The Structure of the Atom

1. The Structure of the Atom Chapter 5 (page 132)

2. Essential Question!! • How does the atomic structure of an atom aid us in explaining physical properties, chemical properties, and bond strengths??

3. Vocabulary: Section1 • Nucleus • Atomic number • Isotopes • Mass number • Atomic mass unit • Radioactivity • Decay • Ion

4. What we’ve seen so far… - Chemistry is about discovering and understanding natural laws using the scientific method - Energy cannot be created nor destroyed Chapter 1 The Science of Chemistry

5. What we’ve seen so far… - Matter can be mixtures or substances. The smallest unit of a pure substance is an element. - Each element is a type of atom, and they can be arranged in a periodic table. -Atoms come together to form compounds. Atoms with an electric charge are known as ions. Chapter 1 The Science of Chemistry Chapter 2 Matter and Atoms

6. What we’ve seen so far… Chapter 1 The Science of Chemistry Chapter 2 Matter and Atoms Chapter 3 Temperature, Energy, and Heat - Temperature is a measure of kinetic energy. - Heat is thermal energy. - Heat gain and heat loss can cause phase changes, as molecules are rearranged.

7. What we’ve seen so far… Chapter 1 The Science of Chemistry Chapter 2 Matter and Atoms Chapter 3 Temperature, Energy, and Heat Chapter 4 Physical and Chemical Change - In a physical change molecules are rearranged. In a chemical change atoms are rearranged to make new substances. - Chemical reactions can be endothermic or exothermic. - Many reactions occur in aqueous solution, and some elements are more reactive than others.

8. Answers can be found inside the atom Chapter 1 The Science of Chemistry Chapter 2 Matter and Atoms Chapter 3 Temperature, Energy, and Heat Chapter 4 Physical and Chemical Change How can we explain the properties and behaviors observed so far?

9. 92 different types of atoms!

10. Atoms are made from smaller particles! protons neutrons electrons Each of the elements is a unique type of atom.

11. It started a long time ago… 460 – 370 BC Today Democritus Beginning of Atomism You cannot divide something in half forever. The smallest piece of matter is called an atom.

12. Dalton’s Postulates 1808 Today 460 – 370 BC 1.All elements are made of tiny indivisible particles called atoms. Democritus Atomism 2. All atoms of the same element are the same, but different from atoms of every other element. Over 2,000 years later John Dalton comes up with the first “modern” atomic theory. 3.Chemical reactions rearrange atoms but do not create, destroy, or convert atoms from one element to another. 4. Compounds are made from combining atoms in simple whole number ratios.

13. Another kind of light? Today 1870 460 – 370 BC 1808 Democritus Atomism Dalton “Modern” atomic theory William Crookes invents a tube in which virtually all the gas has been removed. Under high voltage, a ray was emitted from the cathode end of the tube.

14. It started a long time ago… 1897 Today 460 – 370 BC 1808 1870 Democritus Atomism Crookes Cathode rays Dalton “Modern” atomic theory J.J. Thomson discovers the electron Cathode rays must be negative.

15. It started a long time ago… 1910 Today 460 – 370 BC 1808 1897 1870 Democritus Atomism Crookes Cathode rays Thomson Discovery of the electron Dalton “Modern” atomic theory Ernest Rutherford discovers the nucleus

16. Size and mass The size of the atom comes mostly from the space occupied by the electrons The mass of the atom comes mostly from the nucleus

17. Scientists believed that substances were made up of one big piece of mater, however they realized that is matter was broken in half, over and over again, you would get to the point where it could not be broken anymore and still have the same properties . • That smallest unit was called an atom or a compound. • When you put high voltage electricity through a gas, you can get light. • Different elements have different colors • Scientists found out that if you were to run high-voltage electricity through a gas, you could get a different color. • And if you were to run that light through a special lens, called a diffraction grating, it will break the light up into its individual color • Each element and compound produces a special unique line spectra. • The amount of lines seen in a line spectra is related to the amount of electrons the atom has.

18. There are 92 naturally occurring elements on the periodic table, however all matter is made up of those 92 elements. • Scientists later found out that atoms could be broken down into three smaller units: protons: positive charge electrons: negative charge • and neutrons: no charge/ neutral • The protons are the same as the atomic number and the amount of electrons in an atom • The neutrons have no charge • Protons and neutrons are found in the nucleus of an atom and make up 99.97% of the weight in an atom • The electrons are found in the cloud around the nucleus and make up 0.03% of the weight of the atom • Elements are special atoms that have the same number of protons inside the nucleus. Elements that are the same have the same physical properties.

19. About 2,000 years ago a Greek philosopher names Democritus was the first to say that the matter was made up of all small units called atoms. • But for 2,000 years nobody could prove or disprove his theory due to scientific differences. In 1808, john Dalton came up with four postulates:1. All elements are made up of tiny invisible particles called atoms2. All atoms of the same element are alike but different from atoms of every other element.3. Chemical reactions rearrange atoms but do not create, destroy or convert from one element to another.4. Compounds are made from combining atoms in simple whole number ratios. • In the mid 1800’s, William Crookes invented a machine that ran high voltage through an almost vacuum tube ( a cathode ray tube)

20. In 1887 J.J. Thompson was able to resolve the questions about the particles found in the atom using a cathode ray tube • Thompson deduced that cathode rays must be negative and that if atoms had a negative charge, then there must also be a positive charge to cancel out the negative charge

21. Cathode Ray Tube

22. Cathode Rays and Electrons • 1. Different gases glow with different colors • 2. The glass around the cathode glows • 3. Objects placed in the path cause shadows-- (Maltese cross)

23. Cathode Rays and Electrons • 4. A movable wheel will roll when placed in the path. • 5. Cathode rays are deflected by magnetic fields (like electric currents) • 6. The rays are deflected away from the negative electrode.

24. Cathode Ray and Electron Conclusion • Electrons are negatively charged particles. • Because atoms are neutral and they contain electrons, there must also be something positive on the atom • Because electrons have such a little weight there must be something in the atom that makes up the weight

25. Assignment Take a new sheet of paper and fold it into three sections Write your name, the title of the chapter and the number On the first section from the sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

26. Thompson’s discovery stunned the scientific world • He found out that cathode rays, 2000 times smaller than the proton, were smaller than the atom • He called the new particles electrons and he proposed that electrons were in all atoms

27. In 1910 Earnest Rutherford designed and carried out crucial experiments that provided answers to where the positive charges of an atom was found • Marie and Pierre had discovered that uranium was radioactive and released energetic alpha particles (positively charged protons) that were 2000 times heaver than the mass of electrons • Rutherford designed an experiment that would shoot alpha particles through a thin sheet of gold foil and observe what happened • He expected most of the particles to be deflected a little as they went through • What he saw was that most went through and a few were deflected and 1 out of every 20,000 reversed in direction bouncing back from the foil

28. Rutherford’s Gold Leaf Experiment

29. Gold leaf experiment at atomic level

30. Conclusion: Atomic particles • Proved that there was a dense nucleus, but it was small • Nucleus . protons & usually neutrons • Atom . Electrons in electron cloud

31. Forces in an atom: • nuclear forces • . proton-proton • . proton-neutron • . neutron-neutron • Short range forces

32. Charges in the atom

33. 6 protons in carbon 7 protons in nitrogen 8 protons in oxygen You obtain a different element! The number of protons is also called the atomic number for that element.

34. 8 protons A negative oxygen ion O2- Two electrons are not neutralized by protons, making this a –2 charged atom Two extra electrons

35. Isotope • Atoms of the same element that have different masses • Same number of protons • Different number of neutrons

36. Isotopes of Hydrogen Protium • . 1 proton, 0 neutron,1 electron Deuterium • . 1 proton, 1 neutron, 1 electron Tritium • . 1 proton, 2 neutrons, 1 electron

37. Assignment On the second section of that sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

39. Carbon-12 Carbon-13 Carbon-14 Name Mass number # protons # neutrons

40. Atomic Mass of Subatomic Particles • electron 0.000548 u • proton 1.007276 u • neutron 1.008665 u

41. Average Atomic Masses • Average is determined by • multiplying decimal equiv. of % by the atomic mass of each isotope. • percentage * atomic mass • 69.17 % and 30.83 % substance. • .6917 * 62.939598 u + 0.3083 * 64.927793 u = 63.55 u

42. Atomic mass • The atomic mass is the relative atomic mass of an atom • review • C-12 = 12.0000 u • 1 carbon 12 atom has an atomic mass of 12.0000 u • The masses on the Periodic table are the AVERAGE ATOMIC MASSES

43. Isotope periodic table (first 4 rows)

44. Assignment • Review the BFW • Answer questions # 1-3 on page 162 • Write a three dollar paragraph summary of this section (based on what you learned) • Turn in completed work • Honors Chemistry Homework: page 163 # 23 - 28

45. Vocabulary: Section 2 • Quantum theory • Quantum state • Frequency • Wavelength • Plank’s constant • Photon • Orbital • Energy level • Pauli exclusion principle

46. Why is the periodic table shaped this way? 2 elements 8 elements 8 elements 18 elements Why is it not shaped like a “box”?

47. Elements in the same column have similar chemical properties. The periodic table Li+ Na+ K+ They tend to donate 1 electron.

48. Elements in the same column have similar chemical properties. The periodic table F– Cl– Br– They tend to accept 1 electron.

49. Elements in the same column have similar chemical properties. The periodic table Never in ionic form They do not donate or accept electrons.

50. Elements in the same column have similar chemical properties. Electrons are responsible for these chemical properties. Quantum theory explains how the universe behaves on a very small scale. Niels Bohr