3Greek PhilosophersEarly philosophers debated the fundamental “stuff” of which the universe was madeDemocritus’ idea of the world was based on “atomos” meaning indivisible or uncuttableLater Plato and Aristotle formulated that there can be no uncuttable “things” and they successfully propagated their theory and therefor became the dominant theory for centuries
4John Dalton The atom reemerged in the 17th century The ground work was laid by John Dalton when he noticed that elements that reacted with other elements to form new compoundsDalton’s atomic theory was based on 4 postulates
5Dalton’s Atomic Theory Explains several laws that were known during Dalton’s time, including the law of constant composition.In a given compound, the relative numbers and kinds of atoms are constantThe Law of Conservation of MassThe total mass of materials present after a chemical reaction is the same as the total mass present before the reactionThe Law of Multiple ProportionsIf two elements A and B combine to form more than one compound, the masses of B that can combine with given mass of A are in the ratio of small whole numbers
8Give it some thoughtCompound A contains g of oxygen per gram of carbon, whereas compound B contains g of oxygen per gram of carbon.What chemical law does this data illustrate?Law of Multiple ProportionsIf compound A has an equal number of oxygen and carbon atoms, what can we conclude about the composition of compound B?There are twice as many oxygen atoms in compound B than there is in compound A
10Subatomic ParticlesDalton based his theory on observations made in the laboratoryHe and those who followed had no direct evidence of the atomAs time progressed, scientists began to probe the nature of matter and started to discover subatomic particlesWe will see that the atom is composed in part by electrically charged particlesKeep in mind as we continue that same charges repel one another, whereas particles with unlike charges attract one another
11Cathode Rays and Electrons (e-) During the 1800’s scientists experimented (including Thomson) with evacuated glass tubes with electrodes inserted at both endsOnce a charge was applied a radiation between the electrodes was producedCathode rays emanated from the negative end and traveled to the positive endThe rays were unseen but caused certain materials to fluoresceThe rays were tested with magnets and electrically charged rods and it was found that the cathode rays were negatively chargedThe identity of the new particle was the same regardless of the gas usedThis new “thing” was called the electronThomson tested the beam and found that there was 1.76 x 108 coulombs per gram
14Give it some thoughtThomson observed that the cathode rays produced in the cathode–ray tube behaved identically, regardless of the particular metal used as cathode. What is significance of this observation?All atoms have the same subatomic particles called electrons!
15Millikan Oil Drop Experiment Once the charge-to-mass ratio of the electron was known, Milikan was then able to experimentally figure out the mass of the electronUsing an experiment similar to the one pictured to the right he calculated the mass of the electron to be 9.10 x g by solving the charge of a single electronThis showed that the electron has a mass of about 2000 times less than hydrogen!
16RadioactivityIn 1896, Henri Becquerel discovered that uranium emitted radiation.Spontaneous emission is known as radioactivityHe concluded that the source or the radiation was the uranium atomsStudies done by Ernest Rutherford showed that there were 3 types of radiationAlpha (α)Beta (β)Gamma (γ)Alpha and beta radiation was shown to be bent by an electric field (but in different directions) while gamma radiation was unaffected by it
17α and β Rays Both considered fast moving particles Beta rays were shown to be the radioactive equivalent of cathode raysAttracted to positively charged plates!Charge of -1The alpha particles were shown to have a positive chargeCharge of +2Has a mass 7400 times that of an electronGamma radiation is high-energy radiation similar to X-rays and does not consist of particles and carries no charge
19Thomson ModelThomson in the early 1900’s reasoned that since the electrons are such a small portion of the mass of the atom that it must also only make up a small portion of the atomThomson proposed that that the electrons were embedded in the atom like raisons in puddingThe “pudding” having a positive charge
20Rutherford Atomic Model Rutherford was studying the angles at which alpha particles were being deflectedHe discovered that most particles passed straight through the gold foil while only a small amount of the particles were deflected or even bounced backRutherford explained the result by postulating the nuclear model of the atom, which most of the mass of each gold atom resided in the nucleusHe postulated that the majority of the space in an atom was empty and that the charge of the nucleus was positive
21Protons and NeutronsSubsequent experiments led to the discovery of positive particles (protons) and neutral particles (neutrons) in the nucleus.Protons were discovered in 1919 by Rutherford and neutrons in 1932 by British scientist James Chadwick (1891–1972). Thus, the atom is composed of electrons, protons, and neutrons.
22Give it Some ThoughtWhat happens to most of the alpha particles that strike the gold foil in Rutherford’s experiment?They passed straight throughWhy do they behave that way?The atom is mostly empty space
24The Modern View of Atomic Structure The charge of an electron is * C.The charge of a proton is opposite in sign but equal in magnitude to that of an electron: * C.The quantity * C is called the electronic charge.For convenience, the charges of atomic and subatomic particles are usually expressed as multiples of this charge rather than in coulombs.The charge of an electron is 1- and that of a proton is 1+.Neutrons are electrically neutralEvery atom has an equal number of electrons and protons, so atoms have no net electrical charge.
25Atomic DiameterProtons and neutrons reside in the center of the atom and take up only a small volume of the atomMost atoms have diameters between 1 * m 1100 pm2 and 5 * m 1500 pm2. A convenient non–SI unit of length used for atomic dimensions is the angstrom 1A° 2, where 1 A° = 1 * m. Thus, atoms have diameters of approximately A° . The diameter of a chlorine atom, for example, is 200 pm, or 2.0 A° .
26Give it Some ThoughtIf an atom has 15 protons, how many electrons does it have?PhosphorousWhere do the protons reside in an atom?The nucleus
30Atomic Numbers, Mass Numbers, and Isotopes The atoms of each element have a characteristic number of protons. The number of protons in an atom of any particular element is called that element’s atomic number.Because an atom has no net electrical charge, the number of electrons it contains must equal the number of protons.The atomic number is indicated by the subscript; the superscript, called, the mass number is the number of protons and neutrons
31IsotopesIsotopes differ by the number of neutrons but contain the same number of protons
35Atomics Mass ScaleScientists in the 19th century were aware that atoms of different elements have different massesThey knew that in water that there was 88.9 g of oxygen for every 11.1 grams of hydrogen in 100 grams of waterToday we can determine the masses of individual atoms with a high degree of accuracy.The atomic mass unit is a convenient way when dealing with very small massesi.e 1 mole of carbon twelve weights 12 amu
36Atomic WeightAtomic weight is the natural mixture of isotopes found in natureTo calculate the atomic weight of an element is to use the following equation:Atomic Weight = Σ[(isotope mass) x (fractional isotope abundance)]Σ sigma means over all masses
37Give it Some ThoughtA particular atom of chromium has a mass of amu, whereas the atomic weight of chromium is given as amu. Explain the difference in the two masses.
40Some Pictures From Mr. Hunter’s Graduate Research
41Actual Data Gathered by Mr. Hunter Why are there bands over a certain mass range and not just a line?The mass spectrometer is an energy filter that allows only stable trajectories of ions through.Therefore, all ions of the same mass have a range of energies (different velocity) coming fromthe ion source.
42Book Work in Class Pages 74-75 Answer only red questions for section
44The Periodic TableAs the list of elements began to grow throughout history, certain elements were noticed to have similar traits as other elements.For example, Na and K had similar properties while He and Ne also had similar properties to one another.These similarities became known as periodic trends or families
50Molecules and Molecular Compounds All of the pictured molecules arein their chemical formulas exceptfor oneOxygen and hydrogen exist as diatomic elements,i.e moleculeMolecules that contain more than one type of atomare called molecular compounds
51Molecular and Empirical Formulas Chemical formulas that indicated the exact number of atoms in a molecule are called molecular formulasChemical formulas that indicate the relative number of atoms in a molecule are called empirical formulas
53Picturing MoleculesStructural formulas shows which atoms are attached to whichAtoms can be represented by their symbols and bonds by linesThis type of modeling does not show the actual geometry of the moleculeThe Ball-and Stick model has the advantage of showing the actual geometry of the atoms in relation to one anotherThe space filling model shows the relative sizes of atoms and their geometries
57Ions and Ionic Compounds An ion is a charged particleA cation is a positive particle (one or more less electrons)An anion is a negative particle (one or more extra electrons)Ions form because certain elements have a weak attraction to the outer electrons (valence electrons)Other elements have a strong attraction for their electrons and surrounding elements electronsThe stronger pull can take the weaker element’s electronThis transfer of electrons causes ions to formIn addition to simple ions there are polyatomic ions such as ammonium and sulfateThese ions are made of at least 2 elements
59Predicting Ionic Charges Elements like to have a stable number of electrons.The most stable elements on the periodic table are the noble gases because they have a full octet of electronsElements gain or lose electrons to get to this stable stateNonmetals tend to gain electronsMetals tend to lose electronsHalf Filled shells are more stable that partially filled shellsMeaning, electrons can move from one shell to another to stabilize the ionThis also means that s-orbital electrons can be taken instead of f- or d-shell electrons
60Practice ProblemPredict the charge states of:FeSnScTiV
67Criss-Cross MethodSince there are not discrete ionic “molecules” we are only able to write empirical formulas for these compoundsThe criss-cross method take the charges of each ion and puts it down at the subscript of the opposite ion
70Naming Inorganic Compounds Chemical Nomenclature comes from the latin word nomen (name) and calare (to call)The rules of chemical nomenclature are based on the division of substances into categoriesOrganic compounds contain carbon and hydrogen often with oxygen, nitrogen, and other elementsAll other compounds are inorganic compounds
71Names and Formulas of Ionic Compounds Most metals that form cations can form different oxidation states. These are usually transition metals
83Names and Formulas of Binary Molecular Compounds The name of the element farther to the left in the periodic table (closest to the metals) is usually written first. An exception occurs when the compound contains oxygen and chlorine, bromine, or iodine (any halogen except fluorine), in which case oxygen is written last.If both elements are in the same group, the one closer to the bottom of the table isnamed first.The name of the second element is given an -ide ending.Greek prefixes indicate the number of atoms of each element.(Exception: The prefix mono- is never used with the first element.) When the prefix ends in a or o and the name of the second element begins with a vowel, the a or o of the prefix is often dropped.
88Organic ChemistryThe study of compounds containing carbon is called organic chemistryOrganic chemistry is a very important branch of chemistry encompassing a large portion or what chemists doBeing able to name these compounds is very important for the standardization of chemistry experimentsHydrocarbons are composed of only carbon and hydrogenAlkanes are the simplest of hydrocarbonsAlkanes always end in -ane
89Some Derivatives of Alkanes Functional groups can be added to organic molecules to change their chemical propertiesAlcohols are made by adding an –OH group in place of a hydrogenAn alcohol has the ending –olNumbers are used to determine what carbon the functional group is attachedAlways use numbers that make it the smallest possible number or smallest possible addend
90IsomersIsomers are compounds that have the same molecular formulas but a different chemical arrangementThe most common type of isomer are structural isomers
91Other Functional Groups There are hundreds of different functional groups in organic chemistryCommon functional groups are:HalogensHydroxyl (-OH)Carboxylic acid (-COOH)Oxygen insertionsCarbonyl groups (-CO)Alkane groups