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Unformatted text preview: Chapter 4 Chapter Atoms and their structure History of the atom History
Not the history of atom, but the idea of the Not atom. atom. s Original idea Ancient Greece (400 B.C.) s Democritus and Leucippus- Greek Democritus philosophers. philosophers.
s Looked at beach sSmallest possible Smallest s Made of sand piece? piece? s Cut sand - smaller sAtomos - not to be cut Cut sand sand
s History of Atom History Another Greek Another
Aristotle - Famous philosopher s All substances are made of 4 elements s Fire - Hot s Air - light s Earth - cool, heavy s Water - wet s Blend these in different proportions to Blend get all substances
s Did not experiment. s Greeks settled disagreements by Greeks argument. argument. s Aristotle was a better debater - He won. s His ideas carried through middle ages. s Alchemists tried to change lead to gold.
s Who Was Right? Who Who’s Next? Who’s
Late 1700’s - John Dalton- England. s Teacher- summarized results of his Teacherexperiments and those of others. experiments s Elements substances that can’t be Elements broken down broken s In Dalton’s Atomic Theory s Combined idea of elements with that of Combined atoms. atoms.
s 1 All matter is made of tiny indivisible All matter indivisible Dalton’s Atomic Theory Dalton’s particles called atoms. particles 2 Atoms of the same element are identical, Atoms those of different atoms are different. those 3 Atoms of different elements combine in Atoms whole number ratios to form compounds. whole 4 Chemical reactions involve the Chemical rearrangement of atoms. No new atoms are created or destroyed. are Law of Definite Proportions (#3) Law
Each compound has a specific ratio of Each elements. elements. s It is a ratio by mass. s Water is always 8 grams of oxygen for Water each gram of hydrogen.
s Law of Multiple Proportions Law
If two elements form more than one If compound, the ratio of the second element that combines with 1 gram of the first element in each, is a simple whole number. whole s The ratio of the ratios is a whole The number. number.
s What? What?
Water is 8 grams of oxygen per gram of Water hydrogen. hydrogen. s Hydrogen peroxide is 16 grams of Hydrogen oxygen per gram of hydrogen. oxygen s 16 to 8 is a 2 to 1 ratio. s True because you have to add a whole True atom, you can’t add a piece of an atom. atom,
s Parts of Atoms Parts
J. J. Thomson - English physicist. 1897 s Made a piece of equipment called a Made cathode ray tube. cathode s It is a vacuum tube - all the air has been It pumped out. pumped s A limited amount of other gases are put limited in in
s Thomson’s Experiment Thomson’s - Voltage source + Metal Disks Thomson’s Experiment s Voltage source + Passing an electric current makes a beam Passing appear to move from the negative to the positive end positive Thomson’s Experiment
Voltage source + s By adding an electric field By Thomson’s Experiment
Voltage source + s By adding an electric field he found that the By moving pieces were negative Thomson’s Experiment Thomson’s
Used many different metals and gases s Beam was always the same s By the amount it bent he could find the By ratio of charge to mass ratio s Was the same with every material s Same type of piece in every kind of Same atom atom
s Thomsom’s Model Thomsom’s
Found the electron. s Couldn’t find Couldn’t positive (for a while). positive s Said the atom was Said like plum pudding. like s A bunch of positive bunch stuff, with the electrons able to be removed. removed.
s Millikan’s Experiment Millikan’s
Atomizer + Oil Microscope Metal Plates Millikan’s Experiment Millikan’s
Atomizer Oil droplets + Oil Microscope Millikan’s Experiment Millikan’s X-rays X-rays give some drops a charge by knocking off electrons Millikan’s Experiment + Millikan’s Experiment Millikan’s + + They put an electric charge on the plates Millikan’s Experiment Millikan’s + + Some drops would hover Millikan’s Experiment Millikan’s + Some drops would hover - - - + + + + ++ + Millikan’s Experiment Millikan’s + + From the mass of the drop and the charge on the plates, he calculated the charge on an electron Rutherford’s Experiment Rutherford’s
Ernest Rutherford English physicist. Ernest (1910) (1910) s Believed the plum pudding model of the Believed atom was correct. atom s Wanted to see how big they are. s Used radioactivity. s Alpha particles - positively charged Alpha pieces given off by uranium. pieces s Shot them at gold foil which can be made Shot a few atoms thick. few
s Rutherford’s experiment Rutherford’s
When the alpha particles hit a When florescent screen, it glows. florescent s Here’s what it looked like (pg 72)
s Lead block Uranium Flourescent Screen Gold Foil He Expected He
The alpha particles to pass through The without changing direction very much. without s Because… s The positive charges were spread out The evenly. Alone they were not enough to stop the alpha particles. stop
s 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 How he explained it Atom is mostly empty. s Small dense, positive piece positive at center. at s Alpha particles Alpha are deflected by are it if they get close it enough. enough.
s + + Modern View Modern
The atom is mostly The empty space. empty s Two regions. s Nucleus- protons protons and neutrons. and s Electron cloudregion where you might find an electron. electron.
s Density and the Atom Density
Since most of the particles went Since through, it was mostly empty. through, s Because the pieces turned so much, Because the positive pieces were heavy. the s Small volume, big mass, big density. s This small dense positive area is the This nucleus. nucleus.
s Other pieces Other
Proton - positively charged pieces 1840 Proton times heavier than the electron. times s Neutron - no charge but the same mass Neutron as a proton. as s Where are the pieces?
s Subatomic particles Subatomic
Relative Actual mass (g) Name Symbol Charge mass Electron Proton Neutron ep+ n0 -1 +1 0 1/1840 9.11 x 10-28 1 1 1.67 x 10-24 1.67 x 10-24 Structure of the Atom Structure
There are two regions. s The nucleus. s With protons and neutrons. s Positive charge. s Almost all the mass. s Electron cloud- most of the volume of Electron an atom. an s The region where the electron can be The found. found.
s Size of an atom Size
s s Atoms are small. Measured in picometers, 10-12 meters. s Hydrogen atom, 32 pm radius. s Nucleus tiny compared to atom. s IF the atom was the size of a stadium, the IF nucleus would be the size of a marble. nucleus
s s Radius of the nucleus is near 10-15m. Density near 1014 g/cm3. Counting the Pieces Counting
Atomic Number = number of protons Atomic number s # of protons determines kind of atom. s the same as the number of electrons in the the neutral atom. the s Mass Number = the number of protons Mass + neutrons. neutrons. s All the things with mass. s NOT on the periodic table
s Isotopes Isotopes
Dalton was wrong. s Atoms of the same element can have Atoms different numbers of neutrons. different s different mass numbers. s called isotopes. called isotopes.
s Symbols Symbols
s Contain the symbol of the element, the Contain mass number and the atomic number. mass Symbols Symbols
s Contain the symbol of the element, the Contain mass number and the atomic number. mass Mass number Atomic number X Naming Isotopes Naming
Put the mass number after the name of Put the element. the s carbon- 12 s carbon -14 s uranium-235
s Symbols Symbols
s Find the Find – number of protons – number of neutrons – number of electrons – Atomic number – Mass Number – Name 24 11 Na Symbols Symbols
s Find Find the – number of protons – number of neutrons – number of electrons – Atomic number – Mass Number
– Name 80 35 Br Symbols Symbols
s if 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
– Name Symbols Symbols
s if if an element has 91 protons and 140 neutrons what is the – Atomic number – Mass number – number of electrons – Complete symbol
– Name Symbols Symbols
s if if an element has 78 electrons and 117 neutrons what is the – Atomic number – Mass number – number of protons – Complete symbol
– Name Atomic Mass Atomic
How heavy is an atom of oxygen? s There are different kinds of oxygen atoms. s More concerned with average atomic mass. More atomic s Based on abundance of each element in Based nature. nature. s Don’t use grams because the numbers Don’t would be too small. would
s Measuring Atomic Mass Measuring
Unit is the Atomic Mass Unit (amu) Unit (amu) s One twelfth the mass of a carbon-12 One atom. s 6 p+ and 6 n0 s Each isotope has its own atomic mass s we get the average using percent we abundance. abundance.
s Calculating averages Calculating
You have five rocks, four with a mass of 50 You g, and one with a mass of 60 g. What is the average mass of the rocks? average s Total mass = 4 x 50 + 1 x 60 = 260 g s Average mass = 4 x 50 + 1 x 60 = 260 g 5 5 s Average mass = 4 x 50 + 1 x 60 = 260 g 5 5 5
s Calculating averages Calculating
Average mass = 4 x 50 + 1 x 60 = 260 g 5 5 5 s Average mass = .8 x 50 + .2 x 60 s 80% of the rocks were 50 grams s 20% of the rocks were 60 grams s Average = % as decimal x mass + Average % as decimal x mass + % as decimal x mass +
s Atomic Mass Atomic
s Calculate the atomic mass of copper if Calculate copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass of 64.93 amu. 64.93 Atomic Mass Atomic
Magnesium has three isotopes. 78.99% Magnesium magnesium 24 with a mass of 23.9850 amu, 10.00% magnesium 25 with a mass of 24.9858 amu, and the rest magnesium 25 with a mass of 25.9826 amu. What is the atomic mass of magnesium? atomic s If not told otherwise, the mass of the If isotope is the mass number in amu
s Atomic Mass Atomic
Is not a whole number because it is an Is average. s are the decimal numbers on the are periodic table. periodic
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