Chemistry

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• Newton:

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Proposed a mechanical universe with small solid masses in motion

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• Dalton (1803)-

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all matter consists of tiny particles and elements characterized by mass of atom

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• Robert Brown (1827)

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provided first direct evidence of atoms

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• J.J. Thompson-

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“Plum Pudding” – electron suspended in positively charged field

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• Rutherford (1911)

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positive charge and most of mass contained in nucleus, electrons orbit around the nucleus

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• Bohr (1913)

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electrons orbit the nucleus in successive orbital shells based on energy levels; “quantized” shells. You usually look at Bohr’s model but Shrodinger made more indefinite model

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• Schrodinger (1926)

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“electron clouds” similar to shells, electrons travel in waves

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• Atomic Symbol

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o First letter always capitalized
o Second letter always lower case

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• Atomic Number

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# of protons in the nucleus
o # of protons = # of electrons; charges balance

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• Mass Number / Atomic Weight

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total number of p protons and neutrons (# of nucleons)

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Isotopes

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o Atoms whose nuclei have the same number of protons but different numbers of neutrons,; protons stay the same but neutrons are different; atomic mass
o Carbon-12 and Carbon-13
o Iron-55 and Iron-56 (p.296)
o Uranium-238

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Electrons and Orbitals

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o Bohr determined that an electron’s distance from the nucleus depended on its potential energy (book is wrong about filling orbitals)
o There are distinct energy levels called shells/ orbitals

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Electrons and Orbitals

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o Each shell/ orbital has a quantum number
o Shell 1 – n (quantum number)= 1
o Shell 2 – n= 2
o Shell 3 – n= 3
o Shell 4 – n= 4

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Electron Diagrams

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o REMEMBER - # of electrons is equal to the atomic numbers
o To figure out # in each shell use 2n2
n = the quantum number
o 1st shell = 2e- max.
o 2nd shell = 8e- max.
o 3rd shell = 18e- max.
o 4th shell = 32e- max.

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Subshells

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o Subdivisions within a shell
o S – can hold 2e-
o P – can hold 6e-
o D – can hold 10e-
o F – can hold 14e-

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Subshells

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o Subshells fill according to energy level (snake method
o Valance e-: the number of electrons in the outermost shell

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Organization of Periodic Table

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o Metals, Nonmetals, and Metalloids
o Metals: elements are luster, opaque, high density, and good conductors of electricity and heat
Malleable: can be hammered into shapes
Ductile: can be drawn into wires
o NonMetals: poor conductors of heat and electricity; can be transparent and are not malleable nor ductile
Solids, liquids and gasses
o Metalloids: have properties of metals and nonmetals, also called semiconductors

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Organization of Periodic Table (cont.)

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Period: horizontal row; 7 periods
o Properties gradually change across a period
o Size deceases from left to right (p. 300)
o All elements in same period have same atomic shells

Group (family): vertical column; 18 groups
o Properties within the family tend to be very similar
o Size increases from the top to bottom
o All elements in the same group have the same number of electrons in their outer shell (valence e-)

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Groups

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Group 1 – Alkali Metals
o 1 e- in outermost shell, many used for soaps, very reactive, may even explode in water
Group 2 – Alkaline- Earth Metals
o 2 e- in outermost shell, fire-resistant Group 3-12 – Transition Metals
o Less reactive with water than alkaline metals, used for structures, used in technology Group 16- Chalcogens
o 6 e- in outer shell, form ores
Group 17 – Halogens
o 7 e- in outer shell, form salts, often react with metals
Group 18 – Noble (Inert) Gasses
o 8 e- in outer shell, non-reactive gases

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Types of Chemical Reactions

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Synthesis
o Two or more simple compounds combine to form a more complicated one. These reactions come in the general form of:
o A + B ‡ AB
o One example of a synthesis reaction is the combination of iron and sulfur to form iron (ll) sulfide:
o 8 Fe + S8 ‡ 8 FeS
o In the cartoon, the skinny bird (reactant) and the worm (reactant) combine to make one product, a fat bird.

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Types of Chemical Reactions

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Decomposition
o Opposite of a synthesis reaction – a complex molecule breaks down to make simpler ones
o AB ‡ A + B
o One example of a decomposition reaction is the electrolysis of water to make oxygen and hydrogen gas:
o 2 H2O ‡ 2 H2 + O2
o In this cartoon the egg (reactant), which contained the turtle at one time, now has opened and the turtle (product) and egg shell (product) are now two separate substances

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Types of Chemical Reactions

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Single Displacement
o One element trades places with another element in a compound
o A + BC ‡ AC + B
o One example of a single displacement reaction is when magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas:
o Mg + 2 H2O ‡ Mg(OH)2 + H2

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Tyoes of Chemical Reactions

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Double Displacement
o Anions and cations of two different molecules switch places, forming two entirely different compounds
o AB + CD ‡ AD + CB
o One example of a double displacement reaction is the reaction of lead (ll) nitrate with potassium iodide to form lead (ll) iodide and potassium nitrate:
o Pb(NO3)2 + 2 Kl ‡ Pbl2 + 2 KNO3

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Types of Chemical Reactions

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Combustion
o Oxygen combines with another compound to form water and carbon dioxide. These reactions are exothermic, meaning the produce heat. An example of this kind of reaction is the burning of naphthalene.
o C10H8 + 12 O2 ‡ 10 CO2 + 4 H20