Chapter 2
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Transcript of Chapter 2
Chapter 2
Atoms, Molecules, and Ions
HistoryHistory
GreeksGreeks Democritus and Leucippus – atomos Democritus and Leucippus – atomos
(meaning indivisible or uncuttable) (meaning indivisible or uncuttable) Aristotle- elementsAristotle- elements Alchemy (a Alchemy (a phase in the development
of modern chemistry) English schoolteacher, John Dalton English schoolteacher, John Dalton
linked the idea of elements with the linked the idea of elements with the idea of atoms. 1803-1807idea of atoms. 1803-1807
Dalton’s Atomic TheoryDalton’s Atomic Theory
1. Elements are made up of atoms1. Elements are made up of atoms 2. Atoms of each element are identical. 2. Atoms of each element are identical.
Atoms of different elements are different.Atoms of different elements are different. 3. Compounds are formed when atoms 3. Compounds are formed when atoms
combine. Each compound has a specific combine. Each compound has a specific number and kinds of atom.number and kinds of atom.
4. Chemical reactions are rearrangement 4. Chemical reactions are rearrangement of atoms. Atoms are not created or of atoms. Atoms are not created or destroyed.destroyed.
Laws
Conservation of Mass Law of Definite Proportion-
compounds have a constant composition by mass.
They react in specific ratios by mass.
Experiments to determine what an atom was
J. J. Thomson- used Cathode ray tubes Thomson’s experiment (1897) is
generally accepted as the discovery of the electron.
Thomson’s ExperimentVoltage source
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Thomson’s ExperimentVoltage source
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Thomson’s ExperimentThomson’s ExperimentVoltage source
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Passing an electric current makes a beam appear to move from the negative to the positive end
Thomson’s ExperimentThomson’s ExperimentVoltage source
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Passing an electric current makes a beam appear to move from the negative to the positive end
Thomson’s ExperimentThomson’s ExperimentVoltage source
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Passing an electric current makes a beam appear to move from the negative to the positive end
Thomson’s ExperimentThomson’s ExperimentVoltage source
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Passing an electric current makes a beam appear to move from the negative to the positive end
Thomson’s ExperimentThomson’s ExperimentVoltage source
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Voltage source
Thomson’s Experiment
By adding an electric field
Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electric field
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Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electric field
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Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electric field
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Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electric field
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Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electric field
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Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electric field he found that the moving pieces were negative
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Thomsom’s Model
Found the electron Couldn’t find
positive (for a while)
Said the atom was like plum pudding
A bunch of positive stuff, with the electrons able to be removed
RadioactivityDiscovered by accident by Henri BequerelThree types alpha- do not travel very far, do not pass through anything thick (less than 1in), can be very damaging when inside the body, but outside particles won’t even go through the skinbeta- high speed electron, can travel up to six feet from source, like alpha more damaging inside the human body than outsideGamma (x rays)- high energy light (photons), travel the speed of light, have greater penetrating power than alpha or beta, gamma rays come from the nucleus while x rays come from electron shells,
Rutherford’s Experiment
Used uranium to produce alpha particles
Aimed alpha particles at gold foil by drilling hole in lead block
Since the mass is evenly distributed in gold atoms alpha particles should go straight through.
Used gold foil because it could be made thin
Lead block
Uranium
Gold Foil
Florescent Screen
What he expected
Because the current model suggested:
Because, he thought the mass was evenly distributed
What he got
How he explained it
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Atom is mostly emptyAtom is mostly empty Small dense, positive piece at centerSmall dense, positive piece at center Alpha particles Alpha particles
are deflected by it if they get close are deflected by it if they get close enoughenough
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Modern ViewModern View
The atom is mostly The atom is mostly empty spaceempty space
Two regionsTwo regions Nucleus- protons Nucleus- protons
and neutronsand neutrons Electron cloud- Electron cloud-
region where you region where you have a chance of have a chance of finding an electronfinding an electron
Sub-atomic ParticlesSub-atomic Particles
Z - atomic number = number of Z - atomic number = number of protons determines type of atomprotons determines type of atom
A - mass number = number of A - mass number = number of protons + neutronsprotons + neutrons
Number of protons = number of Number of protons = number of electrons if neutralelectrons if neutral
SymbolsSymbols
XA
Z
Na23
11
Atomic mass number
Atomic number
IonsIons
Atoms or groups of atoms with a Atoms or groups of atoms with a chargecharge
Cations- positive ions - get by losing Cations- positive ions - get by losing electrons(s)electrons(s)
Anions- negative ions - get by gaining Anions- negative ions - get by gaining electron(s)electron(s)
Ionic bonding- held together by the Ionic bonding- held together by the opposite chargesopposite charges
Ionic solids are called saltsIonic solids are called salts
Ions Ions
A polyatomic ion are groups of atoms that have a chargeA polyatomic ion are groups of atoms that have a charge
Chemical symbol for ionsChemical symbol for ions
XA ± #
Atomic mass number
Periodic TablePeriodic Table
MetalsMetals ConductorsConductors Lose electronsLose electrons Malleable and ductileMalleable and ductile
NonmetalsNonmetals
BrittleBrittle Gain electronsGain electrons Covalent bondsCovalent bonds
Semi-metals or MetalloidsSemi-metals or Metalloids
Alkaline Earth Metals
Alkaline Earth Metals
Halogens
Transition metals
Noble Gases
Inner Transition Metals
+1+2 -1-2-3
NomenclatureNomenclature
Chemical BondsChemical Bonds
The forces that hold atoms togetherThe forces that hold atoms together Covalent bonding - sharing electronsCovalent bonding - sharing electrons makes moleculesmakes molecules Chemical formula- the number and type of Chemical formula- the number and type of
atoms in a molecule atoms in a molecule CC22HH66 - 2 carbon atoms, 6 hydrogen atoms, - 2 carbon atoms, 6 hydrogen atoms, Structural formula shows the connections, Structural formula shows the connections,
but not necessarily the shape.but not necessarily the shape.
There are also other model that There are also other model that attempt to show three dimensional attempt to show three dimensional shapeshape
Ball and stick Ball and stick
Space Filling Space Filling
Naming compoundsNaming compounds
Two typesTwo types IonicIonic - metal and non metal or - metal and non metal or
polyatomicspolyatomics CovalentCovalent- we will just learn the rules - we will just learn the rules
for 2 non-metalsfor 2 non-metals
Ionic compoundsIonic compounds
Write the cation first. Change the anion’s ending to -ide. Write the names of polyatomic ions. For ions with variable oxidation #’s
(Transition metals, or Tin or Lead), write the oxidation# in parentheses using Roman numerals. Remember the overall charge = 0.
Ionic CompoundsIonic Compounds
Remember you have to know what ions they form off Remember you have to know what ions they form off table, or figure it out!table, or figure it out!CaSCaSKK22SSAlPOAlPO44 KK22SOSO44FeSFeSCoICoI33
Ionic CompoundsIonic Compounds
MgOMgO MnOMnO KMnOKMnO44 NHNH44NONO33 HgHg22ClCl22 CrCr22OO33
Naming Covalent CompoundsNaming Covalent Compounds
Two words, with prefixesTwo words, with prefixes Prefixes tell you how many.Prefixes tell you how many. mono, di, tri, tetra, penta, hexa, mono, di, tri, tetra, penta, hexa,
septa or hepta, octa, nona, decasepta or hepta, octa, nona, deca First element whole name with the First element whole name with the
appropriate prefix, except monoappropriate prefix, except mono Second element, Second element, -ide -ide ending with ending with
appropriate prefixappropriate prefix
COCO22 CO CO CClCCl44 NN22OO44 XeFXeF66 NN44OO44 PP22OO1010
Naming Covalent CompoundsNaming Covalent Compounds
Writing FormulasWriting Formulas
Two sets of rules, ionic and covalentTwo sets of rules, ionic and covalent To decide which to use, decide what To decide which to use, decide what
the first element is.the first element is. If is a metal or polyatomic use ionic.If is a metal or polyatomic use ionic. If it is a non-metal use covalentIf it is a non-metal use covalent
Ionic FormulasIonic Formulas
Charges must add up to zeroCharges must add up to zero get charges from table, name of get charges from table, name of
metal ion, or memorized from the metal ion, or memorized from the listlist
use parenthesis to indicate multiple use parenthesis to indicate multiple polyatomicspolyatomics
Ionic FormulasIonic Formulas
Sodium nitrideSodium nitride sodium- Na is always +1sodium- Na is always +1 nitride - ide tells you it comes from the tablenitride - ide tells you it comes from the table nitride is Nnitride is N-3-3 doesn’t add up to zerodoesn’t add up to zero Criss-cross charges to balanceCriss-cross charges to balance
Na+1 N-3 Na3N
Ionic CompoundsIonic Compounds
Sodium sulfiteSodium sulfite calcium iodidecalcium iodide Lead (II) oxide Lead (II) oxide Lead (IV) oxideLead (IV) oxide Mercury (I) sulfideMercury (I) sulfide Barium chromateBarium chromate Aluminum hydrogen sulfateAluminum hydrogen sulfate Cerium (IV) nitriteCerium (IV) nitrite
Covalent compoundsCovalent compounds
The name tells you how to write the The name tells you how to write the formulaformula
duhduh Sulfur dioxideSulfur dioxide difluorine monoxidedifluorine monoxide nitrogen trichloridenitrogen trichloride diphosphorus pentoxidediphosphorus pentoxide
More Names and formulasMore Names and formulas
Acids and HydratesAcids and Hydrates
AcidsAcids
Substances that produce HSubstances that produce H++ ions ions when dissolved in waterwhen dissolved in water
All acids begin with HAll acids begin with H Two types of acids Two types of acids OxyacidsOxyacids non oxyacidsnon oxyacids
Naming acidsNaming acids
If the formula has oxygen in itIf the formula has oxygen in it write the name of the anion, but change write the name of the anion, but change
ate to -ic acidate to -ic acid ite to -ous acidite to -ous acid
Watch out for sulfWatch out for sulfururic and sulfic and sulfururousous HH22CrOCrO44 HMnOHMnO44 HNOHNO22
Naming acidsNaming acids
If the acid doesn’t have oxygenIf the acid doesn’t have oxygen add the prefix hydro-add the prefix hydro- change the suffix -ide to -ic acidchange the suffix -ide to -ic acid HClHCl HH22SS HCNHCN
Formulas for acidsFormulas for acids
Backwards from namesBackwards from names If it has hydro- in the name it has no If it has hydro- in the name it has no
oxygenoxygen anion ends in -ideanion ends in -ide No hydro, anion ends in -ate or -iteNo hydro, anion ends in -ate or -ite Write anion and add enough H to Write anion and add enough H to
balance the charges.balance the charges.
Formulas for acidsFormulas for acids
hydrofluoric acidhydrofluoric acid dichromic aciddichromic acid carbonic acidcarbonic acid hydrophosphoric acidhydrophosphoric acid hypofluorous acidhypofluorous acid perchloric acidperchloric acid phosphorous acid phosphorous acid
HydratesHydrates
Some salts trap water crystals when Some salts trap water crystals when they form crystalsthey form crystals
these are hydrates.these are hydrates. Both the name and the formula needs Both the name and the formula needs
to indicate how many water molecules to indicate how many water molecules are trappedare trapped
In the name we add the word hydrate In the name we add the word hydrate with a prefix that tells us how many with a prefix that tells us how many water molecules water molecules
HydratesHydrates
In the formula you put a dot and In the formula you put a dot and then write the number of molecules.then write the number of molecules.
Calcium chloride dihydrate = Calcium chloride dihydrate = CaClCaCl2222
Chromium (III) nitrate hexahydrate Chromium (III) nitrate hexahydrate = Cr(NO= Cr(NO33))33 6H 6H22O O