Presentation on theme: "Chapter 5 “Atomic Structure”"— Presentation transcript:
1Chapter 5 “Atomic Structure” ChemistryOlympic High SchoolMr. DanielCredits: Stephen L. CottonCharles Page High School
2Section 5.1 Defining the Atom OBJECTIVES:Describe the history of the development of ideas about atoms.Explain Dalton’s atomic theory.Describe the size of the atom.
3Section 5.1 Defining the Atom The Greek philosopher Democritus (460 B.C. – 370 B.C.) was among the first to suggest the existence of atoms (from the Greek word “atomos” – meaning “unable to be cut”)
4Antoine Laurent Lavoisier ( ) The Father of Modern Chemistry: discovered oxygen & hydrogen, developed modern thermodynamics, invented the first periodic table
5Dalton’s Atomic Theory (experiment based) All elements are composed of tiny indivisible particles called atomsAtoms of the same element are identical. Atoms of any one element are different from those of any other element.John Dalton(1766 – 1844)Atoms of different elements combine in simple whole- number ratios to form chemical compoundsIn chemical reactions, atoms are combined, separated, or rearranged – but never changed into atoms of another element.
6Section 5.2 Structure of the Nuclear Atom OBJECTIVES:Identify three types of subatomic particles and their properties.Describe the structure of atoms, according to the Rutherford Model.
7Section 5.2 Structure of the Nuclear Atom One change to Dalton’s atomic theory is that atoms are divisible into subatomic particles:Electrons, protons, and neutrons are examples of these fundamental particlesThere are many other types of particles, but we will study these three
8The electron’s charge-to-mass ratio = 1.76 108 C/g In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle: the electronJJ ThomsonlThe electron’s charge-to-mass ratio = 1.76 108 C/g
9A Standard Television Tube (First common in the 1950’s) Cathode Ray TubesA Standard Television Tube (First common in the 1950’s)A CRT from a Radar Scope (WW II)Standard Computer Monitor (often called a “CRT”)Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.
10Mass of the ElectronsimulationRobert MillikanMass of the electron is9.11 x gThe oil drop apparatus1916 – Robert Millikan determined the mass of the electron: 1/1840 the mass of a hydrogen atom; has one unit of negative charge
11Conclusions from the Study of the Electron: Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons.Atoms are neutral, so there must also be positive particles in the atom to balance the negative charge of the electronsElectrons have very little mass, therefore atoms must contain other particles that account for most of the mass
12Thomson’s Atomic Model J. J. ThomsonThomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.
13Other Particle Discoveries: Eugen Goldstein first observed evidence of what is now called the “proton” in particles with a positive charge, and a mass of 1840 times that of an electron. It’s existance was later confirmed by Ernest Rutherford in 1919.1932 – James Chadwick confirmed the existence of the “neutron” – a particle with no charge, but a mass nearly equal to a proton
14The problem:In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?Target #1The Answer:
16Ernest Rutherford’s Gold Foil Experiment - 1911 Alpha particles are helium nuclei - The alpha particles were fired at a thin sheet of gold foilParticle that hit on the detecting screen (film) are recorded
17Rutherford’s Findings Most of the particles passed right throughA few particles were deflectedVERY FEW were greatly deflected“Like howitzer shells bouncing off of tissue paper!”Conclusions:The nucleus is smallThe nucleus is denseThe nucleus is positively charged
18The Rutherford Atomic Model Based on his experimental evidence, Rutherford’s Nuclear Model was developed and stated:The atom is mostly empty spaceThe electrons are distributed around the nucleus, and occupy most of the volumeBecause of the exceptionally high mass of the nucleus, it must contain particles in addition to protons (neutrons were discovered later)All the positive charge, and almost all the mass is concentrated in a small area in the center. He called this a “nucleus”Ernest Rutherford video
19Subatomic Particles Particle Charge Mass (g) Location Crash Course Chemistry - History of Chemical ConceptsParticleChargeMass (g)LocationElectron x Electron(e-) cloudProton x Nucleus(p+) (1 atomic mass unit)Neutron x Nucleus(no) (1 atomic mass unit)
20Sizing up the AtomElements can be subdivided into smaller and smaller pieces until there are only single atoms; The smallest particles of an element that still have the properties of that element.100,000,000 copper atoms in a single file, would be approximately 1 cm longDespite their incredibly small size, individual atoms have recently become observable with scanning tunneling microscopesThe Beginning: Xe on NiAtomic Kanji “original child”Forming a Image: Fe atoms on a Cu surfaceImage: Fe atoms on a Cu surfaceImage: Fe atoms on a Cu surfaceAn Artistic View of NiCarbon Monoxide Man
21Section 5.3 Distinguishing Among Atoms OBJECTIVES:Explain what makes isotopes different from each other.Calculate the number of protons, neutrons and electrons in an atom using atomic number and massCalculate the average atomic mass and atomic number.
22Atomic Number Element # of protons # of electrons Atomic # (Z) Carbon Atoms are composed of protons, neutrons, and electronsHow then are atoms of one element different from another element?Elements are different because they contain different numbers of PROTONSAtomic number (Z) : the number of protons in the nucleus of each atom of that element.An atom is always neutral, therefore:# protons in an atom = # electronsElement# of protons# of electronsAtomic # (Z)Carbon6Phosphorus15Iodine53Gold79
23Mass Number Nuclide p+ n0 e- Mass # Mass number is the number of protons and neutrons in the nucleus of an atom:Mass # = p+ + n0Nuclidep+n0e-Mass #Oxygen -10-3342- 3115188818Arsenic753375Phosphorus161531
24X Complete Symbols Mass U Complete Symbols contain the symbol of the element, the mass number and the atomic number.Examples:CUMassnumberSuperscript →12X6146235AtomicnumberSubscript →92
25Symbols continued…We can also put the mass number after the name of the element:carbon-12carbon-14uranium-235
26Br 80 35 Symbols Find each of these: number of protons number of neutronsnumber of electronsAtomic numberMass Number35 b) 45 c) 35 d) 35 e) 80
27SymbolsIf an element has an atomic number of 34 and a mass number of 78, what is the:number of protonsnumber of neutronsnumber of electronscomplete symbol34 b) 44 c) 34 d) Se7834
28Symbols If an element has 91 protons and 140 neutrons what is the Atomic numberMass numbernumber of electronscomplete symbol91 b) 231 c) 91 d) Pa23191
29Symbols If an element has 78 electrons and 117 neutrons what is the Atomic numberMass numbernumber of protonscomplete symbol78 b) 195 c) 78 d) Pt19578
30IsotopesDalton was wrong about all elements of the same type being identical:Atoms of the same element can have different numbers of neutrons.Thus, they have different mass numbers.These are called isotopes.
31Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons. ProtonsElectronsNeutronsNucleusHydrogen–1(protium)1Hydrogen-2(deuterium)Hydrogen-3(tritium)2
32IsotopesElements occur in nature as mixtures of isotopes.
33Atomic Mass How heavy is an atom of oxygen? It depends, because there are different kinds of oxygen atoms.We generally refer to the average atomic mass.Average atomic mass is based on the abundance (percentage) of each isotope of an element as it is found in nature.It is the number (red) that we find on the periodic table
34Measuring Atomic MassInstead of grams, the mass unit we use for atoms is the Atomic Mass Unit (amu or µ)It is defined as one-twelfth the mass of a carbon-12 atom.Carbon-12 is chosen because of its isotope purity.Each isotope has its own atomic mass, thus we determine the average mass from the percent abundance of each isotope.
35Composition of the nucleus Atomic MassesAtomic mass is the average of all the naturally occurring isotopes of that element.IsotopeSymbolComposition of the nucleus% in natureCarbon-1212C6 protons6 neutrons98.89%Carbon-1313C7 neutrons1.11%Carbon-1414C8 neutrons<0.01%Carbon = µ
36To calculate the average atomic mass: Multiply the mass number of each isotope by its abundance (expressed as a decimal), then add the results.The mass of the isotope is expressed in atomic mass units (amu or µ)IsotopeSymbol% in natureCarbon-1212C98.89%Carbon C 1.11%Carbon C <0.01%12.01 µ(12.00 µ) (.9889) +(13.00 µ) (.0111) =
37Atomic Mass Calculation Element X has two natural isotopes. The isotope with a mass of amu has a relative abundance of 19.91%. The isotope with a mass of amu has a relative abundance of 80.09%. Calculate the atomic mass of this element.( µ) (.1991) + ( µ) (.8009) =10.81 µBoron
38Section 5.4 Organizing the Elements OBJECTIVES:Explain how elements are organized in a periodic table.Compare early and modern periodic tables.Identify three broad classes of elements.Distinguish different areas of the periodic table.
39Section 5.4 Organizing the Elements A few elements, such as gold and copper, have been known for thousands of years.Yet, only about 13 (of 90) had been identified by the year 1700.As more were discovered, chemists realized they needed a way to organize the elements.
40Section 5.4 Organizing the Elements Chemists used the properties of elements to sort them into groups.In 1829 J. W. Dobereiner arranged elements into triads – groups of three elements with similar properties ( ) ÷ 2 = 88Ca 40 Sr 88 Ba 137Li Na 23 K 39Cl Br I
41John Newlands ( )Law of Octaves: noted that after interval of eight elements, similar physical/chemical properties reappeared. Newlands was the first to formulate the concept of periodicity (repeating patterns) in the properties of the chemical elements.
42Mendeleev’s Periodic Table Lothar MeyerMendeleev’s Periodic TableBy the mid-1800s, about 70 elements were known to existDmitri Mendeleev – A Russian chemist arranged the elements in order of increasing atomic massIt was the beginning of the modern “Periodic Table”
43Co and Ni; Ar and K; Te and I His Completed Work…His Original Table…Co and Ni; Ar and K; Te and IMendeleev left blanks for elements he predicted that existed such as GermaniumBut, there were problems: some elements did not fit with their groupsWhen discovered, the elements generally matched his predictions
44A better arrangement…In 1913, Henry Moseley – British physicist, arranged elements according to increasing atomic numberHis basic arrangement is still used todayThe symbol, atomic number & mass are the basic items included in the periodic table
45Squares in the Periodic Table The periodic table displays the symbols and names of the elements, along with atomic number and average atomic massBlack symbol = solidRed symbol = Blue symbol = liquid25º C
47There are other possible arrangements. How about a: Spiral Periodic Table
48The Periodic Table:Your “best friend” is an arrangement of elements in which they are separated into groups based on a set of repeating properties.The periodic table allows you to easily compare the properties of one element to another
49The Periodic Law Vertical column = group (or family) Similar physical & chemical propertiesIdentified by number & letterHorizontal rows = periodsRepeated properties in each rowThere are 7 periodsWhen elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.
50Areas of the periodic table Three classes of elements are:1) Metals 2) Nonmetals 3) Metalloids
51MetalsMetals: electrical conductors, have luster, are ductile and malleable (in pink below)
52Nonmetals: generally brittle and dull, are poor conductors of heat and electricity (in blue below) Some nonmetals…are gases (O, N, Cl);are brittle solids (S, C);one is dark red liquid (Br)
53Notice the heavy, stair-step line… Metalloids: border the lineTheir properties are intermediate between metals and nonmetals (in green below)
54Elements in the 1A-7A groups are called the Representative Elements Have very predictable properties and patterns of behavior1A8A2A3A4A5A6A7A
55Groups of elements Group IA – Alkali Metals Alkali Metals Are the most reactive metalsForm a “base” when reacting with waterAlkali Metals
56Groups of Elements Alkaline Earth Metals Group 2A – Alkaline Earth MetalsAre the second most reactive metalsAlso form bases with water, but do not dissolve well; hence “earth metals”Alkaline Earth Metals
57Groups of elements The Halogen Group Group 7A – Halogens The most reactive non-metal groupMeans “salt-forming”The Halogen Group
58Groups of elements Noble Gases Group 8A- Noble Gases Previously called “inert gases” because they rarely take part in a reactionNoble gases have a completely full electron arrangementNoble Gases
59The “B” groups are called the Transition Elements LaAcLanthanide SeriesActinide SeriesThe “Inner Transition Metals” actually belong hereCrash Course Chemistry - The Periodic Table