Classifying Matter and the Periodic Table From Chapter 8 & 10 in Trefil & Hazen The Sciences

Classification of Matter

…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.

Antoine Lavoisier’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

Mendeleev and the Periodic Table of the Elements

Mendeleev’s Table

…interpret J.J. Thompson’s cathode ray tube experiment.

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

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. Interpret E. Rutherford’s gold foil experiment.

Discovery of the electron electron Discovery of the proton proton Discovery of the neutron neutron 3 Li 6.941

“Flame Test”

Bohr Model of the Atom

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 ElementsymbolLatin name SodiumNanatrium PotassiumKkalium CopperCucuprum GoldAuaurum LeadPbplumbum

Atoms that compose an element may combine in a variety of ways. Gold, Au Sulfur, S 8 Nitrogen, N 2 Oxygen, O 2

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 Fe 2 O 3, 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.

Classification of Matter

Pure Substance Element –Gold, Au –Hydrogen, H 2 –Silicon, Si Compound –Salt, NaCl –Carbon Dioxide, CO 2 –Ammonia, NH 3

Impure Substances Heterogenous Mixture –Sand in water –Oil and water –Salt and pepper Homogenous Mixture –Solution –Suspension

Homogenous Mixture Solution –Air (N 2, O 2 ) –Salt water (NaCl, H 2 O) –Stainless Steel (Fe, Cr, Ni, C) Suspension –Milk (water, solid proteins) –Blood (water, solid cells, nutrients) –Fog (air, tiny water droplets)

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. Periodic Table Basics: Element Symbol, Atomic Number, Average Atomic Mass, Families and Periods.

Average Atomic Mass = sum of protons and neutrons; an average of the relative abundance of the isotopes for that element 92 U

…distinguish between properties of metals, metalloids, and nonmetals.

…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)

NaCl CaCl 2 MgO Al 2 O 3

H 2 O CO 2 CH 4 NH 3

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.