What Are The Two Most Important Properties Of A Telescope – Presentation on theme: “Chapter 3 Atoms: The Building Blocks of Matter. Part 1 From Philosophical Idea to Scientific Theory.” – Presentation text:
3 Foundations of Atomic Theory Particle Theory of Matter Democritus in 400 BC Explained that the fundamental particle of nature is the atom (Greek for “indivisible”). Aristotle believed that all matter is connected (can be divided forever) and did not believe in atoms. Neither had empirical evidence to support their claims.
What Are The Two Most Important Properties Of A Telescope
4 Fast forward to the 18th century Three laws discovered through improved instruments and carefully observed chemical reactions Law of Conservation of Mass – Mass is neither created nor destroyed in a typical chemical reaction or physical change. Law of Definite Proportions – A chemical compound contains the same elements in the same mass proportions, regardless of the size of the sample or the source of the compound. Example: table salt always consists of 39.34% Na and 60.66% chlorine. Law of Multiple Proportions – When two or more compounds are composed of two similar elements, the ratio of the mass of the second element to the given mass of the first element is always a small integer ratio. Example: Carbon and oxygen can combine to form CO 2 or CO.
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5 Exercises (Mass Constancy) If 3.5 g of X reacts with 10.5 g of Y to form compound XY, what is the mass fraction of X in the compound? If 40 g of X reacts with 35 g of Y, what is the mass of the product XY? If 3.5 g of X reacts with 10.5 g of Y to form compound XY, how many grams of Y will react to form XY 2 ? What will be the final mass of XY 2?
6 Exercise (Law of Definite Proportions) 2 unknown compounds are tested. Compound 1 contains 15.0 g of hydrogen and 120.0 g of oxygen. Compound 2 contains 2.0 g of hydrogen and 32.0 g of oxygen. Are the connections the same?
7 Exercises with Multiple Ratios Three compounds containing K and O are compared. Analysis shows that the compounds contain 1.22 g, 2.44 g, and 4.89 g of K per 1.00 g of O, respectively. Show how these data support the law of multiple proportions. First: find K ratios for different compounds. If the ratios are whole numbers, the law supports it.
8 More exercises with multiple ratios… In 100 grams of compound A, there are 57.1 grams of O and 42.9 grams of C. There are 72.7 grams of O and 27.3 grams of C in 100 grams of compound B. show, because these data support the law of several cases. Ratios
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9 1.) If 13 grams of X react with 45 grams of Y to form compound XY, what is the mass percent of X in the compound? 2.) Two unknown connections are tested. Compound 1 contains 32.6 grams of hydrogen and 167.4 grams of carbon. Compound 2 contains 8.0 g of hydrogen and 24.0 g of carbon. Are the connections the same?
10 Dalton’s Atomic Theory John Dalton – Proposed Atomic Theory Considers all three laws: conservation of mass, definite proportions, and multiple proportions. Dalton’s atomic theory includes the following propositions: All matter is composed of atoms. Atoms of a given element are identical in size, mass and all other properties. Atoms cannot be divided, created or destroyed. Atoms of different elements combine together in simple correct proportions and form chemical compounds. In chemical reactions, atoms are separated, combined or rearranged.
11 Modern Atomic Theory Advances in instrumentation have disproved some aspects of Dalton’s theory. Example: It is wrong to assume that atoms cannot be divided into smaller particles and have exactly the same mass. Two important aspects of Dalton’s theory still apply: All matter is composed of atoms. Atoms of one element are different from atoms of another element in terms of properties.
13 Discovery of the Electron Scientific advances made it possible to discover the smaller particles that made up atoms. William Crookes – An electric current passes through a cathode ray tube. We found that current flowing through the tube creates a stream of glowing particles (particles move from the negative end of the tube (cathode) to the positively charged end (anode).
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14 Two results were obtained from the experiments: 1.) Cathode rays are deflected by a magnetic field in the same way as a current-carrying (negatively charged) wire. 2.) Rays are deflected by a negatively charged object.
17 JJ Thomson, 1900 He proved Dalton’s solid atom wrong when he found that these particles had mass but much less than the mass of the hydrogen atom. They concluded that the electron has a very large charge-to-mass ratio. Conducted cathode ray experiments to prove that atoms are divisible. Suggested plum pudding model for Atom.
18 Millikan experiment and oil drop measured the mass of the drop. Applying electric voltage to the top and bottom plates. The voltage required to keep the oil droplets in suspension was measured. He was able to measure the charge of an electron! http://www.youtube.com/watch?v=EV1owO1H2dA www.youtube.com/watch?v=EV1owO1H2dA
19 Ernest Rutherford Discovered the nucleus of the atom by experimenting with gold foil. http://www.youtube.com/watch?v=XBqHkraf8iE http://www.youtube.com/watch?v=XBqHkraf8iE Conclusion that the volume of the nucleus is very small compared to the volume of the whole atom. .
What Are The Two Most Important Properties Of A Telescope?
20 Atomic size Expressed in picometers (pm). 1 pm = 1*10-12 meters = 0.000000000001 meters
22 atomic number is the number of protons in each atom of a given element. It is unique for each element and does not change. Used to identify items.
23 exercises 1. How many protons and electrons are there in each atom? Radon, Rn Titanium, Ti 2. An atom of an element contains 66 electrons. Which case is it? 3. An atom of an element contains 14 protons. Which case is it?
24 Isotopes and mass number The amount of protons and electrons in all neutral atoms of an element is constant, but the number of neutrons can be different Isotopes – atoms of the same element that have different numbers of neutrons Example: hydrogen atoms They have three atoms. Different isotopes Protium – 1 proton/0 neutrons (contains 99.985% of all hydrogen atoms). Deuterium – 1 proton / 1 neutron (0.015%) Tritium – 1 proton / 2 neutrons (radioactive and can be made by humans) Most elements contain a mixture of isotopes. Tin (Sn) has 10 stable isotopes, more than any other element. Mass number – the number of protons and neutrons that make up the nucleus of an isotope. Because electrons are so small, their mass is considered negligible.
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25 Isotope Naming Isotopes are usually identified by their mass numbers. Two methods: Hyphen symbol – consists of a hyphen after the element name followed by the mass number. Example: Tritium is hydrogen 3 because it has 2 neutrons and 1 proton. Example: Uranium-235 Nuclear symbol Mass number written above the line Atomic number written below Following the element symbol
26 With both methods… The number of neutrons is determined by subtracting the atomic number from the mass number. Example: Uranium 235 or 235 92 U (mass number) – (atomic number) = (number of neutrons) 235 (protons + neutrons) – 92 protons = 143 neutrons
29 Relative Atomic Mass The mass of subatomic particles is very small and difficult – Scientists have created a new unit Atomic mass unit (amu) – based on the standard carbon-12 with a mass of 12 amu Neutron – 1.008665 amu = 1.66×10 -24 Gram Proton – 1.007276 amu Electron – 0.0005486 amu
30 Average atomic mass Avg. Atomic mass – weighted average mass of isotopes of that element Average. Atomic mass = (mass x abundance) isotope 1 + (mass x abundance) isotope 2 + … To find the abundance, divide the percentage by 100 (all abundances must be decimals). Atomic mass can help you determine which isotope of that element is most abundant.
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31 Applications of Atomic Mass 1. Boron has two natural isotopes: boron-10 (abundance 19.8%, mass 10.013 amu) and boron-11 (abundance 80.2%, mass 11.009 amu). Calculate the atomic mass of boron 2. Nitrogen has two natural isotopes N-14 and N-15. Its atomic mass is 14.007. Which isotope is more common? explanation
32 Calculate the average atomic mass of lithium, which exists in nature in the form of two isotopes with the following mass and atomic abundance: 6.017 Amu, 7.30% and 7.018 Amu, 92.70%.
33 If out of 100 atoms, 5 atoms have 176, 19 atoms have 177, 27 have a mass of 178, 14 have a mass of 179, and 35 atoms have a mass, what is the atomic mass of hafnium? of 180.0? Iodine consists of 80% 127 I, 17% 126 I and 3% 128 I. Calculate the average atomic mass of iodine.
34 Magnesium has three natural isotopes. 78.70%
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