1. Atoms: The Building Blocks of Matter Chapter 3

2. SC Standard C.5.9 – Analyze a chemical process to account for the weight of all reagents and solvents by following the appropriate material balance procedures. C.5.9 – Analyze a chemical process to account for the weight of all reagents and solvents by following the appropriate material balance procedures.

3. Objectives Explain the law of conservation of mass, the law of definite proportions, and the law of multiple proportions. Explain the law of conservation of mass, the law of definite proportions, and the law of multiple proportions. Summarize the five essential points of Dalton’s atomic theory. Summarize the five essential points of Dalton’s atomic theory. Explain the relationship between Dalton’s atomic theory and the law of conservation of mass, the law of definite proportions, and the law of multiple proportions. Explain the relationship between Dalton’s atomic theory and the law of conservation of mass, the law of definite proportions, and the law of multiple proportions.

4. History Democritus of Abdera: In the 4th century B.C., he suggested the existence of atoms. In the 4th century B.C., he suggested the existence of atoms. He called nature’s basic particle an atom, meaning indivisible. He called nature’s basic particle an atom, meaning indivisible. No experimental support No experimental support remained speculation until the eighteenth century remained speculation until the eighteenth century

5. History Aristotle (after Democritus) Did not believe in the existence atoms. Did not believe in the existence atoms. Thought all matter was continuous. Thought all matter was continuous. His opinion was accepted for nearly 2000 years! His opinion was accepted for nearly 2000 years! Like Democritus, his idea had no experimental support Like Democritus, his idea had no experimental support

6. John Dalton 2000 years later (after Democritus and Aristotle) 2000 years later (after Democritus and Aristotle) Studied the ratio in which elements combined in chemical reactions Studied the ratio in which elements combined in chemical reactions Came up with a hypothesis which later became a theory based on his observations Came up with a hypothesis which later became a theory based on his observations

7. John Dalton’s Atomic Theory All matter is composed of extremely small particles called atoms. All matter is composed of extremely small particles called atoms. Atoms of a given element are identical*. Atoms of a given element are identical*. Atoms cannot be subdivided*, created, or destroyed. Atoms cannot be subdivided*, created, or destroyed. Atoms of different elements combine in simple whole number ratios to form chemical compounds. Atoms of different elements combine in simple whole number ratios to form chemical compounds. In chemical reactions, atoms are combined, separated, or rearranged. In chemical reactions, atoms are combined, separated, or rearranged.

8. John Dalton’s Atomic Theory ** Most of the theory is accepted today** ** Most of the theory is accepted today** One important change is atoms are now known to be divisible One important change is atoms are now known to be divisible atoms can be broken down into subatomic particles atoms can be broken down into subatomic particles protons protons neutrons neutrons electrons electrons atom “smashers” break them apart atom “smashers” break them apart

9. John Dalton’s Atomic Theory Another important change is that we now know that a given element can have atoms with different masses (ie – they are not identical) Another important change is that we now know that a given element can have atoms with different masses (ie – they are not identical)

10. Modern Atomic Theory Important Concepts All matter is composed of atoms. Atoms of any one element differ in properties from atoms of another element.

11. Foundations of Atomic Theory In the 1700s, there was controversy as to whether elements always combine in the same ratio when forming a particular compound. In the 1700s, there was controversy as to whether elements always combine in the same ratio when forming a particular compound. In the 1790s, scientists began looking at quantitative analysis of chemical reactions. In the 1790s, scientists began looking at quantitative analysis of chemical reactions.

12. Foundations of Atomic Theory The transformation of a substance or substances into one or more new substances is known as a chemical reaction. The transformation of a substance or substances into one or more new substances is known as a chemical reaction. Law of conservation of mass: mass is neither created nor destroyed during ordinary chemical reactions or physical changes Law of conservation of mass: mass is neither created nor destroyed during ordinary chemical reactions or physical changes

13. Foundations of Atomic Theory Law of Conservation of Mass

14. Foundations of Atomic Theory Law of Conservation of Mass

15. Foundations of Atomic Theory Law of definite proportions: a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound (see pg.68) Law of definite proportions: a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound (see pg.68) Law of multiple proportions: if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers Law of multiple proportions: if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers

16. Foundations of Atomic Theory Law of Multiple Proportions

17. SC Standard C.2.2 – Summarize atomic properties (including electron configuration, ionization energy, electron affinity, atomic size, and ionic size) C.2.2 – Summarize atomic properties (including electron configuration, ionization energy, electron affinity, atomic size, and ionic size)

18. Objectives Summarize the observed properties of cathode rays that led to the discovery of the electron. Summarize the observed properties of cathode rays that led to the discovery of the electron. Summarize the experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus. Summarize the experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus. List the properties of protons, neutrons, and electrons. List the properties of protons, neutrons, and electrons. Define atom. Define atom.

19. The Structure of the Atom Atoms are composed of several basic types of smaller particles. Atoms are composed of several basic types of smaller particles. The number and arrangement of these particles with an atom determines that atom’s chemical properties. The number and arrangement of these particles with an atom determines that atom’s chemical properties. An atom is the smallest particle of an element that retains the chemical properties of that element. An atom is the smallest particle of an element that retains the chemical properties of that element.

20. The Structure of the Atom All atoms consist of two regions. All atoms consist of two regions. The nucleus is a very small region located at the center of an atom. The nucleus is a very small region located at the center of an atom. It contains protons (+ charge) and neutrons (no charge). It contains protons (+ charge) and neutrons (no charge). Surrounding the nucleus is a region occupied by electrons (- charge). Surrounding the nucleus is a region occupied by electrons (- charge). Subatomic Particles = protons, neutrons, and electrons Subatomic Particles = protons, neutrons, and electrons

21. Discovery of the Electron J.J. Thomson’s cathode ray experiment J.J. Thomson’s cathode ray experiment Discovered in 1897 Discovered in 1897 "cathode rays" pass from negative electrode towards positive electrode in an evacuated tube "cathode rays" pass from negative electrode towards positive electrode in an evacuated tube made observations through simple tests of the “cathode rays” and developed hypotheses made observations through simple tests of the “cathode rays” and developed hypotheses

22. J.J. Thomson’s Cathode Ray Experiment

23. Discovery of the Electron example hypothesis: cathode rays are streams of electrons example hypothesis: cathode rays are streams of electrons calculated mass to charge ratio for electrons by observing bending of cathode rays in electric and magnetic fields calculated mass to charge ratio for electrons by observing bending of cathode rays in electric and magnetic fields

24. observationshypothesis ray properties are independent of the cathode material... cathode ray stuff is a component of all materials (ie – electrons must be in all materials) cathode rays bend near magnets... magnets bend the paths of moving charged particles; maybe cathode rays are streams of moving charged particles rays bend towards a positively charged plate rays impart a negative charge to objects they strike... cathode rays are streams of negative charges

25. Discovery of the Electron Other observations during cathode ray experiments Other observations during cathode ray experiments cathode rays don’t bend around small obstacles or cast sharp shadows cathode rays don’t bend around small obstacles or cast sharp shadows can turn paddlewheels placed in their path can turn paddlewheels placed in their path travel in straight lines travel in straight lines

26. Electrons Electrons have energy and the further from the nucleus an electron is the more energy it has Electrons have energy and the further from the nucleus an electron is the more energy it has Electrons are found in electron cloud which has energy levels Electrons are found in electron cloud which has energy levels There are a maximum amount of electrons that can occupy each energy level. There are a maximum amount of electrons that can occupy each energy level. When an outer level is full the atom is the most stable. When an outer level is full the atom is the most stable.

27. Electrons

28. Discovery of the Atomic Nucleus In the early part of the last century, the accepted model of the atom was proposed by J J Thomson. In the early part of the last century, the accepted model of the atom was proposed by J J Thomson. It was called the “plum pudding” model. It was called the “plum pudding” model. This consisted of a matrix of protons in which were embedded electrons. This consisted of a matrix of protons in which were embedded electrons. Ernest Rutherford (1871 – 1937) used alpha particles to study the nature of atomic structure. Ernest Rutherford (1871 – 1937) used alpha particles to study the nature of atomic structure.

29. Discovery of the Atomic Nucleus Rutherford Scattering

30. Gold Foil Experiment

32. Rutherford was using alpha particles (helium nuclei) as nuclear bullets to smash up the atoms; he wanted to see atoms bursting like watermelons. But… Rutherford was using alpha particles (helium nuclei) as nuclear bullets to smash up the atoms; he wanted to see atoms bursting like watermelons. But… …instead of bits of atom, Rutherford found that only a small proportion of the alpha particles were deflected, while an even smaller proportion bounced right back. …instead of bits of atom, Rutherford found that only a small proportion of the alpha particles were deflected, while an even smaller proportion bounced right back.

33. …his observations are best illustrated with this diagram

34. Gold Foil Experiment: Conclusions From analysis of these observations he concluded: From analysis of these observations he concluded: Most of the atom was empty space. The positive charge was concentrated in a very small space. Most of the atom was empty space. The positive charge was concentrated in a very small space. The radius of the nucleus was in the order of 3  10 -14 m. The radius of the nucleus was in the order of 3  10 -14 m. The alpha particles that were deflected back had to be traveling in a line with the nucleus. The alpha particles that were deflected back had to be traveling in a line with the nucleus.

35. Gold Foil Experiment: Follow-up Rutherford’s estimates were not far off. Later research has shown the nuclear radius to be in the order of 1.5  10 -14 m. However the boundary is not sharp, but rather fuzzy, as the nucleus is a very dynamic entity. Rutherford’s estimates were not far off. Later research has shown the nuclear radius to be in the order of 1.5  10 -14 m. However the boundary is not sharp, but rather fuzzy, as the nucleus is a very dynamic entity.

36. Composition of the Atomic Nucleus Located in the center of the atom Located in the center of the atom It is very tiny compared to the entire atom. It is very tiny compared to the entire atom. The nucleus has a positive charge The nucleus has a positive charge protons positive and neutrons have no charge protons positive and neutrons have no charge Overall, atoms are neutral (# of protons = # of electrons.) Overall, atoms are neutral (# of protons = # of electrons.) FYI: Like charges repel one another and opposite charges are attracted to one another (Watch This) http://www.youtube.com/watch?v=kypne21A0R4 http://www.youtube.com/watch?v=kypne21A0R4

37. Composition of the Atomic Nucleus Nuclei (plural for nucleus) are composed of "nucleons": protons and neutrons Nuclei (plural for nucleus) are composed of "nucleons": protons and neutrons Mass is measured in atomic mass units (amu) Mass is measured in atomic mass units (amu)

38. Composition of the Atomic Nucleus Forces in the Nucleus When two protons are extremely close to each other, there is a strong attraction between them. When two protons are extremely close to each other, there is a strong attraction between them. A similar attraction exists when neutrons are very close to each other or when protons and neutrons are very close together. A similar attraction exists when neutrons are very close to each other or when protons and neutrons are very close together. The short-range proton-neutron, proton-proton, and neutron-neutron forces that hold the nuclear particles together are referred to as nuclear forces. The short-range proton-neutron, proton-proton, and neutron-neutron forces that hold the nuclear particles together are referred to as nuclear forces.

39. Forces

41. Subatomic Particles Neutrons Neutrons neutral charge neutral charge found in nucleus found in nucleus Protons Protons positive charge positive charge found in nucleus found in nucleus Electrons Electrons negative charge negative charge found outside nucleus in electron cloud found outside nucleus in electron cloud

42. Comparing Subatomic Particles ParticleCharge Mass (kg) Location Proton+1 1.67 x 10 -27 Nucleus Neutron0 Nucleus Electron 9.11 x 10 -31 Outside Nucleus http://www.youtube.com/watch?v=auhHl5-6VdY

43. SC Standards C.4.4 – Apply the concept of moles to determine the number of particles of a substance in a chemical reaction, the percent composition of a representative compound, the mass proportions, and the mole-mass relationships. C.4.4 – Apply the concept of moles to determine the number of particles of a substance in a chemical reaction, the percent composition of a representative compound, the mass proportions, and the mole-mass relationships.

44. Objectives Explain what isotopes are. Explain what isotopes are. Define atomic number and mass number, and describe how they apply to isotopes. Define atomic number and mass number, and describe how they apply to isotopes. Given the identity of a nuclide, determine its number of protons, neutrons, and electrons. Given the identity of a nuclide, determine its number of protons, neutrons, and electrons. Define mole, Avogadro’s number, and molar mass, and state how all three are related. Define mole, Avogadro’s number, and molar mass, and state how all three are related. Solve problems involving mass in grams, amount in moles, and number of atoms of an element. Solve problems involving mass in grams, amount in moles, and number of atoms of an element.

45. Atomic Number Atoms of different elements have different numbers of protons. Atoms of different elements have different numbers of protons. Atoms of the same element all have the same number of protons. Atoms of the same element all have the same number of protons. The atomic number (Z) of an element is the number of protons in each atom of that element. The atomic number (Z) of an element is the number of protons in each atom of that element.

46. Atomic Number

47. Isotopes Isotopes are atoms of the same element that have different masses. Isotopes are atoms of the same element that have different masses. The isotopes of a particular element all have the same number of protons and electrons but different numbers of neutrons. The isotopes of a particular element all have the same number of protons and electrons but different numbers of neutrons. Most of the elements consist of mixtures of isotopes. Most of the elements consist of mixtures of isotopes. Isotopes of the same element do not differ significantly in their chemical behavior. Isotopes of the same element do not differ significantly in their chemical behavior.

48. Mass Number The mass number is the total number of protons and neutrons that make up the nucleus of an atom. The mass number is the total number of protons and neutrons that make up the nucleus of an atom. Isotopes of the same element will have identical atomic numbers, but different mass numbers due to differing numbers of neutrons. Isotopes of the same element will have identical atomic numbers, but different mass numbers due to differing numbers of neutrons.

49. Designating Isotopes Hyphen notation: The mass number is written with a hyphen after the name of the element. Hyphen notation: The mass number is written with a hyphen after the name of the element. example - uranium-235 example - uranium-235 Nuclear symbol: The superscript indicates the mass number and the subscript indicates the atomic number. Nuclear symbol: The superscript indicates the mass number and the subscript indicates the atomic number. example – (see page 79) example – (see page 79)

50. Designating Isotopes The number of neutrons is found by subtracting the atomic number from the mass number. The number of neutrons is found by subtracting the atomic number from the mass number. mass # - atomic # = # of neutrons mass # - atomic # = # of neutrons Nuclide is a general term for a specific isotope of an element. Nuclide is a general term for a specific isotope of an element.

51. Designating Isotopes Sample Problem A (pg 79) Sample Problem A (pg 79) How many protons, electrons, and neutrons are there in an atom of chlorine-37?

52. Relative Atomic Masses The standard used by scientists to compare units of atomic mass is the carbon-12 atom, which has been arbitrarily assigned a mass of exactly 12 atomic mass units, or 12 amu. The standard used by scientists to compare units of atomic mass is the carbon-12 atom, which has been arbitrarily assigned a mass of exactly 12 atomic mass units, or 12 amu. One atomic mass unit, or 1 amu, is exactly 1/12 the mass of a carbon-12 atom. One atomic mass unit, or 1 amu, is exactly 1/12 the mass of a carbon-12 atom. The atomic mass of any atom is determined by comparing it with the mass of the carbon- 12 atom. The atomic mass of any atom is determined by comparing it with the mass of the carbon- 12 atom.

53. Average Atomic Masses of Elements Average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element. Average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element. Calculating Average Atomic Mass Calculating Average Atomic Mass The average atomic mass of an element depends on both the mass and the relative abundance of each of the element’s isotopes. The average atomic mass of an element depends on both the mass and the relative abundance of each of the element’s isotopes.

54. Average Atomic Masses of Elements The average atomic mass of copper can be calculated by multiplying the atomic mass of each isotope by its relative abundance (expressed in decimal form) and adding the results. The average atomic mass of copper can be calculated by multiplying the atomic mass of each isotope by its relative abundance (expressed in decimal form) and adding the results. Example - Copper consists of 69.15% Cu-63, which has an atomic mass of 62.929 601 amu, and 30.85% Cu-65, which has an atomic mass of 64.927 794 amu. Example - Copper consists of 69.15% Cu-63, which has an atomic mass of 62.929 601 amu, and 30.85% Cu-65, which has an atomic mass of 64.927 794 amu.

55. Average Atomic Masses of Elements (0.6915 × 62.929 601 amu) + (0.3085 × 64.927 794 amu) = 63.55 amu (0.6915 × 62.929 601 amu) + (0.3085 × 64.927 794 amu) = 63.55 amu The calculated average atomic mass of naturally occurring copper is 63.55 amu. The calculated average atomic mass of naturally occurring copper is 63.55 amu.

56. Relating Mass to Numbers of Atoms The mole is the SI unit for amount of substance. The mole is the SI unit for amount of substance. A mole (abbreviated mol) is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12. A mole (abbreviated mol) is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12. Moles of different elements will be different masses. Moles of different elements will be different masses.

57. Avogadro’s Number Avogadro’s Number Avogadro’s Number 6.022 1415 × 10 23 6.022 1415 × 10 23 It is the number of particles in exactly one mole of a pure substance. It is the number of particles in exactly one mole of a pure substance.

58. Molar Mass The mass of one mole of a pure substance is called the molar mass of that substance. The mass of one mole of a pure substance is called the molar mass of that substance. Molar mass is usually written in units of g/mol. Molar mass is usually written in units of g/mol. The molar mass of an element is numerically equal to the atomic mass of the element in atomic mass units. The molar mass of an element is numerically equal to the atomic mass of the element in atomic mass units.

59. Gram/Mole Conversions The molar mass of a substance can be used as a conversion factor. The molar mass of a substance can be used as a conversion factor. Example - What is the mass in grams of 3.50 mol of the element copper, Cu? Example - What is the mass in grams of 3.50 mol of the element copper, Cu? Example – A chemist produced 11.9 g of Al. How many moles of aluminum were produced? Example – A chemist produced 11.9 g of Al. How many moles of aluminum were produced?

60. Conversion QUIZ For each of the following conversions, write two equalities that could be used as conversions facts. Show all work (use dimensional analysis). Give a final answer with correct units. How many moles of atoms are there in each of the following? 1) 5.87 g Ni 2) 2.25 x 10 25 atoms Zn 3) 150 g S 4) 50 atoms Ba

61. Conversions with Avogadro’s Number Avogadro’s number can be used as a conversion factor. Avogadro’s number can be used as a conversion factor. Example – How many moles of silver, Ag, are in 3.01 x 10 23 atoms of silver? Example – How many moles of silver, Ag, are in 3.01 x 10 23 atoms of silver? Example – What is the mass in grams of 1.20 x 10 8 atoms of copper, Cu? Example – What is the mass in grams of 1.20 x 10 8 atoms of copper, Cu?

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