Classifying Matter and the Periodic Table From Chapter 8 & 10 in Trefil & Hazen The Sciences
…discuss the origin and development of the idea of “atoms”. • 530 B.C. Democritus • atomos • Smallest piece of “uncuttable” matter • atoms are eternal and unchanging • relationship between atoms is constantly shifting
Figure 8-1 Repeatedly dividing a bar of gold, just like cutting paper repeatedly, produces smaller and smaller groups of atoms, until you come to a single gold atom. Dividing that atom into two parts produces fragments that no longer have the properties of gold.
AntoineLavoisier’s law of conservation of matter • measured the mass of substances before and after chemical reactions • found that the masses were always equal
Joseph Proust’ law of constant composition: • he found that a given compound always contains the same elements in the same proportions by mass
Dalton’s atomic theory of matter • each element is composed of extremely small particles called atoms • all atoms of a given element are identical, but they differ from those of other any other element
Dalton’s atomic theory of matter • a given compound always has the same relative numbers and kinds of atoms • atoms are neither created nor destroyed in any chemical reaction
…distinguish between atoms and elements. • Atom = the smallest particle of an element that retains the chemical identity of that element. • An element is a material made from a single type of atom.
…evaluate evidence for the existence of atoms. • Behavior of a gas • Chemical combinations • Radioactivity • Brownian motion • X-ray crystallography • Atomic-scale microscopy
Thompson’s Tube gave first evidence of the electron • “cathode” is the connection to negative source of electricity • The “ray” was a stream of particles carrying negative electric charge
Interpret E. Rutherford’s gold foil experiment. Figure 8-3 In Rutherford’s experiment, a beam of radioactive particles was scattered by atomic nuclei in a piece of gold foil. A lead shield protected researchers from the radiation.
Discovery of the electron • Discovery of the proton • Discovery of the neutron 3 Li 6.941
Figure 8-6 Stairs provide an analogy to energy changes associated with electrons in the Bohr atom.
Figure 8-7 Electrons may jump between the energy levels shown in (a) and, in the process, (b) absorb or (c) emit energy in the form of a photon.
Physical Properties… • describe the physical characteristics of a substance, such as color, hardness, density, texture, and phase.
Physical change… • is a change in some property of a substance. • Usually occur during heating/cooling or when there is a change in pressure.
Chemical properties… • characterize the tendency of a substance to transform into a different substance.
Chemical change • Atoms rearrange during a chemical change, switching partners as previous connections are broken and new ones are formed. • Evidence?
Physical change New attributes result from new set of conditions imposed on the material Chemical change New attributes are the physical properties of a fundamentally different material
Element: a pure substance containing only one kind of atom • Periodic Table – front cover and p 172 • Element symbol Latin name • Sodium Na natrium • Potassium K kalium • Copper Cu cuprum • Gold Au aurum • Lead Pb plumbum
Atoms that compose an element may combine in a variety of ways. • Gold, Au • Sulfur, S8 • Nitrogen, N2 • Oxygen, O2
Compounds –atoms of different elements combined in a fixed ratio • Compounds have physical and chemical properties different from the properties of their elemental components • NaCl, sodium chloride or table salt • Fe2O3, iron oxide or rust
Mixtures = various combinations of elements, compounds, or both • Stainless steel is a mixture of the elements iron, chromium, nickel and carbon. • Our atmosphere is a mixture of nitrogen, oxygen, argon, carbon dioxide, water vapor, and pollutants.
How might we separate the following: • Iron filings and sand • Sawdust and rubber washers • Salt and water • Oil and water • Point: Components of any mixture can be separated by physical means.
Element Gold, Au Hydrogen, H2 Silicon, Si Compound Salt, NaCl Carbon Dioxide, CO2 Ammonia, NH3 Pure Substance
Heterogenous Mixture Sand in water Oil and water Salt and pepper Homogenous Mixture Solution Suspension Impure Substances
Solution Air (N2, O2) Salt water (NaCl, H2O) Stainless Steel (Fe, Cr, Ni, C) Suspension Milk (water, solid proteins) Blood (water, solid cells, nutrients) Fog (air, tiny water droplets) Homogenous Mixture
Periodic Table Basics: Element Symbol, Atomic Number, Average Atomic Mass, Families and Periods. Figure 8-13 The periodic table of the elements. The weights of the elements increase from left to right. Each vertical column groups elements with similar chemical properties.
Average Atomic Mass = sum of protons and neutrons; an average of the relative abundance of the isotopes for that element 92 U 238.028
…compare and contrast families of elements in terms of their chemical properties.Alkali Metals, group IA (1)
…compare and contrast families of elements in terms of their chemical properties.Alkaline Earth Metals, group IIA (2)
…compare and contrast families of elements in terms of their chemical properties.Halogens, group VIIA (17)
…compare and contrast families of elements in terms of their chemical properties.Noble Gases, group VIIIA (18)
Text questions: • Chapter 8 • Discussion Questions 6-10 p. 175 • Chapter 10 • Discussion Questions p. 216: 1,2,4,5,6,7,11 and Problems 1, 2, 3.