Chapter 17: Properties of Atoms and the Periodic Table

1. Table of Contents 17 Unit 4: The Nature of Matter Chapter 17: Properties of Atoms and the Periodic Table 17.1: Structure of the Atom 17.2: Masses of Atoms 17.3: The Periodic Table

2. Structure of the Atom 17.1 Scientific Shorthand • Scientists have developed their own shorthand for dealing with long, complicated names. • Chemical symbols consist of one capital letter or a capital letter plus one or two smaller letters.

3. Structure of the Atom 17.1 Scientific Shorthand • For some elements, the symbol is the first letter of the element's name. • For other elements, the symbol is the first letter of the name plus another letter from its name. • Because scientists worldwide use this system, everyone understands what the symbols mean.

4. Structure of the Atom 17.1 Atomic Components • An element is matter that is composed of one type of atom, which is the smallest piece of matter that still retains the property of the element. • Atoms are composed of particles called protons, neutrons, and electrons. Click image to view movie

5. Structure of the Atom 17.1 Atomic Components • Protons and neutrons are found in a small positively charged center of the atom called the nucleusthat is surrounded by a cloud containing electrons. • Protons are particles with an electrical charge of 1+.

6. Structure of the Atom 17.1 Atomic Components • Electrons are particles with an electrical charge of 1–. • Neutrons are neutral particles that do not have an electrical charge.

7. Structure of the Atom 17.1 Quarks—Even Smaller Particles • Protons and neutrons are made up of smaller particles called quarks. • So far, scientists have confirmed the existence of six uniquely different quarks.

8. Structure of the Atom 17.1 Quarks—Even Smaller Particles • Scientists theorize that an arrangement of three quarks held together with the strong nuclear force produces a proton. • Another arrangement of three quarks produces a neutron

9. Structure of the Atom 17.1 Finding Quarks • To study quarks, scientists accelerate charge particles to tremendous speeds and then force them to collide with—or smash into—protons. This collision causes the proton to break apart. • The particles that result from the collision can be detected by various collection devises.

10. Structure of the Atom 17.1 Models—Tools for Scientists • Scientists and engineers use models to represent things that are difficult to visualize—or picture in your mind. • Scaled-down models allow you to see either something too large to see all at once, or something that has not been built yet. • Scaled-up models are often used to visualize things that are too small to see.

11. “Atomic Structure”

12. Different Models of the atom Greek Model Dalton’s Atomic Theory Thomson’s Model Rutherford’s Atomic Theory Bohr’s Model of the Atom Electron Cloud Model Studying Atoms

13. Structure of the Atom 17.1 Models—Tools for Scientists • To study the atom, scientists have developed scaled-up models that they can use to visualize how the atom is constructed. • For the model to be useful, it must support all of the information that is known about matter and the behavior of atoms.

14. Aristotle thought that all substances were built up from only 4 elements Earth Air Fire Water These elements were a combination of 4 qualities hot, cold, dry, and wet Aristotle

15. ~ ~ Fire Water Earth Air The Hellenic Market

16. Aristotle

17. Aristotle did not think there was a limit to the number of times matter could be divided. For centuries people believed this model. Aristotle

18. The Greek philosopher Democritus (460 B.C. – 370 B.C.) was among the first to suggest the existence of atoms (from the Greek word “atomos”) ATOM He believed that atoms were indivisible and indestructible His ideas did agree with later scientific theory, but did not explain chemical behavior, and was not based on the scientific method– but just philosophy Defining the Atom

19. Greek Model “To understand the very large, we must understand the very small.” Democritus • Greek philosopher • Idea of ‘democracy’ • Idea of ‘atomos’ • Atomos = ‘indivisible’ • ‘Atom’ is derived • No experiments to support idea • Continuous vs. discontinuous theory of matter Democritus’s model of atom No protons, electrons, or neutrons Solid and INDESTRUCTABLE

20. Who Was Right? • Greek society was slave based • Beneath famous to work with hands • did not experiment • Greeks settled disagreements by argument • Aristotle was more famous • He won! • His ideas carried through middle ages. • Alchemists change lead to gold California WEB

21. John Dalton

22. John Dalton (1766-1844) was known as the “Father of the modern atom.” He was the first to actually test, previously the Greeks would just theorize. In his work he developed Dalton's Atomic Theory. John Dalton

23. Structure of the Atom 17.1 The Changing Atomic Model • In the 1800s, John Dalton, an English scientist, was able to offer proof that atoms exist. Because Dalton’s atomic theory was proven through many experiments His THEORY became widely accepted.

24. Dalton’s Atomic Theory (experiment based) All elements are composed of tiny indivisible particles calledatoms Atoms of the same element are identical. Atoms Can’t be Created nor Destroyed! John Dalton (1766 – 1844) 4) Atoms of different elements combine in simple whole-number ratios to form chemical compounds 5) In a particular compound, atoms of different elements always combine in the same way 6) Allatoms of the same element have the same mass, atoms of diff. elements have diff. masses

25. The Elements are pictured as solid spheres: Each type of atom is represented by a tiny, solid sphere with a different mass. Dalton’s Model

26. Dalton’s Elements John Dalton 1808

27. JJ Thomson

28. J.J. used the idea behind charges: -- Like charges repel -- Unlike charges attract With this idea in mind, J.J. used electric current to study the atom.  Remember my ex: with the Magnets JJ. Thomson

29. magnet voltage source William Crookes - + vacuum tube metal disks Crooke’s Tube

30. Discovery of the Electron Looking at what JJ saw, what do you think he determined was the charge on the particles in the beam?

31. + - Thomson’s Experiment voltage source ON - OFF + By adding an electric field… he found that the moving pieces werenegative.

32. In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle: the electron  The Electron was named by G. Johnstone Stoney ! ** Thomsons experiments were the 1st proof that atoms are made of smaller particles.

33. Mass of the Electron Mass of the electron is 9.11 x 10-28 g The oil drop apparatus 1916 – Robert Millikan determines the mass of the electron: 1/1840 the mass of a hydrogen atom; has one unit of negative charge

34. Conclusions from the Study of the Electron: Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons. Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons Electrons have so little mass that atoms must contain other particles that account for most of the mass

35. Some Modern Cathode Ray Tubes • Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

36. J.J. reasoned that if the atom had negative little particles inside it, but was considered to be NEUTRAL, then there must also be some positive particles too. J.J. Thomson

37. Thomson’s Atomic Model J. J. Thomson Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

38. Conclusions from the Study of the Electron: • Eugen Goldstein in 1886 observed what is now called the “proton” - particles with a positive charge, and a relative mass of 1 (or 1840 times that of an electron) • 1932 – James Chadwick confirmed the existence of the “neutron” – a particle with no charge, but a mass nearly equal to a proton

39. Rutherford’s Atomic Theory

40. Ernest Rutherford (1871-1937) • Learned physics in J.J. Thomson’ lab. • Noticed that ‘alpha’ particles were sometime deflected by something in the air. • Gold-foil experiment

41. Ernest Rutherford’sGold Foil Experiment - 1911 • Alpha particles are helium nuclei - The alpha particles were fired at a thin sheet of gold foil • Particle that hit on the detecting screen (film) are recorded

42. Lead collimator Gold foil a particle source q Rutherford ‘Scattering’ • In 1909 Rutherford undertook a series of experiments • He fired a (alpha) particles at a very thin sample of gold foil • According to the Thomson model the a particles should only • be slightly deflected • 4. Rutherford discovered that they were deflected through large angles and could even be reflected straight back to the source

43. Rutherford’s problem: In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target? Target #2 Target #1

44. The Answers: Target #2 Target #1

45. Rutherford’s Findings • Most of the particles passed right through • A few particles were deflected • VERY FEW were greatly deflected “Like howitzer shells bouncing off of tissue paper!” Conclusions: The nucleus is small The nucleus is dense The nucleus is positively charged

46. 152 mm howitzer-gun M1937

47. The Rutherford Atomic Model • Based on his experimental evidence: • The atom is mostly empty space • All thepositive charge, and almost all the mass is concentrated in a small area in the center. He called this a“nucleus”

48. Thenucleusis composed ofprotons and neutrons The electrons distributed around the nucleus, and occupy most of the volume His model was called a“nuclear model” The Rutherford Atomic Model

49. Bohr’s Model of the Atom

50. Niels Bohr • In the Bohr Model (1913) the neutrons and protons occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun. • They are not confined to a planar orbit like the planets are.