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Chapter 2

Chapter 2. 2.1 Early History. Greeks 400 B.C. Aristotle : elements are earth, air, fire, and water Because he was a priest, everyone went with his idea over the scientists Democritus : used the word atomos to describe the small, indivisible particles Alchemists next 2000 years

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Chapter 2

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  1. Chapter 2

  2. 2.1 Early History • Greeks 400 B.C. • Aristotle: elements are earth, air, fire, and water • Because he was a priest, everyone went with his idea over the scientists • Democritus: used the word atomos to describe the small, indivisible particles • Alchemists next 2000 years • Some thought they could change cheap metals into gold • Others where more serious … discovered several elements, the method of distillation, and how to prepare mineral acids.

  3. 2.1 cont. • George Bauer 1500’s • metallurgy (extraction of metal from ores. • Paracelsus 1500’s • Medicinal chemistry • Robert Boyle 1600’s • Relationship between pressure and volume of air • George Stahl 16-1700’s • Phlogiston flows out of burning material (carbon dioxide) • Joseph Priestley 17-1800’s • “discovered’’ oxygen or dephlogisticated air • Karl Scheele first observed air

  4. 2.2 Chemical Laws • Conservation of Mass • Mass is neither created nor destroyed • Antoine Lavoisier (1700’s) • Named oxygen, oxygen • Father of Chemistry • He was a tax collector as well as a scientist… he was beheaded during the French Revolution • Law of Definite Proportion • A given compound always contains exactly the same proportion of elements by mass • Joseph Proust (17-1800’s)

  5. 2.2 cont. • Law of Multiple Proportions • When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 g of the first elements can be reduced to small whole numbers.

  6. 2.3 Dalton’s Atomic Theory • In the 1800’s Dalton came up with the following theory. • Each element is made up of tiny particles called atoms. • The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways. • Chemical compounds are formed when atoms of different elements combine with each other. A given compound always has the same relative numbers and types of atoms. • Chemical reactions involve reorganization of the atoms– changes in the way they are bound together. The atoms themselves are not changed in chemical reactions.

  7. 2.3 cont. • Dalton made the 1st periodic table based on atomic masses/ atomic weights. His elemental masses were later to be found off due to his previous assumptions about formulas. • Joseph Gay-Lussac and AmadeoAvagadro(17-1800’s) • Their work and hypothesis led to the determination of the absolute formulas

  8. 2.4 Early Experiments to Characterize the Atom • J. J. Thomson • Used cathode-ray tubes to discover electrons • He used the plum pudding model: electron resigns studded in positive pudding.

  9. 2.4 Cont. • Robert Millikan • Calculated the mass of an electron with the oil drop experiment. • Mass 9.11 x 10-³¹ kg • Becquerel • Noticed that a piece of uranium out of the Curie’s lab produced an image on a photographic plate while it was in the dark. He termed this spontaneous emission of radiation, radioactivity.

  10. 2.4 cont. • Ernest Rutherford • Used his gold foil experiment to discover the ‘nuclear’ atom. • Alpha particle (2+) used. If the plum pudding model were correct, the particles should pass through with some slight deviation. In reality, most particles passed through, but a few were bounced back towards the source admitter. • He came to the conclusion that the nucleus was positive due to the fact that the positive particles bounced back.

  11. 2.5 Modern Atomic Structure • An atom is made up of a very small nucleus containing protons and neutrons. This small nucleus gives the atom its mass. • Proton is a positive subatomic particle with a mass of 1.67 x10 -²⁷ kg • Neutron is neutral subatomic particle with a mass of 1.67 x10 -²⁷ kg

  12. 2.5 cont. • Of the three subatomic particles only the amount of protons stay the same to a particular element. • Carbon will always have 6 protons • If the amount of neutrons change, the result is an isotope. • A carbon atom with 6 neutrons is called carbon-12 • A carbon atom with 8 is called carbon-14 • If the amount of electrons differ from the amount of protons, the result is an ion. • Oxygen with 10 electrons has a -2 charge, called an oxide anion • Calcium with 19 electrons has a +1 charge, called a calcium cation.

  13. 2.5 cont. • Atomic Symbols • Atomic number also shown as a Z, gives the number of protons unique to that element. • Atomic Weight also shown as an A, gives the total number of protons and neutrons. • Charge comes from the difference in p+ and e-.

  14. 2.6 Molecules and Ions • Chemical bonds • There are two ways atoms can bond. • Covalent and Ionic bonds • Covalent bond is the sharing of electrons between atoms. • Molecule: a collection of atoms held together by covalent bonds.

  15. 2.6 • Ways to express a molecule • Chemical formula: symbols of the elements are used to express atoms present and subscripts to express ratios or amts of each • Structural formula: bonds are shown with lines connecting each elemental symbol, may or may not show shape and bond angles. • Space-filling model: shows relative size and relative orientation of each atom. • Ball and stick model: 3-d model with atoms as balls and bonds as sticks.

  16. 2.6 cont. • Ionic bonding is the force of attraction between to oppositely charged ions. The solid made is called an ionic solid or a salt. • Cations are the positive ions. • Anions are the negative ions. • Ex. Sodium and chlorine reacting to make sodium chloride.

  17. 2.7 Periodic Table • The current periodic table is arranged by… • Atomic number or number of protons. • Most elements are _______ and found on the left and middle of the table. • Metals: great conductors of heat and electricity, malleable (hammered into thin sheets), ductile (pulled into wires), lustrous/ shiny, and have a ‘sea of electrons’. Metals give electrons to form cations.

  18. 2.7 cont. • Those elements on the upper right side are called ________. With one exception, hydrogen. • Non-metal: gain electrons, are not great conductors of heat or electricity, are not malleable, ductile, or lustrous. • Horizontal lines on the table are called periods or rows. • Vertical lines are called families or groups.

  19. 2.7 cont. • Several Families have special names as they share similar chemical properties. • Alkali Metals are Group 1A metals (Li-Cs) that react violently with water and readily give up one e- …giving a +1 charge. • Alkali Earth Metals are Group 2A (Be-Ra) that readily give up two e- … giving a +2 charge. • Halogens are group 7A non-metals (F-At)that readily receive one e-…giving a -1 charge. • Noble gases or Inert gases are Group 8 metals that are ‘non-reactive’.

  20. 2.8 Naming • Type 1 or Binary ionic compounds • Contains one cation and one anion, written in that order. • The cation is always named first and the anion second. • Monatomic (one-atom) cation gets its from the element. • Ca+² … calcium Li+ … lithium • Monatomic anion takes root word from element and adds –ide. • Cl- …. chloride S-³ …sulfide

  21. 2.8 cont. • Binary Ionic Compounds (Type II) • When an element has more than one charged cation state (transition metals) names can tell one which charged ion is being used. • The use of roman numerals to depict charge. *most used. • Iron(II) or iron(III) • Higher charged cations are named with a –ic ending. • Cu+² is cupric ion • Lower charged cations are named with –ous • Cu+ is cuprous ion

  22. 2.8 cont. • Ionic with Polyatomic ions • Polyatomic ion names are MEMORIZED… • To name, just name PIs • Oxyanions … ions containing oxygen • With only two species • Suffix –ate denotes ion with larger number of O • Suffix –ite denotes ion with lower number of O • With more than 2 • Prefix hypo- denotes less than • Prefix per- denotes more

  23. 2.8 cont. • Binary Covalent Compounds (Type III) • Molecule formed between two non-metals • First element named first with full name • Second element named as if ion • Pre-fixes denote numbers of atoms (Memorize 1-10) • Mono pre-fix only used on second element.

  24. 2.8 cont. • Acids • A molecule with one or more hydrogen • Two ways to name • If acid does not contain oxygen, prefix is hydro- and the suffix is –ic. • EX. HF hydrofluoric acid • Contains oxygen, suffix will depend on name of anion • -ate becomes –ic “I ate it, and it was icky” • -ite becomes –ous

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