Presentation on theme: "Unit 4: The Nature of Matter"— Presentation transcript:
1Unit 4: The Nature of Matter Table of Contents17Unit 4: The Nature of MatterChapter 17: Properties of Atoms and the Periodic Table17.1: Structure of the Atom17.2: Masses of Atoms17.3: The Periodic Table
2Structure of the Atom17.1Scientific ShorthandScientists have developed their own shorthand for dealing with long, complicated names.Chemical symbols consist of one capital letter or a capital letter plus one or two smaller letters.
3Structure of the Atom17.1Scientific ShorthandFor some elements, the symbol is the first letter of the element's name.For other elements, the symbol is the first letter of the name plus another letter from its name.Because scientists worldwide use this system, everyone understands what the symbols mean.
4Structure of the Atom17.1Atomic ComponentsAn element is matter that is composed of one type of atom, which is the smallest piece of matter that still retains the property of the element.Atoms are composed of particles called protons, neutrons, and electrons.Click image to view movie
5Structure of the Atom17.1Atomic ComponentsProtons and neutrons are found in a small positively charged center of the atom called the nucleus that is surrounded by a cloud containing electrons.Protons are particles with an electrical charge of 1+.
6Structure of the Atom17.1Atomic ComponentsElectrons are particles with an electrical charge of 1–.Neutrons are neutral particles that do not have an electrical charge.
7Quarks—Even Smaller Particles Structure of the Atom17.1Quarks—Even Smaller ParticlesProtons and neutrons are made up of smaller particles called quarks.So far, scientists have confirmed the existence of six uniquely different quarks.
8Quarks—Even Smaller Particles Structure of the Atom17.1Quarks—Even Smaller ParticlesScientists theorize that an arrangement of three quarks held together with the strong nuclear force produces a proton.Another arrangement of three quarks produces a neutron
9Structure of the Atom17.1Finding QuarksTo study quarks, scientists accelerate charge particles to tremendous speeds and then force them to collide with—or smash into—protons. This collision causes the proton to break apart.The particles that result from the collision can be detected by various collection devises.
10Models—Tools for Scientists Structure of the Atom17.1Models—Tools for ScientistsScientists and engineers use models to represent things that are difficult to visualize—or picture in your mind.Scaled-down models allow you to see either something too large to see all at once, or something that has not been built yet.Scaled-up models are often used to visualize things that are too small to see.
12Studying Atoms Different Models of the atom Greek Model Dalton’s Atomic TheoryThomson’s ModelRutherford’s Atomic TheoryBohr’s Model of the AtomElectron Cloud Model
13Models—Tools for Scientists Structure of the Atom17.1Models—Tools for ScientistsTo study the atom, scientists have developed scaled-up models that they can use to visualize how the atom is constructed.For the model to be useful, it must support all of the information that is known about matter and the behavior of atoms.
14Aristotle These elements were a combination of 4 qualities Aristotle thought that all substances were built up from only 4 elementsEarthAirFireWaterThese elements were acombination of 4 qualitieshot, cold, dry, and wet
17Aristotle For centuries people believed this model. Aristotle did not think there was a limit to the number of times matter could be divided.For centuries people believed this model.
18Defining the AtomThe Greek philosopher Democritus (460 B.C. – 370 B.C.) was among the first to suggest the existence of atoms (from the Greek word “atomos”) ATOMHe believed that atoms were indivisible and indestructibleHis ideas did agree with later scientific theory, but did not explain chemical behavior, and was not based on the scientific method– but just philosophy
19Greek Model Democritus Greek philosopher Idea of ‘democracy’ “To understand the very large,we must understand the very small.”DemocritusGreek philosopherIdea of ‘democracy’Idea of ‘atomos’Atomos = ‘indivisible’‘Atom’ is derivedNo experiments to support ideaContinuous vs. discontinuous theory of matterDemocritus’s model of atomNo protons, electrons, or neutronsSolid and INDESTRUCTABLE
20Who Was Right? Greek society was slave based Beneath famous to work with handsdid not experimentGreeks settled disagreements by argumentAristotle was more famousHe won!His ideas carried through middle ages.Alchemists change lead to goldCalifornia WEB
22John Dalton John Dalton (1766-1844) was known as the “Father of the modern atom.”He was the first to actually test, previously the Greeks would just theorize. In his work he developed Dalton's Atomic Theory.
23The Changing Atomic Model Structure of the Atom17.1The Changing Atomic ModelIn the 1800s, John Dalton, an English scientist, was able to offer proof that atoms exist.Because Dalton’s atomic theory was proven through many experiments His THEORY became widely accepted.
24Dalton’s Atomic Theory (experiment based) All elements are composed of tiny indivisible particles called atomsAtoms of the same element are identical.Atoms Can’t be Created nor Destroyed!John Dalton(1766 – 1844)4) Atoms of different elements combine in simple whole-number ratios to form chemical compounds5) In a particular compound, atoms of different elements always combine in the same way6) All atoms of the same element have the same mass, atoms of diff. elements have diff. masses
25Dalton’s Model The Elements are pictured as solid spheres: Each type of atom is represented by a tiny, solid sphere with a different mass.
28JJ. Thomson J.J. used the idea behind charges: -- Like charges repel -- Unlike charges attractWith this idea in mind, J.J. used electric current to study the atom. Remember my ex: with the Magnets
29- + Crooke’s Tube voltage source Sir William Crookes ( ) was the British scientist who invented the cathode ray tube. His work paved the way to the discovery of the electron.voltagesourceWilliam Crookes-+magnetvacuum tubemetal disksCrooke’s Tube
30Discovery of the Electron Looking at what JJ saw, what do you think he determined was the charge on the particles in the beam?
31- Thomson’s Experiment + voltage source + - OFF++-By adding an electric field…he found that the moving pieces were negative.
32In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle: the electron The Electron was named by G. Johnstone Stoney !** Thomsons experiments were the 1st proof that atoms are made of smaller particles.
33Mass of the ElectronMass of the electron is9.11 x gThe oil drop apparatus1916 – Robert Millikan determines the mass of the electron: 1/1840 the mass of a hydrogen atom; has one unit of negative charge
34Conclusions 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 be positive particles in the atom to balance the negative charge of the electronsElectrons have so little mass that atoms must contain other particles that account for most of the mass
35Magnetic PropertiesShow ex: of Plastic rubbed in hair and held to Water Source!
36Some Modern Cathode Ray Tubes Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.
37J.J. ThomsonJ.J. reasoned that if the atom had negative little particles inside it, but was considered to be NEUTRAL, then there must also be some positive particles too.
38Thomson’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.
39Conclusions from the Study of the Electron: Eugen Goldstein in 1886 observed what is now called the “proton” - particles with a positive charge, and a relative mass of 1 (or 1840 times that of an electron)1932 – James Chadwick confirmed the existence of the “neutron” – a particle with no charge, but a mass nearly equal to a proton
41Ernest Rutherford (1871-1937) Learned physics in J.J. Thomson’ lab. Noticed that ‘alpha’ particles were sometime deflected by something in the air.Gold-foil experiment
42Ernest 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
43Rutherford ‘Scattering’ In 1909 Rutherford undertook a series of experimentsHe fired a (alpha) particles at a very thin sample of gold foilAccording to the Thomson model the a particles should onlybe slightly deflectedRutherford discovered that they were deflected through large angles and could even be reflected straight back to the sourceparticlesourceLead collimatorGold foilaq
44Rutherford’s 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 #2Target #1
46Rutherford’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
48The Rutherford Atomic Model Based on his experimental evidence:The atom is mostly empty spaceAll the positive charge, and almost all the mass is concentrated in a small area in the center. He called this a “nucleus”
49The Rutherford Atomic Model The nucleus is composed of protons and neutronsThe electrons distributed around the nucleus, and occupy most of the volumeHis model was called a “nuclear model”
51Niels BohrIn the Bohr Model (1913) the neutrons and protons occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun.They are not confined to a planar orbit like the planets are.
52Bohr ModelPlanetarymodelAfter Rutherford’s discovery, Bohr proposed that electrons travel in definite orbits at constant speeds around the nucleus like planets around the sun.
53Staircase IdeaTo understand energy levels, picture them as steps in a staircase.Just as you can’t stand on 2 steps at one time, Electrons can’t occupy more than 1 energy level at a time.Bottom step = Lowest Energy LevelTop Step = Highest Energy LevelCont…
54Staircase ModelAn electron in an ATOM can move from one energy level to another if enough energy is provided.The size of the jump ( 1 level or 2) determines the amt. of energy gained or lost.
55Humor Two atoms are walking down the street. One atom says to the other, “Hey! I think I lost an electron!”The other says, “Are you sure??”“Yes, I’m positive!”A neutron walks into a restaurant and orders a coupleof drinks. As she is about to leave, she asks the waiterhow much she owes. The waiter replies, “For you,No Charge!!!”
56The Electron Cloud Model Structure of the Atom17.1The Electron Cloud ModelBy 1926, scientists had developed the electron cloud model of the atom that is in use today.An electron cloud is the area around the nucleus of an atom where its electrons are most likely found.
57The Electron Cloud Model Structure of the Atom17.1The Electron Cloud ModelThe electron cloud is 100,000 times larger than the diameter of the nucleus.In contrast, each electron in the cloud is much smaller than a single proton.Because an electron's mass is small and the electron is moving so quickly around the nucleus, it is impossible to describe its exact location in an atom.EX: Propeller of an Airplane’s wings !
58Section Check17.1Question 1Which is the smallest piece of matter that still retains the property of the element?A. atomB. quarkC. neutronD. proton
59Section Check17.1AnswerThe answer is A. An atom is the smallest piece of matter that still retains the property of the element.
60Question 2 17.1 What particles are found in the nucleus of an atom? Section Check17.1Question 2What particles are found in the nucleus of an atom?A. protons and electronsB. protons and neutronsC. neutrons and electronsD. quarks and electrons
61Section Check17.1AnswerThe answer is B. Electrons are located in an electron cloud surrounding the nucleus of the atom.
62Section Check17.1Question 3What is the name of the small particles that make up protons and neutrons?AnswerProtons and neutrons are made of smaller particles called quarks.
63Question 4The Greek philosopher Democritus coined what word for a tiny piece of matter that cannot be divided?a. element c. electronb. atom d. moleculeAnswer: Atom
64Question 5Which of the following is NOT part of John Dalton’s atomic theory?a. All elements are composed of atoms.b. All atoms of the same element have the same mass.c. Atoms contain subatomic particles.d. A compound contains atoms of more than one element.Answer: c
65Question 6Which of the following most accurately represents John Dalton’s model of the atom?a. a tiny, solid sphere with an unpredictable mass for a given elementb. a hollow sphere with a dense nucleusc. a tiny, solid sphere with predictable mass for a given elementd. a sphere that is hollow throughout6) Answer: c
66Question 7 JJ Thomson’s experiments provided evidence that an atom a. is the smallest particle of matter.b. contains negatively charged particles.c. has a negative charge.d. has a positive charge.Answer: b
67Question 8Rutherford’s gold foil experiment provided evidence for which of the following statements?a. Negative and positive charges are spread evenly throughout an atom.b. Alpha particles have a positive charge.c. Gold is not as dense as previously thought.d. There is a dense, positively charged mass in the center of an atom.Answer: d
68Question 9Who provided evidence for the existence of a nucleus in an atom?a. John Dalton c. Democritusb. J.J. Thomson d. Ernest RutherfordAnswer: d.
69Question 10In an atomic model that includes a nucleus, positive charge isa. concentrated in the center of an atomb. spread evenly throughout an atom.c. concentrated at multiple sites in an atom.d. located in the space outside the nucleus.Answer: a
71Masses of Atoms17.2Atomic MassThe nucleus contains most of the mass of the atom because protons and neutrons are far more massive than electrons.The mass of a proton is about the same as that of a neutron—approximately
72Masses of Atoms17.2Atomic MassThe mass of each is approximately 1,836 times greater than the mass of the electron.
73Masses of Atoms17.2Atomic MassThe unit of measurement used for atomic particles is the ______________________.atomic mass unit (amu)The mass of a proton or a neutron is almost equal to 1 amu.The atomic mass unit is defined as one-twelfth the mass of a carbon atom containing six protons and six neutrons.
74Protons Identify the Element Masses of Atoms17.2Protons Identify the ElementThe number of protons tells you what type of atom you have and vice versa. For example, every carbon atom has six protons. Also, all atoms with six protons are carbon atoms.The number of protons in an atom is equal to a number called the atomic number.
75Masses of Atoms17.2Mass NumberThe mass number of an atom is the sum of the number of protons and the number of neutrons in the nucleus of an atom.
76Masses of Atoms17.2Mass NumberIf you know the mass number and the atomic number of an atom, you can calculate the number of neutrons.number of neutrons = mass number – atomic number
77Not all the atoms of an element have the same number of neutrons. Masses of Atoms17.2IsotopesNot all the atoms of an element have the same number of neutrons.Atoms of the same element that have different numbers of neutrons are called isotopes.Remember – Protons Never Change
78Masses of Atoms17.2Identifying IsotopesModels of two isotopes of boron are shown. Because the numbers of neutrons in the isotopes are different, the mass numbers are also different.You use the name of the element followed by the mass number of the isotope to identify each isotope: boron-10 and boron-11.
80Masses of Atoms17.2Identifying IsotopesThe average atomic mass of an element is the weighted-average mass of the mixture of its isotopes.For example, four out of five atoms of boron are boron-11, and one out of five is boron-10.To find the weighted-average or the average atomic mass of boron, you would solve the following equation:
81Plug the following in on a calculator Order:4 / 5 X 11 = ?1 / 5 X 10 = ?Add the 2 numbers = ?
82Section Check17.2Question 1How is the atomic number of an element determined?AnswerThe atomic number of an element is equal to the number of protons in an atom of that element.
83Section Check17.2Question 2The element helium has a mass number of 4 and atomic number of 2. How many neutrons are in the nucleus of a helium atom?
84Section Check17.2AnswerRecall that the atomic number is equal to the number of protons in the nucleus. Since the mass number is 4 and the atomic number is 2, there must be 2 neutrons in the nucleus of a helium atom.
85Section Check17.2Question 3How much of the mass of an atom is contained in an electron and what is the charge of an electron?AnswerThe electron’s mass is so small that it is considered negligible when finding the mass of an atom. Electrons are negative.
88Organizing the Elements The Periodic Table17.3Organizing the ElementsPeriodic means "repeated in a pattern."In the late 1800s, Dmitri Mendeleev, a Russian chemist, searched for a way to organize the elements.When he arranged all the elements known at that time in order of increasing atomic masses, he discovered a pattern.
89Organizing the Elements The Periodic Table17.3Organizing the ElementsBecause the pattern repeated, it was considered to be periodic. Today, this arrangement is called a periodic table of elements.In the periodic table, the elements are arranged by increasing atomic number and by changes in physical and chemical properties.
90Mendeleev's Predictions The Periodic Table17.3Mendeleev's PredictionsMendeleev had to leave blank spaces in his periodic table to keep the elements properly lined up according to their chemical properties.He looked at the properties and atomic masses of the elements surrounding these blank spaces.
91Mendeleev's Predictions The Periodic Table17.3Mendeleev's PredictionsFrom this information, he was able to predict the properties and the mass numbers of new elements that had not yet been discovered.
92Mendeleev's Predictions The Periodic Table17.3Mendeleev's PredictionsThis table shows Mendeleev's predicted properties for germanium, which he called ekasilicon. His predictions proved to be accurate.
93Improving the Periodic Table 17.3Improving the Periodic TableOn Mendeleev's table, the atomic mass gradually increased from left to right. If you look at the modern periodic table, you will see several examples, such as cobalt and nickel, where the mass decreases from left to right.
94Improving the Periodic Table 17.3Improving the Periodic TableIn 1913, the work of Henry G.J. Moseley, a young English scientist, led to the arrangement of elements based on their increasing atomic numbers instead of an arrangement based on atomic masses.The current periodic table uses Moseley's arrangement of the elements.
95The Atom and the Periodic Table 17.3The Atom and the Periodic TableThe vertical columns in the periodic table are called groups, or families, and are numbered 1 through 18.Elements in each group have similar properties.
96Electron Cloud Structure The Periodic Table17.3Electron Cloud StructureIn a neutral atom, the number of electrons is equal to the number of protons.Therefore, a carbon atom, with an atomic number of six, has six protons and six electrons.
97Bohr Model PracticeIn atomic physics, the Bohr model, devised by Niels Bohr, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity
100Electron Cloud Structure The Periodic Table17.3Electron Cloud StructureScientists have found that electrons within the electron cloud have different amounts of energy.
101Electron Cloud Structure The Periodic Table17.3Electron Cloud StructureScientists model the energy differences of the electrons by placing the electrons in energy levels.
102Electron Cloud Structure The Periodic Table17.3Electron Cloud StructureEnergy levels nearer the nucleus have lower energy than those levels that are farther away.Electrons fill these energy levels from the inner levels (closer to the nucleus) to the outer levels (farther from the nucleus).
103Electron Cloud Structure The Periodic Table17.3Electron Cloud StructureElements that are in the same group have the same number of electrons in their outer energy level.It is the Number of electrons in the outer energy level that determines the chemical properties of the element.
104The Periodic Table17.3Energy LevelsThe maximum number of electrons that can be contained in each of the first four levels is shown.
105The Periodic Table17.3Energy LevelsFor example, energy level one can contain a maximum of two electrons.A complete and stable outer energy level will contain eight electrons.
106The Periodic Table17.3Rows on the TableRemember that the atomic number found on the periodic table is equal to the number of electrons in an atom.
107The Periodic Table17.3Rows on the TableThe first row has hydrogen with one electron and helium with two electrons both in energy level one.Energy level one can hold only two electrons. Therefore, helium has a full or complete outer energy level.
108The Periodic Table17.3Rows on the TableThe second row begins with lithium, which has three electrons—two in energy level one and one in energy level two.Lithium is followed by beryllium with two outer electrons, boron with three, and so on until you reach neon with eight outer electrons.
109The Periodic Table17.3Rows on the TableDo you notice how the row in the periodic table ends when an outer level is filled?In the third row of elements, the electrons begin filling energy level three.The row ends with argon, which has a full outer energy level of eight electrons.
111The Periodic Table17.3Electron Dot DiagramsElements that are in the same group have the same number of electrons in their outer energy level.These outer electrons are so important in determining the chemical properties of an element that a special way to represent them has been developed.
112The Periodic Table17.3Electron Dot DiagramsAn electron dot diagram uses the symbol of the element and dots to represent the electrons in the outer energy level.Electron dot diagrams are used also to show how the electrons in the outer energy level are bonded when elements combine to form compounds.
113Same Group—Similar Properties The Periodic Table17.3Same Group—Similar PropertiesThe elements in Group 17, the halogens, have electron dot diagrams similar to chlorine.All halogens have seven electrons in their outer energy levels.
114Same Group—Similar Properties The Periodic Table17.3Same Group—Similar PropertiesA common property of the halogens is the ability to form compounds readily with elements in Group 1.The Group 1 element, sodium, reacts easily with the Group 17 element, chlorine.The result is the compound sodium chloride, or NaCl—ordinary table salt.
115Same Group—Similar Properties The Periodic Table17.3Same Group—Similar PropertiesNot all elements will combine readily with other elements.The elements in Group 18 have complete outer energy levels.This special configuration makes Group 18 elements relatively unreactive.
116Regions on the Periodic Table 17.3Regions on the Periodic TableThe periodic table has several regions with specific names.The horizontal rows of elements on the periodic table are called periods.The elements increase by one proton and one electron as you go from left to right in a period.
117Regions on the Periodic Table 17.3Regions on the Periodic TableAll of the elements in the blue squares are metals.
118Regions on the Periodic Table 17.3Regions on the Periodic TableThose elements on the right side of the periodic table, in yellow, are classified as nonmetals.
119Regions on the Periodic Table 17.3Regions on the Periodic TableThe elements in green are metalloids or semimetals.
120The Periodic Table17.3A Growing FamilyIn 1994, scientists at the Heavy-Ion Research Laboratory in Darmstadt, Germany, discovered element 111.Element 112 was discovered at the same laboratory.Both of these elements are produced in the laboratory by joining smaller atoms into a single atom.
121Elements in the Universe The Periodic Table17.3Elements in the UniverseUsing the technology that is available today, scientists are finding the same elements throughout the universe.Many scientists believe that hydrogen and helium are the building blocks of other elements.
122Elements in the Universe The Periodic Table17.3Elements in the UniverseExploding stars, or supernovas, give scientists evidence to support this theory.Many scientists believe that supernovas have spread the elements that are found throughout the universe.
123Question 1 17.3 How are the elements arranged in the periodic table? Section Check17.3Question 1How are the elements arranged in the periodic table?
124Section Check17.3AnswerThe elements are arranged by increasing atomic number and by changes in physical and chemical properties.
125Section Check17.3Question 2What do the elements in a vertical column of the periodic table have in common?
126Section Check17.3AnswerThe vertical columns in the periodic table are called groups; elements in the same group have similar properties, such as electrical conductivity.
127Section Check17.3Question 3What do the dots in this electron dot diagram represent?
128Section Check17.3AnswerThe dots represent the electrons in the outer energy level.
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