Atoms, Ions and MoleculesChapter 2
Daltons Atomic Theory (1808) Atoms cannot be subdivided, created, or destroyed Atoms of different elements combine in simple whole-number ratios to form chemical compounds In chemical reactions, atoms are combined, separated, or rearranged All matter is composed of extremely small particles called atoms Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties
Atomic Theory of MatterAll matter is made of tiny indivisible particles called atoms.
This proposal has been verified experimentally. Single atoms of a variety of elements have been photographed with a scanning transmission electron microscope.
Atomic Theory of Matter2. Atoms of the same element are identical and atoms of a different element have different masses and chemical properties.
However you will learn that atoms of the same element can have different masses.
Atomic Theory of MatterAtoms of different elements combine in whole number ratios to form compounds
One molecule of water always consists of two atoms of hydrogen and one atom of oxygen.
Atomic Theory of Matter4. Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed.
Modern research has altered this proposal. Atoms are not indestructible and may lose their identity when split during nuclear reactions. However Daltons proposal remains true, for chemical reactions.
Law of Multiple ProportionsAtoms of two or more elements may combine in different ratios to produce more than one compound.
A compound always contains two or more elements combined in a definite proportion by mass.Law of Constant Composition
Law of Conservation of MassThe total mass of materials present after a chemical reaction is the same as the total mass before the reaction
This is the basis for which postulate?
Parts of an AtomJ. J. Thomson - English physicist. 1897
Made a piece of equipment called a cathode ray tube.
Determined the charge to mass ratio
It is a vacuum tube - all the air has been pumped out.
Thomsons Experiment-+Vacuum tubeMetal Disks
Thomson ExperimentPassing an electric current makes a beam appear to move from the negative to the positive end-+
-By adding an electric field
Thomsons Experiment+-By adding an electric field he found that the moving pieces were negative
What Did Thomson Demonstrate?Cathode rays:
Travel in straight lines
Are negatively charged
Are deflected by electric and magnetic fields
Thomsons ModelFound the electron
Said the atom was like plum pudding
A bunch of positive stuff, with the electrons able to be removed
Robert MillikanAmerican Scientist
Goal: Determine the charge on the electron to determine its mass
Chapter 2The Discovery of Atomic StructureCathode Rays and ElectronsConsider the following experiment:Oil drops are sprayed above a positively charged plate containing a small hole. As the oil drops fall through the hole, they are given a negative charge.Gravity forces the drops downward. The applied electric field forces the drops upward.When a drop is perfectly balanced, the weight of the drop is equal to the electrostatic force of attraction between the drop and the positive plate.
Millikans ExperimentX-raysX-rays give some drops a charge.
Millikans ExperimentSome drops would hoverFrom the mass of the drop and the charge on the plates, he calculated the mass of an electron
RadioactivityDiscovered by accidentFrench scientist Henri BequerelStudying pitchblende (oxides of uranium)Discovered that it spontaneously emits high energy radiationThree types alpha- helium nucleus (+2 charge, large mass)beta- high speed electrongamma- high energy light
Rutherfords ExperimentErnest Rutherford English physicist. (1910)
Believed in the plum pudding model of the atom.
Used uranium to produce alpha particles.
Rutherfords ExperimentAimed 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 atoms thin.
Rutherfords ExperimentWhen the alpha particles hit a florescent screen, it glows.
Rutherfords ExperimentLead blockUraniumGold FoilFlorescent Screen
What he expected
Why ??The alpha particles would pass through without changing direction very much
The negative charges were spread out evenly. Alone they were not enough to stop the alpha particles
What he got
How He Explained ItAtom is mostly empty
Small dense, positive piece at center
Alpha particles are deflected by it if they get close enough
How He Explained It
Density and the AtomSince most of the particles went through, it was mostly empty.
Because the pieces turned so much, the positive pieces were heavy.
Small volume, big mass, big density
This small dense positive area is the nucleus
Discovery of the NeutronJames Chadwick bombarded beryllium-9 with alpha particles, carbon-12 atoms were formed, and neutrons were emitted.+Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 764*Walter Boethe
Modern ViewThe atom is mostly empty space
Nucleus- protons and neutrons
Electron cloud- region where you might find an electron
Structure of AtomThere are two regions:The nucleus: with protons and neutrons Almost all the mass
Electron cloud- Most of the volume of an atomThe region where the electron can be found
Size of AtomAtoms are small.
Measured in picometers, 10-12 meters
Hydrogen atom, 32 pm radius
Size of AtomNucleus tiny compared to atom
IF the atom was the size of a stadium, the nucleus would be the size of a marble.
Radius of the nucleus near 10-15m.
Density near 1014 g/cm3
Subatomic ParticlesNUCLEUSELECTRONSPROTONSNEUTRONSNegative ChargePositiveChargeNeutralChargeATOM
Subatomic particlesElectronProtonNeutronNameSymbolChargeRelative mass Actual mass (g)e-p+no-1+101/1840119.11 x 10-281.67 x 10-241.67 x 10-24
Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutronsIsotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei
SymbolsFind the number of protons
number of neutrons
number of electrons
SymbolsFind the number of protonsnumber of neutronsnumber of electronsAtomic numberMass NumberBr80 35
Symbolsif an element has an atomic number of 34 and a mass number of 78 what is the number of protonsnumber of neutronsnumber of electronsComplete symbol
Atomic MassHow heavy is an atom of oxygen?There are different kinds of oxygen atoms.More concerned with average atomic mass.Based on abundance of each element in nature.Dont use grams because the numbers would be too small
Measuring Atomic MassUnit is the Atomic Mass Unit (amu)One twelfth the mass of a carbon-12 atom. Each isotope has its own atomic mass we need the average from percent abundance.
Calculating averagesYou have five rocks, four with a mass of 50 g, and one with a mass of 60 g. What is the average mass of the rocks?
Total mass = 4 x 50 + 1 x 60 = 260 g
Average mass = 4 x 50 + 1 x 60 = 260 g 5 5
Calculating averagesAverage mass = 4 x 50 + 1 x 60 = 260 g 5 5 5Average mass = .8 x 50 + .2 x 6080% of the rocks were 50 grams20% of the rocks were 60 gramsAverage = % as decimal x mass + % as decimal x mass + % as decimal x mass +
Atomic MassCalculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass of 64.93 amu.
100908070605040302010034353637AbundanceMassMass spectrum of chlorine. Elemental chlorine (Cl2) contains only two isotopes: 34.97 amu (75.53%) and 36.97 (24.47%)AAM = (34.97 amu)(0.7553) + (36.97 amu)(0.2447)AAM = (26.412841 amu) + (9.046559 amu)AAM = 35.4594 amuCl-35Cl-37
Atomic MassMagnesium has three isotopes. 78.99% magnesium 24 with a mass of 23.9850 amu, 10.00% magnesium 25 with a mass of 24.9858 amu, and the rest magnesium 26 with a mass of 25.9826 amu. What is the atomic mass of magnesium?
If not told otherwise, the mass of the isotope is the mass number in amu
The Periodic Table
Atoms and ionsAtoms are electrically neutral.
Same number of protons and electrons.
Ions are atoms, or groups of atoms, with a charge.
Atoms and IonsDifferent numbers of protons and electrons.
Only electrons can move.
Gain or lose electrons.
AnionA negative ion.Has gained electrons.Non metals can gain electrons.Charge is written as a super script on the right.F-1Has gained one electronO-2Has gained two electrons
CationsPositive ions.Formed by losing electrons.More protons than electrons.Metals form cations.K+1Has lost one electronCa+2Has lost two electrons
Two Types of CompoundsMolecular compounds
Made of molecules.
Made by joining nonmetal atoms together into molecules.
Two Types of CompoundsIonic Compounds
Made of cations and anions.Metals and nonmetals.The electrons lost by the cation are gained by the anion.The cation and anions surround each other.Smallest piece is a FORMULA UNIT.
- Two Types of CompoundsSmallest pieceMelting PointStateTypes of elementsFormula UnitMoleculeMetal and NonmetalNonmetalssolidSolid, liquid or gasHigh >300CLow
Chemical FormulasShows the kind and number of atoms in the smallest piece of a substance.
Molecular formula- number and kinds of atoms in a molecule.
Charges on ionsFor most of the Group A elements, the Periodic Table can tell what kind of ion they will form from their location.
Elements in the same group have similar properties.
Including the charge when they are ions.
Naming ionsWe will use the systematic way.
Cation- if the charge is always the same (Group A) just write the name of the metal.
Transition metals can have more than one type of charge.Indicate the charge with roman numerals in parenthesis.
Name theseNa+1 Ca+2 Al+3 Fe+3 Fe+2 Pb+2 Li+1
Write Formulas for thesePotassium ionMagnesium ion Copper (II) ionChromium (VI) ionBarium ionMercury (II) ion
Naming AnionsAnions are always the same.
Change the element ending to ide
Write theseSulfide ion
Polyatomic ionsGroups of atoms that stay together and have a charge.You must memorize these (table 2.5).Acetate C2H3O2-1Nitrate NO3-1Nitrite NO2-1Hydroxide OH-1Permanganate MnO4-1 Cyanide CN-1
Polyatomic ionsSulfate SO4-2Sulfite SO3-2Carbonate CO3-2Chromate CrO4-2Dichromate Cr2O7-2Chlorate ClO3-Phosphate PO4-3Phosphite PO3-3Hydronium H3O + Perchlorate ClO4-Ammonium NH4+1Chlorite ClO2 -
Polyatomic IonsHypochlorite ClO-
Hydrogen carbonate ion HCO3-
Dihydrogen phosphate ion H2PO4-
Ions and Ionic Compounds
Nomenclature - HumorFerrous WheelFe = iron (Latin = ferrum)Fe2+ = lower oxidation state = ferrousFe3+ = higher oxidation state = ferricBaNa2BaNaNaWhat weapon can you make from the elements nickel, potassium and iron?A KNiFe
Naming Binary Ionic CompoundsBinary Compounds - 2 elements.Ionic - a cation and an anion.To write the names just name the two ions.Easy with Representative elements.Group ANaCl = Na+ Cl- = sodium chlorideMgBr2 = Mg+2 Br- = magnesium bromide
Naming Binary Ionic CompoundsThe problem comes with the transition metals.Need to figure out their charges.The compound must be neutral.same number of + and charges.Use the anion to determine the charge on the positive ion.
Naming Binary Ionic CompoundsWrite the name of CuONeed the charge of CuO is -2copper must be +2Copper (II) oxideName CoCl3 Cl is -1 and there are three of them = -3Co must be +3 Cobalt (III) chloride
Naming Binary Ionic CompoundsWrite the name of Cu2S.Since S is -2, the Cu2 must be +2, so each one is +1.copper (I) sulfideFe2O3 Each O is -2 Fe must be = + 3iron (III) oxide
Naming Binary Ionic CompoundsWrite the names of the following:
Ternary Ionic Compounds Will have polyatomic ionsAt least three elementsname the ionsNaNO3CaSO4CuSO3(NH4)2O
Ternary Ionic CompoundsLiCN
Writing FormulasThe charges have to add up to zero.Get charges on pieces.Cations from name of table.Anions from table or polyatomic.Balance the charges by adding subscripts.Put polyatomics in parenthesis.
Writing FormulasWrite the formula for calcium chloride.
Calcium is Ca+2
Chloride is Cl-1
Write the formulas for theseLithium sulfidetin (II) oxidetin (IV) oxideMagnesium fluorideCopper (II) sulfateIron (III) phosphidegallium nitrateIron (III) sulfide
Write the formulas for theseAmmonium chloride
Things to look forIf cations have (), the number is their charge.Transition metal
If anions end in -ide they are probably off the periodic table (Monoatomic)
If anion ends in -ate or -ite it is polyatomic
Molecular compoundsmade of just nonmetals
smallest piece is a molecule
cant be held together because of opposite charges
cant use charges to figure out how many of each atom
EasierIonic compounds use charges to determine how many of each
Have to figure out charges
Have to figure out numbers
Molecular compounds name tells you the number of atoms
Uses prefixes to tell you the number
Prefixes1 mono-2 di-3 tri-4 tetra-5 penta-6 hexa-7 hepta-8 octa-
One exception is we dont write mono- if there is only one of the first element.
Name TheseN2ONO2 Cl2O7 CBr4 CO2 BaCl2
Write formulas for thesediphosphorus pentoxidetetraiodide nonoxidesulfur hexaflouridenitrogen trioxideCarbon tetrahydridephosphorus trifluoridealuminum chloride
a little tricky so pay attention
AcidsCompounds that give off hydrogen ions when dissolved in water
Must have H in them (somewhere)
will always be some H next to an anion
The anion determines the name.
Naming acidsIf the anion attached to hydrogen ends in -ide, put the prefix hydro- and change -ide to -ic acid
HCl - hydrogen ion and chloride ion
H2S hydrogen ion and sulfide ion
Naming AcidsIf the anion has oxygen in itit ends in -ate or -itechange the suffix -ate to -ic acidHNO3 Hydrogen and nitrate ionsNitric acidchange the suffix -ite to -ous acidHNO2 Hydrogen and nitrite ionsNitrous acid
Name theseHFH3PH2SO4 H2SO3 HCNH2CrO4
Writing FormulasHydrogen will always be first
name will tell you the anion
make the charges cancel out.
Starts with hydro- no oxygen, -ide
no hydro, -ate comes from -ic, -ite comes from -ous
Write formulas for thesehydroiodic acidacetic acidcarbonic acidphosphorous acidhydrobromic acid
*h*h*The composition of different compounds formed from the same elements will always be unique*The composition of a particular substance will always be the same no matter what its origin or how it is formed.*Lord Rutherford predicted the existence of the neutron is 1920. Walter Bothe obtained evidence of the neutron in 1930. However...