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Chemistry

Explore the atomic theory and the structure of atoms in this chapter. Learn about the laws of definite proportions, conservation of mass, and multiple proportions. Discover Dalton's atomic theory and the modifications made to it. Study the experiments conducted by scientists like J.J. Thomson and Ernest Rutherford that led to our current understanding of atoms.

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Chemistry

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  1. Chemistry Chapter 3 Atoms and Moles

  2. Chapter 3 Atoms and Moles The atomic Theory: states that atoms are the building blocks of all matter What do you think an atom looks like? Section 1 – Substances are made of atoms Incorrect More Accurate

  3. Chapter 3 Atoms and Moles The Law of Definite Proportions states that two samples of a given compound are made of the same elements in exactly the same proportions by mass regardless of the sizes or sources of the samples. Table salt (sodium chloride) is an example that shows the law of definite proportions. Any sample of table salt consists of two elements in the following proportions by mass: 60.66% chlorine and 39.34% sodium Section 1 – Substances are made of atoms

  4. Chapter 3 Atoms and Moles The Law of Conservation of Mass states that the mass of the reactants in a reaction equals the mass of the products Section 1 – Substances are made of atoms

  5. Chapter 3 Atoms and Moles The Law of Multiple Proportions the law that states that when two elements combine to form two or more compounds, the mass of one element that combines with a given mass of the other is in the ratio of small whole numbers Section 1 – Substances are made of atoms

  6. Chapter 3 Atoms and Moles Dalton’s Atomic Theory According to Dalton, elements are composed of only one kind of atom and compounds are made from two or more kinds of atoms. Section 1 – Substances are made of atoms

  7. Chapter 3 Atoms and Moles Dalton’s atomic theory can be summarized by the following statements: 1. All matter is composed of extremely small particles called atoms, which cannot be subdivided, created, or destroyed. 2. Atoms of a given element are identical in their physical and chemical properties. Section 1 – Substances are made of atoms 3. Atoms of different elements differ in their physical and chemical properties. 4. Atoms of different elements combine in simple, whole-number ratios to form compounds. 5. In chemical reactions, atoms are combined, separated, or rearranged but never created, destroyed, or changed.

  8. Chapter 3 Atoms and Moles Because some parts of Dalton’s theory have been shown to be incorrect, his theory has been modified and expanded as scientists learn more about atoms. Section 1 – Substances are made of atoms

  9. Chapter 3 Atoms and Moles For Homework: 1. Do Concept Review: Section 1 – Substances are made of atoms 2. Read Chapter 3, Section 2 - Structure of Atoms

  10. Chapter 3 Atoms and Moles Experiments by several scientists in the mid-1800s led to the first change to Dalton’s atomic theory. Section 2 – Structure of Atoms

  11. Chapter 3 Atoms and Moles The Discovery of Electrons by J.J. Thompson Mid 1800’s To study current, Thomson pumped most of the air out of a glass tube. He then applied a voltage to two metal plates, called electrodes, which were placed at either end of the tube. One electrode, called the anode, was attached to the positive terminal of the voltage source, so it had a positive charge. The other electrode, called a cathode, had a negative charge because it was attached to the negative terminal of the voltage source. Thomson observed a glowing beam that came out of the cathode and struck the anode and the nearby glass walls of the tube. So, he called these rays cathode rays. Thomson knew the rays must have come from the atoms of the cathode because most of the atoms in the air had been pumped out of the tube. Thomson also observed that when a small paddle wheel was placed in the path of the rays, the wheel would turn. This observation suggested that the cathode rays consisted of tiny particles that were hitting the paddles of the wheel. Section 2 – Structure of Atoms

  12. Chapter 3 Atoms and Moles Section 2 – Structure of Atoms Thomson’s experiments showed that a cathode ray consists of particles that have mass and a negative charge.

  13. Chapter 3 Atoms and Moles Thomson’s experiments showed that a cathode ray consists of particles that have mass and a negative charge. These particles are called electrons Section 2 – Structure of Atoms

  14. Chapter 3 Atoms and Moles Thomson proposed that the electrons of an atom were embedded in a Positively charged ball of matter. His picture of an atom, which is shown in was named the plum-pudding model Section 2 – Structure of Atoms

  15. Chapter 3 Atoms and Moles The Discovery of Nucleus by Ernest Rutherford 1909 Rutherford’s team of researchers carried out the experiment where a beam of small, positively charged particles, called alpha particles, was directed at a thin gold foil. The team measured the angles at which the particles were deflected from their former straight-line paths as they came out of the foil. Rutherford found that most of the alpha particles shot at the foil passed straight through the foil. But a very small number of particles were deflected, in some cases backward. He went on to reason that only a very concentrated positive charge in a tiny space within the gold atom could possibly repel the fast-moving, positively charged alpha particles enough to reverse the alpha particles’ direction of travel. Rutherford also hypothesized that the mass of this positive-charge containing region, called the nucleus, must be larger than the mass of the alpha particle. Section 2 – Structure of Atoms

  16. Chapter 3 Atoms and Moles Section 2 – Structure of Atoms

  17. Chapter 3 Atoms and Moles Section 2 – Structure of Atoms This part of the model of the atom is still considered true today. The nucleus is the dense, central portion of the atom. The nucleus has all of the positive charge, nearly all of the mass, but only a very small fraction of The volume of the atom.

  18. Chapter 3 Atoms and Moles By measuring the numbers of alpha particles that were deflected and the angles of deflection, scientists calculated the radius of the nucleus to be less than 1/10,000 of the radius of the whole atom. Section 2 – Structure of Atoms If the nucleus of an atom were the size of a marble, then the whole atom would be about the size of a football stadium.

  19. Chapter 3 Atoms and Moles The positively charged particles that repelled the alpha particles in the gold foil experiments and that compose the nucleus of an atom are called protons. The charge of a proton was calculated to be exactly equal in magnitude but opposite in sign to the charge of an electron. Later experiments showed that the proton’s mass is almost 2000 times the mass of an electron. Section 2 – Structure of Atoms

  20. Chapter 3 Atoms and Moles About 30 years after the discovery of the electron, Irene Joliot-Curie Discovered that when alpha particles hit a sample of beryllium, a beam that could go through almost anything was produced. The British scientist James Chadwick found that this beam was not deflected by electric or magnetic fields. He concluded that the particles Carried no electric charge. Further investigation showed that these neutral particles, which were named neutrons are part of all atomic nuclei Section 2 – Structure of Atoms

  21. Chapter 3 Atoms and Moles All atoms consist of protons and electrons. Most atoms also have neutrons. Protons and neutrons make up the small, dense nuclei of atoms. The electrons occupy the space surrounding the nucleus. For example, an oxygen atom has protons and neutrons surrounded by electrons. But that description fits all other atoms, such as atoms of carbon, nitrogen, silver, and gold. Elements differ from each other in the number of protons their atoms contain. Section 2 – Structure of Atoms

  22. Chapter 3 Atoms and Moles Atomic Number and Mass Number The number of protons that an atom has is known as the atom’s atomic number The mass number is equal to the total number of particles of the nucleus, that is protons plus neutrons Section 2 – Structure of Atoms Unlike the atomic number, which is the same for all atoms of an element, mass number can vary among atoms of a single element. In other words, all atoms of an element have the same number of protons, but they can have different numbers of neutrons. These atoms of the same element are called isotopes.

  23. Chapter 3 Atoms and Moles Calculating Proton, Electron and Neutron quantity Proton Quantity is always equal to your atomic number. How many protons are in a silver atom? 47 protons Section 2 – Structure of Atoms Which element has 25 protons in the nucleus? Manganese

  24. Chapter 3 Atoms and Moles Calculating Proton, Electron and Neutron quantity Neutron Quantity is always equal to your mass – atomic number How many neutrons in an aluminum atom that has a mass of 27amu? 14 neutrons Section 2 – Structure of Atoms What is the mass of an atom of Iron that contains 30 neutrons? 56 amu

  25. Chapter 3 Atoms and Moles Calculating Proton, Electron and Neutron quantity Electron Quantity using the following rules: For neutral atom: Electron quantity is equal to proton quantity Section 2 – Structure of Atoms For positively charged atoms: Electron quantity is equal to proton quantity minus the charge For negatively charged atoms: Electron quantity is equal to proton quantity plus the charge

  26. Chapter 3 Atoms and Moles Calculating Proton, Electron and Neutron quantity How many electrons are in an oxygen atom with a -2 charge? 10 How many electron in an atom of Potassium with a +1 charge? 18 Section 2 – Structure of Atoms What is the charge of a fluorine atom with 10 electrons? Negative 1 What is the charge of a titanium atom with 22 electrons? Neutral

  27. Chapter 3 Atoms and Moles 1 amu 1+ 1- 0 amu Section 2 – Structure of Atoms Neutral 1 amu

  28. How to display atoms with mass and charge Mass number Atomic Charge 22 + Na 10 Atomic Number Carbon – 14 or 14C or C-14is a carbon atom with a mass of 14amu N-3 is a nitrogen atom with a charge of negative 3

  29. 25 +7 55 25 -1 I 53 74 30 Zn 28 37

  30. Neutral Xe 131 54 50 38 38 +2 76 Os 72 190 10 8 O 10 29 36 29 27 Rh 42 45 103 64 48 48 +2 42 33 +3 33 +2 12 Mg 12 Ca 18 21 20 92 86 U 238 Fr 87 223 87

  31. All atoms of an element have the same atomic number and the same number of protons. However, atoms do not necessarily have the same number of neutrons. Atoms of the same element that have different numbers of neutrons are called isotopes

  32. How to calculate the average atomic mass on an element. Use the formula below: (mass of atom1 x % quantity1) + (mass of atom2 x % quantity2) +…….. Average Atomic Mass = 100 Average Atomic Mass = (204 x 1.4) + (206 x 24.1) + (207 x 22.1) + (208 x 52.4) 100 Answer = 207.2 amu

  33. Sample Questions In a sample of the element potassium, each atom has 1. 19 protons 2. 20 neutrons 3. 39 protons and neutrons 4. 39 neutrons In a sample of neutral copper, all atoms have atomic numbers which are 1. the same and the atoms have the same number of electrons 2. the same, but the atoms have a different number of electrons 3. different, but the atoms have the same number of electrons 4. different and the atoms have a different number of electrons What is the mass number of an atom which contains 28 protons, 28 electrons and 34 neutrons? 1. 28 2. 56 3. 62 4. 90

  34. Sample Questions Which of the following atoms has the greatest nuclear charge? 1. Al 2. Ar 3. Si 4. Na An atom of carbon-14 contains 1. 8 protons, 6 neutrons and 6 electrons 2. 6 protons, 6 neutrons and 8 electrons 3. 6 protons, 8 neutrons and 8 electrons 4. 6 protons, 8 neutrons and 6 electrons Which particle contains the greatest number of electrons? 1. Na 2. Na+ 3. F 4. F-

  35. Sample Questions An electron has a charge of 1. -1 and the same mass as a proton 2. +1 and the same mass as a proton 3. -1 and a smaller mass than a proton 4. +1 and a smaller mass than a proton What is the total number of electrons in a Cr3+ ion? 1. 18 2. 21 3. 24 4. 27 A particle of matter contains six protons, seven neutrons, and six electrons. This particle must be a 1. neutral carbon atom 2. neutral nitrogen atom 3. positively charged carbon ion 4. positively charged nitrogen ion

  36. Sample Questions If 75.0% of the isotopes of an element have a mass of 35.0 amu and 25.0% of the isotopes have a mass of 37.0 amu, what is the atomic mass of the element? 1. 35.0 amu 2. 35.5 amu 3. 36.0 amu 4. 37.0 amu Which symbol represents an isotope of carbon?

  37. Sample Questions All isotopes of a given element must have the same 1. atomic mass 2. atomic number 3. mass number 4. number of neutrons As the number of neutrons in the nucleus of a given atom of an element increases, the atomic number of that element 1. decreases 2. increases 3. remains the same Which symbols represent atoms that are isotopes of each other?

  38. Chapter 3 Atoms and Moles Section 3 Electron Configuration Rutherford’s Model Proposed Electron Orbits The experiments of Rutherford’s team led to the replacement of the Plumpudding model of the atom with a nuclear model of the atom. Rutherford suggested that electrons, like planets orbiting the sun, revolve around the nucleus in circular or elliptical orbits.

  39. Chapter 3 Atoms and Moles Section 3 Electron Configuration Bohr’s Model Confines Electrons to Energy Levels The Rutherford model of the atom, in turn, was replaced only two years later by a model developed by Niels Bohr, a Danish physicist. The Bohr model describes electrons in terms of their energy levels. According to Bohr’s model, electrons can be only certain distances from the nucleus. Each distance corresponds to a certain quantity of energy that an electron can have.

  40. Chapter 3 Atoms and Moles Section 3 Electron Configuration Electrons Act Like Both Particles and Waves In 1924, Louis de Broglie pointed out that the behavior of electrons according to Bohr’s model was similar to the behavior of waves. The present-day model of the atom, which takes into account both the particle and wave properties of electrons. According to this model, electrons are located in regions called Orbitals around a nucleus that correspond to specific energy levels. Orbitals are regions where electrons are likely to be found. Orbitals are sometimes called electron clouds because they do not have sharp boundaries. When an orbital is drawn, it shows where electrons are most likely to be. Because electrons can be in other places, the orbital has a fuzzy boundary like a cloud.

  41. Chapter 3 Atoms and Moles Section 3 Electron Configuration Electron Configurations The arrangement of electrons in an atom is usually shown by writing an electron configuration. Like all systems in nature, electrons in atoms tend to assume arrangements that have the lowest possible energies. An electron configuration of an atom shows the lowest-energy arrangement of the electrons for the element.

  42. Chapter 3 Atoms and Moles Section 3 Electron Configuration Principle Energy Levels (electron shells) Name Max # of e- 1 2 2 8 3 18 4 32 5 32 6 32 7 32

  43. Chapter 3 Atoms and Moles Section 3 Electron Configuration Two types of electron configuration: Ground state: When electrons are all found in the lowest possible principle energy levels (electron shell). Excited state: When one or more electrons have “jumped” to a higher principle energy level (electron shell). Valence electrons: The electrons found in the outermost principle energy level (electron shell) Octet Rule: Atoms will gain or lose electrons to try to have only 8 electrons in the last principle energy level (electron shell). Very small atoms only need 2 electrons to satisfy this rule.

  44. Chapter 3 Atoms and Moles Section 3 Electron Configuration Sample Questions Which electron configuration is correct for a sodium with a 1+ charge? 1. 2-7 2. 2-8 3. 2-8-1 4. 2-8-2 How many electrons are in an Fe2+ ion? 1. 24 2. 26 3. 28 4. 56

  45. Chapter 3 Atoms and Moles Section 3 Electron Configuration Sample Questions Which ion has the same electron configuration as an H- ion? 1. Cl- 2. F- 3. K+ 4. Li+ What is the total number of electrons in the valence shell of an atom of aluminum in the ground state? 1. 8 2. 13 3. 3 4. 10

  46. Chapter 3 Atoms and Moles Section 3 Electron Configuration Sample Questions Which element has an atom with the electron configuration 2-8-8-2? 1. Mg 2. Ni 3. Ca 4. Ge Which set of symbols represents atoms with valence electrons in the same electron shell? 1. Ba, Br, Bi 2. Sr, Sn, I 3. O, S, Te 4. Mn, Hg, Cu

  47. Chapter 3 Atoms and Moles Section 3 Electron Configuration Sample Questions Which symbol represents a particle that has the same total number of electrons as S2-? 1. O2- 2. Si 3. Se2- 4. Ar Which of these elements has an atom that completes the octet rule? 1. Ne 2. Cl 3. Ca 4. Na

  48. Chapter 3 Atoms and Moles Section 3 Electron Configuration Ions: atoms that have lost or gained an electron Cation: an atom that has lost at least one electron, thereby becoming positively charged. Anion: an atom that has gained at least one electron, thereby becoming negatively charged.

  49. Chapter 3 Atoms and Moles Section 3 Electron Configuration Sample Questions What is the total number of valence electrons in a fluorine atom in the ground state?  1. 5  2. 2  3. 7  4. 9

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