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Chapter 3

Chapter 3 . Discovering the Atom. Essential Questions. How was the idea of the atom developed historically? What important experiments were performed to change our view of atoms? What are Subatomic Particles? What is the Modern View of the atom? What is Atomic Mass?.

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Chapter 3

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  1. Chapter 3 Discovering the Atom

  2. Essential Questions • How was the idea of the atom developed historically? • What important experiments were performed to change our view of atoms? • What are Subatomic Particles? • What is the Modern View of the atom? • What is Atomic Mass?

  3. Historical View – The 4 Elements

  4. Democritus’ Atoms

  5. Changes in The Way We View Matter • The ___________view of __________was based on __________and not on ______________data. • In 1661, _____________published a proposal that a substance was not an ___________if it was made of two or more _________________.

  6. Changes in The Way We View Matter • 1760’s - _____________defines the compound.

  7. Experiments That Changed The Way We View Matter • The Law of ____________of __________.(1774)

  8. Dalton’s Atomic Theory • Elements are made of _______particles called __________. • All _________of a given element are ___________. • The _________of a given element are ___________from those of any other __________.

  9. Dalton’s Atomic Theory • Atoms of _____element can combine with atoms of _______elements to form _____________. A given __________always has the _______relative _________and ________of atoms.

  10. Dalton’s Atomic Theory • Atoms are ____________in _______processes. That is, atoms are not _________or __________in chemical reactions. A chemical reaction simply __________the way the atoms are ___________together.

  11. Law of Constant Composition • IFA given __________always has the _______relative ______and _____of atoms, • THEN a given _________always ______the _______proportion (by _____) of the elements.

  12. An Example • Water always contains ____times as much oxygen (by mass) as hydrogen. • 9 grams of water contains ____grams of oxygen and ___gram of hydrogen. • 27 g of water has _____g of oxygen and ___g of hydrogen. • What about 100 g of water?

  13. From the other direction • 8.00 g of oxygen will react with 1.00 g of hydrogen to form ______g of water. • If you mix 24 g of oxygen with 6 g of hydrogen and react them, how much water can you form?

  14. Lab on Constant Composition • Potassium chlorate contains 31.9% potassium, 29.0 % chlorine, and 39.2% oxygen (by mass). • This should be _____for all samples of _____potassium chlorate.

  15. Lab on Constant Composition • If you heat potassium ________you get potassium _______and _______: 2 KC1O3 → 2 KCl+ 3 O2 • We will carry out this _____________and measure how much _______we gave off (by difference).

  16. Review of Chemical Formulas • Each atom present is represented by its _________symbol. • The _________of each type of atom is indicated by a ____________written to the right of the element symbol. • When only _______atom of an element is present, the subscript ____is not written.

  17. Some Formulas • KClO3 • H2O • CH4 • C12H22O11 • S8

  18. The Structure of the Atom • Until the work of ______________, scientists believed that atoms were the _________possible ___________. • Cathode ray tube – led to the ___________of the ___________by _____________.

  19. Plum Pudding

  20. Rutherford’s Experiment

  21. MODERN ATOMIC STRUCTURE The _____________charge is found in the nucleus. Therefore, _____________are located in the nucleus. The number of __________held by the nucleus is called ATOMIC _______. _____________move about the ____________and account for most of the _____________of the atom.

  22. DISCOVERING NEW FORMS OF HYDROGEN In the early 1930’s, a new form of hydrogen was discovered. It accounted for 0.015% of all hydrogen in nature. The only difference was that it was twice as heavy as the most common form of hydrogen(99.985%). It was, therefore, called heavy hydrogen. Atomic # Atomic Mass# of p# of e H Heavy H Why is heavy hydrogen twice as heavy?

  23. A NEW SUB-ATOMIC PARTICLE In 1935, an English scientist of the name ___________discovered a new particle. Its characteristics were: a. Its mass was basically the _________as that of the ______. b. Its charge was ____________. ______________, therefore, called this a _____________.

  24. ISOTOPES Apparently, ___________hydrogen contains a ___________making it twice as ______________. Mass Number = the sum of the number of ___________and ____________or sum of _____________. Isotopes – atoms of the _________element that have the _______number of ___________, but a different number of ___________. – have the same atomic __________, but different ________ number Neutrons = ________Number – Atomic ___________

  25. ISOTOPES CONTINUED At.#Mass ##p#e#n 32He 42He 168O 178O 188O

  26. ATOMIC MASS This is the relative mass of an ________based, temporarily, on _____________as exactly 1. Hydrogen Chloride – 2.74% H and 97.3%Cl Water – 11.1%H and 88.9%O Ammonia – 17.6%H and 82.4%N Salt – 39.3%Na and 60.7%Cl

  27. ATOMIC MASSES Old system: H-1 = 1.0000….. C-12 = 11.9987 New system: C-12 = 12.00000…… H-1 = 1.007825 So atomic mass is defined as the __________mass of an atom based on __-12 as exactly _____.

  28. AVERAGE ATOMIC MASS %PRESENTATOMIC MASS H-1 99.985% 1.007825 H-2 0.015% 2.01410 Ave. Atomic Mass = 1.00797 TEXT BOOK ATOMIC MASS This is the the average of the atomic masses of the isotopes of an element based on C-12 as exactly 12

  29. CALCULATING ATOMIC MASSES % PRESENTATOMIC MASS Cl-35 75.77% 34.969 Cl-37 24.23% 36.966 Ave. Atomic Mass = ? C-12. 98.892% 12.0000… C-13 1.108% 13.00335 Ave. Atomic Mass = ?

  30. Subatomic Particles • _______________-- are subatomic particles that comprise known matter and anti-matter. • ______________--Do not help hold an atom’s nucleus together and are found in known matter. • Are neutrinos and electrons • _______________ • Particles such as the proton or neutron.

  31. Quarks • Quarks--Does not help hold an atom’s nucleus together. • Quarks are extremely ___________, • classified by the _________and _________of charge that they hold, • are the most ______________particles discovered to date.

  32. Bosons and Leptons and QUARKS – Oh MY! TYPES OF QUARKS • Up +2/3 • Down -1/3 • Top (aka Truth) • Bottom (aka Beauty) • Charm (aka Charmed) • Strange (aka Strangeness) Proton – 2 Ups and 1 down, 2(2/3) + (-1/3) Neutron – 1 Up and 2 Downs, (2/3) + 2(-1/3)

  33. Atomic Masses and the Law Of Constant Composition • Remember that the Law of Constant Composition states “a given compound always contains the same proportion (by mass) of the elements.” • This now makes perfect sense with what we know about relative masses.

  34. Water • Oxygen has an relative mass of ______ compared to hydrogen’s _____. • ______grams of oxygen has as many O atoms as ______ grams of hydrogen has H atoms. • ____ grams of hydrogen has twice as many H atoms as _______ grams of oxygen has O atoms. • The mass ratio in water (H2O) is ___:__ or ___:___

  35. Mass Ratios • Carbon and hydrogen react in a ___:____ mass ratio to form methane (CH4). • How many grams of carbon would react with 6.0 grams of hydrogen? • 18 g • How does this relate to Atomic Masses?

  36. AlH3 • What is the mass ratio for AlH3? • Al = __________, H = _____Therefore mass ratio = __________/__ or ___:___ • How many grams of hydrogen would react with 18 grams of aluminum? • 2 g • How many grams of AlH3 would form from the reaction of 18 grams of aluminum and 6 grams of hydrogen? • 20 g

  37. PERIODIC TABLE The elements are arranged in the Periodic Table in order of increasing ______ __________. When elements are arranged this way, the chemical and physical properties re-occur in a __________fashion. (Dimitri Mendeleev) Horizontal Rows – ___________ Vertical Columns – ___________

  38. Periodic Law • When the elements are arranged in order of increasing __________ ___________ there is a periodic repetition of their chemical and physical properties. • The chemical and physical properties of the elements are a _________function of the _________ _____________.

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