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Atomic Structure Defining the Atom The Element Song by The Best Guy Ever What is an Atom? The smallest part of an element that retains its identity in a chemical reaction. Atomic History http://www.youtube.com/watch?v=VQfOlMs4zFs&featur e=related HISTORY OF THE ATOM 460 BC Democritus develops the idea of atoms he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which could not be divided and called these: ATOMA (greek for indivisible) Historic Models of the Atom Aristotle (384-322 BC) didn’t think there was a limit to the number of times matter could be divided. He knew there were small particles. Air, Fire, Earth, Water HISTORY OF THE ATOM 1808 John Dalton suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS Dalton’s Atomic Theory 1. All elements are composed of atoms (which can’t be divided). 2. Atoms of the same element have the same mass and atoms of different elements have different masses. 3. Compounds contain atoms of more than one element. 4. In a compound, atoms of different elements always combine in the same way. Dalton’s atom Solid sphere Dalton’s Atomic Theory Most of Dalton’s statements are now known to be flawed. As we continue to study the atom, we will talk about discoveries that disproved Dalton’s statements. Scientists have revised the theory due to new discoveries! HISTORY OF THE ATOM 1898 Joseph John Thomson found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON J.J. Thomson, 1897 Discovered the electron, the subatomic particle with a negative charge His experiments involved the use of a cathode ray tube Animation of Thomson’s model JJ Thomson Question and explanation on youtube http://www.youtube.com/watch?v=XU8nMKkzbT8 JJ Thomson Video clip Start at 5:00 and go to about 7:00 HISTORY OF THE ATOM 1904 Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge like plums surrounded by pudding. PLUM PUDDING MODEL Thomson’s Atomic Model Developed the Plum Pudding model. (think of a chocolate chip cookie) Electrons evenly distributed throughout a positively charged material. Plum Pudding Model Sphere of Positive charge e- e- ee- e- HISTORY OF THE ATOM 1910 Ernest Rutherford oversaw Geiger and Marsden carrying out his famous experiment. they fired Helium nuclei at a piece of gold foil which was only a few atoms thick. they found that although most of them passed through. About 1 in 10,000 hit HISTORY OF THE ATOM helium nuclei gold foil helium nuclei They found that while most of the helium nuclei passed through the foil, a small number were deflected and, to their surprise, some helium nuclei bounced straight back. Ernest Rutherford, 1911 Tested theory that electrons were evenly distributed throughout the atom within positively charged material Performed the Gold-Foil Experiment Rutherford animation Another Rutherford Animation Ernest Rutherford If Thomson’s model was correct, most of the alpha particles should pass through with a little deflection Rutherford’s Model Proposed that atoms contain a nucleus, a small, dense, positively-charged sphere in the center of the atom. Atom contains mostly empty space. The nucleus is tiny compared with the atom as a whole. Ernest Rutherford Thomson’s model Rutherford’s model Rutherford’s model: Nuclear Atom e- e- + + + e- Rutherford did NOT know about neutrons! HISTORY OF THE ATOM Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus. He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction However, this was not the end of the story. The Houston Astrodome occupies more than nine acres and seats 60,000 people. If the stadium were a model for an atom, a marble could represent its nucleus! Development of the Atomic Theory Outline Activity HW- please work on page 1 of the Atom Worksheet and your Atomic Theory Outline/Foldable Development of the Atomic Theory Timeline Activity – DAY 2 Show me your timeline!!! Let’s review those great scientists!! Comparing Dalton, JJ Thomson, and Rutherford This is a one question quiz on youtube…. HISTORY OF THE ATOM 1913 Niels Bohr studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons. Bohr’s Atom electrons in orbits nucleus Summary Dalton’s Theory- all matter is made up of atoms, which can’t be divided Thomson’s Model- discovered atoms were made up of smaller particles (these smaller particles are charged) Rutherford’s Theory- discovered the positively charged nucleus Parts of an Atom Atom = nucleus surrounded by one or more electrons Atoms are neutral (no charge) Majority of the atom is empty space. If nucleus were the size of a pencil eraser, the closest electron would be 100 yards away! Subatomic Particles same number of protons as electrons. Protons (+) Neutrons (0) Electrons (-) Nucleus: Tightly packed Protons & Neutrons Electrons Orbiting nucleus @ speed of light!! HELIUM ATOM Shell proton + - N N + electron What do these particles consist of? - neutron ATOMIC STRUCTURE Particle Charge Mass proton + charge 1 neutron No charge 1 electron - charge nil Atomic Number Atomic Number = # of Protons Each Element in the Periodic Table has a different number of Protons, therefore each element has a different, unique, atomic number. When reading the Periodic table notice each element has a unique 1 or 2 letter symbol and “big” & “small” number listed Eureka - Electrons ATOMIC STRUCTURE He 2 4 Atomic number the number of protons in an atom Mass number the number of protons and neutrons in an atom number of electrons = number of protons Can you read these? Atomic Number and Mass Activity Contents of each box Try this for one of the elements with a number between 2 and 12 Atomic number Symbol Element name Mass # Electrical Atomic Charge Remember that Atoms are neutral (no charge) So, the # of protons = # of electrons If you know the Atomic #, you know the # of Protons and also the # of Electrons!! For example: Carbon has an atomic # of 6, it therefore has 6 Protons which has an electrical charge of +6, to make the atom neutral we need 6 negative charges found in the 6 electrons orbiting the nucleus. Mass number Mass number = the total # of Protons & Neutrons ( we don’t worry about the mass of the electrons since they have almost no mass) How many Neutrons are there? Remember: The Atomic # = the # of Protons The mass # = The # of both Protons & Neutrons. Therefore, if you subtract the Atomic # (the number of Protons) from the mass # (the number of both Protons & Neutrons) what is left over must be the number of Neutrons!! For Example w/ Carbon: Mass # -Atomic # = # Neutrons Mass # = 12, Atomic # 6 12 – 6 = 6 Therefore there are 6 neutrons present in the Carbon nucleus If you don’t believe me… just count for yourself. What is an Isotope? Atoms with the same number of protons, but a different number of neutrons. “Same number of protons” means same atomic number, which means same element. “Different number of neutrons” means different mass numbers. Isotopes Can sometimes be represented with dashes and numbers that follow the element. C-14 Pu-246 O-16 O-17 Heavy Water Video clip Information about heavy water Atomic Mass vs. Mass Number What’s the difference??? Atomic mass is also known as atomic weight. Atomic mass is the weighted average mass of an atom of an element based on the relative natural abundance of that element's isotopes. Mass number is a count of the total number of protons and neutrons in an atom's nucleus. Hydrogen has three natural isotopes: 1H, 2H, and 3H. Each isotope has a different mass number. 1H has 1 proton. Its mass number is 1. 2H has 1 proton and 1 neutron. Its mass number is 2. 3H has 1 proton and 2 neutrons. Its mass number is 3. 99.98% of all hydrogen is 1H 0.018% of all hydrogen is 2H 0.002% of all hydrogen is 3H Together, they give a value of atomic mass of hydrogen equal to 1.0079 g/mol. This is like calculating your average in this class! 50% test, 50% everything else!!! So let’s Practice… Chlorine mass number exact weight Silicon percent mass exact abundance number weight percent abundance 35 75.77 28 92.23 37 24.23 29 4.67 30 3.10 The answer for chlorine: 35.453 amu The answer for silicon: 28.086 amu Element Symbol Quiz You need to know the element symbol for the following elements: 1-20 24-30 35,47,50,53 79,80,82,86,88 You will have a quiz on Thursday, Sept 17th I will give you the symbol or the name and you will have to give me the other…there will be NO WORD BANK! Review How many protons and neutrons are there in an atom of 11 B? 5 A 5 protons and 6 neutrons B 5 protons and 11 neutrons C 11 protons and 5 neutrons D 11 protons and 6 neutrons How many neutrons are in an element of Pu-246? A. 94 B. 150 C. 152 D. 246 What are Oxygen-17 and Oxygen-18? How many protons do they have? How many neutrons do they have? Neils Bohr, 1913 From a study of Hydrogen, concluded that an electron travels around the nucleus in circular paths called orbits Each pathway represents an energy level. Only orbits of certain energies are allowed. Electrons can’t exist between orbits. Like rungs on a ladder Niels Bohr Level closest to nucleus has lowest energy Energy must be added for an electron to move up a level. Energy is released when an electron moves down. ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. • first shell a maximum of 2 electrons • second shell a maximum of 8 electrons • third shell a maximum of 18 electrons Bohr’s Planetary Model – looks like planets orbiting the sun!!! How many electrons are present in each orbit? 2 8 18 32 Electron Cloud Model – advanced from Bohr’s model Bohr’s “orbits” are now “principal energy levels”. Bohr was incorrect in assuming that electrons moved like planets in a solar system. The Electron Cloud model shows the MOST LIKELY location of electrons in an atom!! (these are not precise since it’s all based on probability!!) Think of a propeller on an airplane...you can see the blades when they aren’t moving…when it is moving you see only a blur…this is like the electron cloud model!! The number of electrons in each principal energy level is still correct 2, 8, 18, 32 More atoms shown with Bohr’s model Which of the following provides the best analogy for an electron in an atomic orbital? a. a bee buzzing from flower to flower in a garden b. a bird flying high in the sky c. an ant crawling on the surface of a leaf d. a bee buzzing inside a closed jar Quantum Mechanical Model (electron cloud model) Bohr Model Atomic Orbitals Orbital – a region of space around the nucleus where an electron is most likely to be found (think of a map of the school and dots that mark your location every 10 minutes) Electron configuration – the arrangement of electrons in the orbitals of an atom Most stable – electrons are in orbitals with the lowest possible energy Remember!! When electrons move to a higher orbital they GAIN energy!! When electrons move to a lower orbital they RELEASE energy!! Structure of the Atom subatomic particles Proton p+ Positive charge In nucleus mass =1 Neutron no Neutral charge In nucleus mass = 1 Electron eNegative charge In electron cloud mass = 1/1840
