Models of the Atom a Historical Perspective

1. Models of the Atom a Historical Perspective

3. Early Models of the Atom • Throughout time, scientists have developed ideas about atoms. • The ideas have become more accurate over time. • For each scientist, you need to list their major contributions, or what made their model different from those that came before.

4. Democritus Early Greek Theories • 400 B.C. - All matter is made of indivisible particles called “atoms”. • Greek word “atomos” means not able to be divided. • Atom: the smallest unit of an element that maintains the properties of an element

5. John Dalton • 1800 - Dalton proposed a modern atomic model based on experimentation not on pure reason. • All matter is made of atoms, atoms are small particles, that cannot be created, divided, or destroyed. • Atoms of an element are identical. • Each element has different atoms. • Atoms of different elements combine in constant ratios to form compounds.

6. JJ Thomson (1897) • Atoms contain negatively charged particles called electrons. • Thought that the rest of the atom • must be positive. • Called the “Plum Pudding” model. (desert of choice at the time) • Electrons: negatively charged particles in an atom Adding Electrons to the Model

8. Zinc sulfide screen Thin gold foil Lead block Radioactive substance path of invisible -particles Ernest Rutherford (1909) • Did an experiment in which he shot alpha particles at gold foil. • Found that an atom is mostly empty space. • Found the dense, positively charged central region of the atom, called the nucleus. Nucleus in made up of protons and neutrons.

9. Relative size of the Atom (Page 548)

11. 1) Dalton’s “Billiard ball” model (1800-1900) Atoms are solid and indivisible. • Thompson “Plum pudding” model (1900) • Negative electrons in a positive framework. • The Rutherford model (around 1910) • Atoms are mostly empty space. • Negative electrons orbit a positive nucleus.

12. Bohr’s Model (1913) • Electrons are in specific paths called energy levels. • Electrons can move from one energy level to another. • The farther from the nucleus, the more energy the electrons have.

15. Presently • Electrons do not travel in definite paths, electrons path cannot be predicted. • Electron cloud: Region around the nucleus of an atom where electrons are likely to be found.

16. Parts of an Atom • There are 3 types of subatomic particles. • Protons: positive charge, found in nucleus • Neutrons: no charge, found in nucleus • Electrons: negative charge, found in electron clouds • Atomic mass unit: a unit of mass that describes the mass of an atom amu = .00000000000000000000000017 g • Proton: 1 amu • Neutron: 1 amu • Electron: 0 amu (1800 electrons to equal mass of 1 proton)

22. Subatomic Particle Chart

23. Atomic Number: The number of protons in an atom, also, the number of electrons. Example: lithium atomic number 3 will have 3 protons and 3 electrons Mass number: total number of protons and neutrons Example: lithium mass number 7 means 7 is the total number of protons and neutrons (3 protons and 4 neutrons) Atomic Number and Mass Number

35. Mass # p+ n0 e– Atomic # Ca 20 40 20 20 20 Ar 18 40 18 22 18 Br 35 80 35 45 35

36. Energy Level Capacity Chart

37. 3 p+ 4 n0 2e– 1e– Bohr - Rutherford diagrams • Putting all this together, we get B-R diagrams • To draw them you must know the # of protons, neutrons, and electrons. • Draw protons (p+), (n0) in circle (i.e. “nucleus”) • Draw electrons around in shells He Li Li shorthand 3 p+ 4 n0 2 p+ 2 n0 Draw Be, B, Al and shorthand diagrams for O, Na

38. Be B 4 p+ 5 n° 5 p+ 6 n° O Na 8 p+ 8 n° 11 p+ 12 n° 2e– 6e– 2e– 8e– 1e– Al 13 p+ 14 n°

39. Isotopes • Atoms of the same element that have different numbers of neutrons are called isotopes. • Due to isotopes, mass #s are not round #s. • H(1.00794) is made up of multiple hydrogens.

40. 3 p+ 3 n0 3 p+ 4 n0 2e– 1e– 2e– 1e– 6Li 7Li For more lessons, visit www.chalkbored.com

41. Periodic Table • Dmitri Medeleev • Discovered a pattern to the elements in 1869. • He wrote the names and properties of elements on cards, once he arranged the elements by atomic mass he realized a pattern. • Periodic: describes something that occurs or repeats at regualr intervals

43. Groups are Vertical Columns Elements in same group have similar chemical properties Elements in same group have same number of electrons in outer energy level Ex: Lithium, group one, one electron in outer energy level Periods are horizontal rows Elements in same period have different chemical properties. Elements in same period have different number of electrons in outer energy level. Elements in same period have same number of energy levels. Ex: lithium, period 2, 2 energy levels Using the Periodic Table “Groups and Periods”

44. Types of Elements • Nonmetals • 5 or more electrons in outer energy level • Right side of P.T. Metalloids elements that border the zig-zag line Metals • 3 or fewer electrons in outer energy level • Left side of P.T.

45. atomic Symbol

46. Ionic Compound Vocabulary Compound- 2 or more elements chemically joined Chemical Formula-combination of symbols and subscripts that shows what elements and how many atoms of each are in a compound, Example: Ionic Compound-compound that contains ionic bonds Ionic Bond-force of attraction between oppositely charged ions

47. Ionic Compound Vocabulary Octet Rule –chemical rule of thumb that states that atoms tend to combine in such a way that they each have eight electrons in their valence shells, giving them the same electronic configuration as a noble gas Valence Electron – an electron found in the outermost energy level Ion-charged particle that results from a neutral atom gaining or losing electrons Polyatomic ion- 2 or more atoms that combine and act like one ion

50. A. Naming ionic compounds made of a metal and nonmetal M-N • Name the metal 2. Name the nonmetal, add –ide ending *never use prefixes • NaCl • Sodium chloride • Li2O • Lithium oxide