn’t react with anything. Horizontal rows are called periods or principal energy levels. There are 7 periods Vertical columns are called groups. Elements are placed in columns by similar properties. Also called families 1A 2A The elements in the A groups 8A 0 are called the representative 3A 4A 5A 6A 7A elements Representative Elements Groups IA-VIIIA S and p Block Obey the octet rule VIIIA VIIA VIA IIIA IIB 13 14 15 16 17 3A 4A 5A 6A 7A IB VIIIB VIIB VIB VA IVB IIIB 1 2 1A 2A VA IIA IA IUPAC System for 1-18 (International Union of Pure and Applied Chemistry) IVA CAS System for A and B (Chemical Abstract Service) Other Systems 3 4 5 6 7 8 9 10 11 12 3B 4B 5B 6B 7B 8B 8B 8B 1B 2B 18 8A Metals Metals Luster – shiny. Ductile – drawn into wires. Malleable – hammered into sheets. Conductors of heat and electricity. Why? Sea of “mobile” electrons. Transition metals The Group B elements Dull Brittle Nonconductors - insulators Non-metals Metalloids or Semimetals Properties of both Semiconductors These are called the inner transition elements and they belong here Group 1A are the alkali metals Group 2A are the alkaline earth metals Group 7A is called the Halogens Group 8A are the noble gases Why? The part of the atom another atom sees is the electron cloud. More importantly the outside orbitals The orbitals fill up in a regular pattern The outside orbital electron configuration repeats So.. the properties of atoms repeat. H Li 1 3 Na 11 K 19 Rb 37 Cs 55 Fr 87 1s1 1s22s1 1s22s22p63s1 1s22s22p63s23p64s1 1s22s22p63s23p63d104s24p65s1 1s22s22p63s23p63d104s24p64d105s2 5p66s1 1s22s22p63s23p63d104s24p64d104f145s2 5p65d106s26p67s1 1s2 He 2 Ne 2 2 6 1s 2s 2p 10 1s22s22p63s23p6 Ar18 1s22s22p63s23p63d104s24p6 Kr 36 1s22s22p63s23p63d104s24p64d105s25p6 Xe 54 1s22s22p63s23p63d104s24p64d105s24f14 Rn 5p65d106s26p6 86 S- block s1 s2 Alkali metals all end in s1 Alkaline earth metals all end in s2 really have to include He but it fits better later He has the properties of the noble gases Transition Metals -d block s1 d5 d1 d2 d3 d5 d6 d7 d8 s1 d9 d10 The P-block p1 p2 p3 p4 p5 p6 F - block inner transition elements f1 f2 f3 f4 f5 f6 f7 f8 f9 f10 f11 f12 f13 f14 1 2 3 4 5 6 7 Each row (or period) is the energy level for s and p orbitals d orbitals fill up after previous energy level so first d is 3d even though it’s in row 4 1 2 3 4 5 6 7 3d 1 2 3 4 5 6 7 4f 5f f orbitals start filling at 4f Writing Electron configurations the easy way Yes there is a shorthand Electron Configurations repeat The shape of the periodic table is a representation of this repetition. When we get to the end of the row the outermost energy level is full. This is the basis for our shorthand The Shorthand Write the symbol of the noble gas before the element in brackets [ ] Then the rest of the electrons. Aluminum - full configuration 1s22s22p63s23p1 Ne is 1s22s22p6 so Al is [Ne] 3s23p1 More examples Ge = 1s22s22p63s23p63d104s24p2 2 10 2 Ge = [Ar] 4s 3d 4p Ge = [Ar] 3d104s24p2 Hf=1s22s22p63s23p64s23d104p64f14 4d105s25p65d26s2 Hf=[Xe]6s24f145d2 Hf=[Xe]4f145d26s2 The Shorthand Sn- 50 electrons The noble gas before it is Kr Takes care of 36 Next 5s2 Then 4d10 Finally 5p2 [ Kr ] 5s2 4d10 5p2 Electron configurations and groups Representative elements have s and p orbitals as last filled – Group number = number of electrons in highest energy level Transition metals- d orbitals Inner transition- f orbitals Noble gases s and p orbitals full