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Inside an Atom Models of the Atom pp. 510-520 1. What is an atom? Chapter 17 Cannot be divided; for example, a string of beads can be cut in half again and again until you have one 2. What is chemistry? Study of matter 3. What happened in the Scientists began debating the existence of atoms once more; eighteenth century? they were learning about matter and how it changes; they were putting substances together to form new substances and taking substances apart to find out what they were made of; they found that certain substances couldn’t be broken down into simpler substances; they came to realize that all matter is made of elements; for example, iron is an element made of iron atoms so are carbon (carbon atoms), silver (silver atoms), gold (gold atoms), oxygen (oxygen atoms), etc. 4. What is an element? Is matter made of atoms of only one kind 5. Who is John Dalton? An English schoolteacher in the early 19th century who P. 511 pictured the atom as a hard sphere that was the same throughout (like a marble) 6. What did Dalton He combined the idea of elements with the Greek theory of propose? the atom or ideas of the atom 1. Matter is made up of atoms. 2. Atoms cannot be divided into smaller pieces. 3. All the atoms of an element are exactly alike. 4. Different elements are made of different kinds of atoms. 7. Who is William In 1870, an English scientist by the name of William Crookes Crookes? p. 511-512 tested Dalton’s theory by experimenting with a glass tube that had almost all the air removed from it; the glass had two pieces of metal called electrodes (piece of metal that can conduct electricity) sealed inside; when the electrodes were connected to a battery by wires, something flowed from the negative electrode (cathode) to the positive electrode (anode) 8. What are cathode Crookes hypothesized that the green glow in the tube was rays (CRT)? caused by rays or streams of particles; cathode ray tube gots it name because the particles start at the cathode and traveled to the anode; CRT’s used to be in a every TV and computer monitor 9. Who is J.J. In 1897, an English physicist by the name of J.J. Thompson Thompson? tries to disprove Crookes’ theory (Was the greenish glow a light or was it a stream of charged particles?); he placed a magnet beside the tube from Crookes’ experiment and you can see that the beam is bent in the direction of the magnet; light cannot be bent by a magnet so the beam cannot be a light; so Thompson concluded that the beam must be made of charged particles of matter that came from the cathode 10. What else did J.J. Thompson discover? 11. Who is Ernest Rutherford? 12. What are protons? 13. How did Rutherford describe his new model? 14. What are neutrons? 15. After Rutherford’s findings of the nucleus, how did scientists revise the atom model? 16. What particles are in the nucleus of the nuclear atom? 17. Further Developments 18. What is the electron cloud? 1. Electrons (negatively charged particles) (opposite charges attract each other) 2. Revised Dalton’s atom model from the hard sphere that was the same throughout (marble) to a sphere that contains both positive and negative charge atoms dispersed evenly p. 514 In 1906, he tried to disapprove Thompson’s atom model; his experiment had alpha particles aimed at a thin sheet of gold foil 400 nm (nanometers) thick; the foil was surrounded by a fluorescent screen that gave a flash of light each time it was hit by a charged particle; most particles passed right through the foil or veered slightly from a straight line path but some particles bounced right back p. 515; he proved that almost all the mass of the atom and all of its positive charge are crammed into an incredibly small region of space at the center of the atom called the nucleus p. 516 Is a positively charged particle present in the nucleus of all atoms Most alpha particles could move through the foil with little or nor interference because of the empty space that makes up most of the atom; however, if an alpha particle made a direct hit on the nucleus of a gold atom, which has 79 protons, the alpha particle would be strongly repelled and bounce back Would have the same mass as a proton and be electrically neutral, has no charge The nuclear atom has a tiny nucleus tightly packed with positively charged protons and neutral neutrons; negatively charged electrons occupy the space surrounding the nucleus; the number of electrons in a neutral atom equals the number of protons in the atom; for instance, if the ferris wheel in London is 132 m, were the outer edge of the atom, the nucleus would be about the size of a single letter o on a sheet of paper Protons and neutrons Electrons are constant, unpredictable motion and can’t be described easily by an orbit Difficult to know the exact location of an electron at any particular moment More likely to be close to the nucleus rather than further away but they could be anywhere Electrons traveling in a region surrounding the nucleus; electrons are more likely to be close to the nucleus rather than further away because they are attracted to the positive charges of the protons; but they could be anywhere; there are no firm boundaries The Nucleus pp. 521-529 19. What is the atomic number of an element? 20. How are atoms of an element identified? 21. What are isotopes? 22. What is the mass number of an isotope? 23. What occurs in radioactive decay? 24. What occurs in transmutation? 25. Transmutation (difficult) 26. How can you determine when a nucleus will decay? 27. What is carbon dating? The number of protons in the nucleus of an atom of that element; for example, the smallest of the atoms is hydrogen which has 1 proton in its nucleus, so hydrogen’s atomic number is 1; another example, the heaviest naturally occurring element is uranium which has 92 protons so its atomic mass is 92 They are identified by the number or protons because this number never changes without changing the identity of the element Are atoms of the same element that have different numbers of neutrons; for example, the three isotopes of carbon differ in the number of neutrons in each nucleus such as Carbon 12, Carbon 13, and Carbon 14 (p. 521 ) Is the number of neutrons plus protons or you can find the number of neutrons by subtracting the atomic number from the mass number (p. 522) Nuclear particles and energy are released from the nucleus of an atom; for example, Carbon 12 is the most stable isotope of carbon (6 protons and 6 neutrons); some nuclei are unstable because it has too many or too few neutrons such as uranium and plutonium (heavier elements) which causes repulsion build up, the nucleus must release a particle to become stable When the particles that are ejected from a nucleus include protons, the atomic number of the nucleus changes; when this happens, one element into another through radioactive decay Example: smoke detectors make use of radioactive decay; this device contains americium – 241 (a muh RIH shee um), which undergoes transmutation by ejecting energy and an alpha particle (consists of 2 protons and 2 neutrons); together the energy and particles are called radiation; the fast moving alpha particles enable the air to conduct an electric current; as long as the electric current is flowing, the smoke detector is silent; the alarm is triggered when the flow of electric current is interrupted by smoke entering the detector Changed identity p. 523 Loss of beta particles (electrons) p. 524 It is impossible to determine when it will decay; radioactive decay is random; for example, when watching popcorn, you can’t predict which kernel will explode; this is why rate of decay of a nucleus is measured by its half-life (of a radioactive isotope is the amount of time it takes for half of a sample of the element to decay) Scientists have found the study of radioactive decay useful in determining the age of artifacts and fossils; Carbon 14 is used 28. Why can’t carbon dating be used to determine the age of rocks? What can be used to determine the age of rocks? 29. How and why do scientists make synthetic elements? to determine the age of dead animals, plants, and organisms, the amount of carbon 14 remains in constant balance with the levels of the isotope in the atmosphere or ocean; this balance occurs because living organisms take in and release carbon carbon dating can only be used on things that have been alive; however, geologists examine the decay of uranium; uranium 238 decays to lead 206 with a half life of 4.5 billion years; by determining the amount of uranium to lead, they can determine the age of a rock A. By smashing atomic particles into a target element; the absorbed particle converts the target element into another element with a higher atomic number; this new element is called synthetic element because it is made by humans; these artificial transmutations have created elements that do not exist in nature such as elements with atomic numbers 93 to 112, 114, 116, and 118. B. Radioactive isotopes are used in hospitals and clinics using specially designed equipment C. Tracer elements are used to diagnose disease and to study environmental conditions D. Radioactive isotopes is introduced into living system which if followed by a device that detects radiation while it decays; these devices often present the results of a photograph or a display on a screen; the isotopes chosen for medical purposes have short half-lives, which allows them to be used without the risk of exposing living organisms to prolonged radiation E. Medical uses of isotope to diagnose problems with the thyroid, digestion problems, circulation and detect cancer F. Environmental uses to detect how a plant uses phosphorus to grow and reproduce, how pesticides moves through the ecosystem