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3/22/2012 Chapter 3 Lecture Presentation Introductory Chemistry Fourth Edition Chapter 3 The Evolution of Atomic Theory © 2011 Pearson Education, Inc. 3.1 Dalton’s Atomic Theory • Atoms proposed around 400 B.C. – Took 2000 years to be accepted • Dalton’s atomic model (early 1800s) formulated explanations for a variety of laws. © 2011 Pearson Education, Inc. 3.1 Dalton’s Atomic Theory (Continued) • Law of conservation of mass – When a reaction takes place, matter is neither created or destroyed. © 2011 Pearson Education, Inc. 1 3/22/2012 3.1 Dalton’s Atomic Theory (Continued) • Law of constant proportions – Multiple samples of any pure compound always contain the same percent by mass of each element making up the compound. © 2011 Pearson Education, Inc. 3.1 Dalton’s Atomic Theory (Continued) • Percent by mass – Consider that 50.0 g of water (H2O) is decomposed into the component elements yielding 5.6 g of H and 44.4g of O2. What is the percent by mass of the components? – It is always the same for pure water. © 2011 Pearson Education, Inc. 3.1 Dalton’s Atomic Theory (Continued) • Dalton’s atomic theory 1. 2. 3. 4. 5. All matter is made up of atoms. Atoms can neither be created nor destroyed. Atoms of a particular element are alike. Atoms of different elements are different. A chemical reaction involves the union or separation of individual atoms. © 2011 Pearson Education, Inc. 2 3/22/2012 3.1 Dalton’s Atomic Theory (Continued) • Ball-and-hook model – Different size balls represent different atom types. – Different types have different numbers of hooks representing bonding. © 2011 Pearson Education, Inc. 3.1 Dalton’s Atomic Theory (Continued) • No point of the theory is entirely true, so updates have occurred. – Atoms are not the most fundamental unit. • Protons, electrons, and neutrons – Atoms can be created and destroyed in nuclear reactions. • Although updates were needed, it does not diminish the theory or its usefulness. © 2011 Pearson Education, Inc. 3.2 Development of a Model for Atomic Structure • What do atoms look like? – Problem tackled by J.J. Thomson, James Chadwick, and others – Found atoms are comprised of even smaller particles. © 2011 Pearson Education, Inc. 3 3/22/2012 3.2 Development of a Model for Atomic Structure (Continued) • J.J. Thomson – In 1897, he discovered the electron. • The first subatomic particle – Very small and lightweight • 1/1836 mass of a hydrogen atom – Has a negative charge, which is referred to as negative one © 2011 Pearson Education, Inc. 3.2 Development of a Model for Atomic Structure (Continued) • J.J. Thomson and E. Goldstein – In 1907, they discovered the proton. – Much heavier than the electron • Mass is roughly equal to a hydrogen atom. – Exhibits a positive charge referred to as positive one © 2011 Pearson Education, Inc. 3.2 Development of a Model for Atomic Structure (Continued) • James Chadwick – 25 years later, he discovered the neutron. – Roughly same mass as a proton – Did not exhibit a charge • Was electrically neutral – Very difficult to study due to the absence of charge © 2011 Pearson Education, Inc. 4 3/22/2012 3.2 Development of a Model for Atomic Structure (Continued) Properties of Subatomic Properties © 2011 Pearson Education, Inc. 3.2 Development of a Model for Atomic Structure (Continued) How could these subatomic particles lead to the variety of the periodic table? © 2011 Pearson Education, Inc. 3.2 Development of a Model for Atomic Structure (Continued) How could these subatomic particles lead to the variety of the periodic table? By containing differing numbers of each subatomic particles, the elements of the periodic table exhibit differing behaviors. © 2011 Pearson Education, Inc. 5 3/22/2012 3.2 Development of a Model for Atomic Structure (Continued) • The first model proposed by J.J. Thomson is called the plum-pudding model. – Knew two basic facts: 1. Atoms contain small, negatively charged particles. 2. Atoms of an element behave as if they have no charge. – Reasoned that something must encapsulate the negative charge of the electron – Proposed a “cloud of positive electricity” © 2011 Pearson Education, Inc. 3.2 Development of a Model for Atomic Structure (Continued) Plum-Pudding Model © 2011 Pearson Education, Inc. 3.3 The Nucleus • Rutherford’s gold foil experiment – Fired alpha particles at metal foils • Alpha particle has two protons and two neutrons with a charge of +2. • Gold foil is only a couple of thousand atoms thick. – Used a glass substrate covered with zinc sulfide to monitor the alpha particles – Expected a straight flight path for the particles © 2011 Pearson Education, Inc. 6 3/22/2012 3.3 The Nucleus (Continued) • Results were almost the expected. • While most flew straight through, some bent or were “bounced” backward. © 2011 Pearson Education, Inc. 3.3 The Nucleus (Continued) • This non-linear flight was very unexpected. • Rutherford’s quote: “It was … as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.” © 2011 Pearson Education, Inc. 3.3 The Nucleus (Continued) • From the study, he knew two things: 1. Most of the alpha particles went straight through the foil. • Most of the atom must be empty space. 2. A few of the alpha particles (about 1 in 20,000) were deflected from a straight-line path. • • There must be a small and massive something inside the atom. This massive unit must have a positive charge. © 2011 Pearson Education, Inc. 7 3/22/2012 3.3 The Nucleus (Continued) • Rutherford’s model of the atom – An atom is mostly empty space. • Contains the electrons spread throughout the atom – A nucleus is a tiny, massive, positively charged unit in the atom. • Placed in the center of the atom • Contains the protons and neutrons © 2011 Pearson Education, Inc. 3.3 The Nucleus (Continued) Rutherford’s Model of the Atom © 2011 Pearson Education, Inc. 3.3 The Nucleus (Continued) • Why don’t opposite charges simply collapse into each other? • Rutherford knew more work was needed. • Ended in a new form of physics – Quantum physics was born. © 2011 Pearson Education, Inc. 8 3/22/2012 3.4 The Structure of the Atom • What we know: – The nucleus at the center of the atom contains: • Protons—relatively massive and positively (+1) charged • Neutrons—relatively massive and neutrally charged – Electrons orbit the nucleus with a -1 charge. – Positive and negatively charged atoms are drawn to one another. © 2011 Pearson Education, Inc. 3.4 The Structure of the Atom (Continued) © 2011 Pearson Education, Inc. 3.4 The Structure of the Atom (Continued) • Atomic number (Z) – The number of protons in the nucleus – Determines the identity of the atom – The atom with one proton is always hydrogen. © 2011 Pearson Education, Inc. 9 3/22/2012 3.4 The Structure of the Atom (Continued) • Mass number – Number of protons plus the number of neutrons © 2011 Pearson Education, Inc. 3.4 The Structure of the Atom (Continued) Sketch a neutral carbon atom in the following three ways, showing the correct numbers of protons, neutrons, and electrons. (a) Make the mass number equal to 12. (b) Make the mass number equal to 13. (c) Make the mass number equal to 14. © 2011 Pearson Education, Inc. 3.4 The Structure of the Atom (Continued) © 2011 Pearson Education, Inc. 10 3/22/2012 3.4 The Structure of the Atom (Continued) • Isotopes – Atoms with the same number of protons (same element), but different numbers of neutrons – Exhibit identical chemical properties © 2011 Pearson Education, Inc. 3.4 The Structure of the Atom (Continued) • Isotope symbol – Shows both the mass number and the atomic number along with the element symbol 12 6 C – Often, the atomic number is omitted as it is implied by the element symbol. © 2011 Pearson Education, Inc. 3.4 The Structure of the Atom (Continued) • Isotopes – All isotopes are not present in the same amounts. • 12C = 98.89%, 13C = 1.11%, and 14C = trace amounts – Nearly all elements have isotopes. • Hydrogen has three isotopes with special names. © 2011 Pearson Education, Inc. 11 3/22/2012 3.4 The Structure of the Atom (Continued) 1. Identify an atom with a mass number of 16, containing 9 neutrons. 2. Give the full atomic symbol for an atom with 16 neutrons and an atomic number of 15. © 2011 Pearson Education, Inc. 3.4 The Structure of the Atom (Continued) © 2011 Pearson Education, Inc. 3.4 The Structure of the Atom (Continued) • Atomic mass – The actual mass of any atom – Have units of atomic mass units (amu) or daltons (Da) – Relative atomic mass • Measures how massive an atom is in comparison to a 12C atom • 1H would be 1/12 the mass of 12C. © 2011 Pearson Education, Inc. 12 3/22/2012 3.4 The Structure of the Atom (Continued) • Weighted average of atomic mass – Values reported on the periodic table – Weighted average of the isotope masses • 14C is ignored due to its only having trace amounts present. © 2011 Pearson Education, Inc. 3.5 The Law of Mendeleev—Chemical Periodicity • By 1860, nearly 70 elements had been isolated and studied. • As discovered, a means to organize the elements was needed. • Enter Mendeleev and his arrangements © 2011 Pearson Education, Inc. 3.5 The Law of Mendeleev—Chemical Periodicity (Continued) • A major breakthrough occurred when the elements were ordered by increasing atomic mass • He noticed a regular repeating of properties – Every eighth element exhibited similar properties. – K, Na, and Li for example © 2011 Pearson Education, Inc. 13 3/22/2012 3.5 The Law of Mendeleev—Chemical Periodicity (Continued) • K, Na, and Li all: – React vigorously with water – Form oxides (K2O) and hydroxides (KOH) – Are conductive © 2011 Pearson Education, Inc. 3.5 The Law of Mendeleev—Chemical Periodicity (Continued) • Law of octaves – Elements that are eight elements apart by mass react in similar manners. – Called chemical periodicity or periodic behavior © 2011 Pearson Education, Inc. 3.5 The Law of Mendeleev—Chemical Periodicity (Continued) • Law of Mendeleev – Properties of the elements recur in regular cycles (periodically) when elements are arranged in order of increasing atomic mass. © 2011 Pearson Education, Inc. 14 3/22/2012 3.5 The Law of Mendeleev—Chemical Periodicity (Continued) • Gaps in Medeleev’s table – He left gaps for undiscovered elements in his table. – He predicted the properties of the missing elements. © 2011 Pearson Education, Inc. 3.5 The Law of Mendeleev—Chemical Periodicity (Continued) • Predicted values matched those in the later found elements • Giving further support to his arrangement of elements © 2011 Pearson Education, Inc. 3.6 The Modern Periodic Table • Current organization of the 113 elements • Elegant and simplistic in showing information • Relays both subatomic structures and chemical properties • Shows the atomic number and mass for each element © 2011 Pearson Education, Inc. 15 3/22/2012 3.6 The Modern Periodic Table (Continued) • Periods of the periodic table – The horizontal rows of the table – Numbered 1 through 7 as you descend © 2011 Pearson Education, Inc. 3.6 The Modern Periodic Table (Continued) • Groups – The vertical columns of the table – Also called families – Numbered in a few different manners: • Using roman numerals • Using Arabic numbers – Groups with varying names are shown in violet. © 2011 Pearson Education, Inc. 3.6 The Modern Periodic Table (Continued) © 2011 Pearson Education, Inc. 16 3/22/2012 3.6 The Modern Periodic Table (Continued) • Sections of the table – Main-group elements—groups 1, 2, and 13−18 • Much early chemistry based here • Shows strongest periodic nature – Transition metals—groups 3−12 – Lanthanides (rare earths) and actinides • In the lower section of the table, not numbered © 2011 Pearson Education, Inc. 3.6 The Modern Periodic Table (Continued) • Transition-metal numbering – Numbered with roman numeral and B – I and II are at the high end of the B numbers. – This awkwardness leads to the adaption of the 1-through-18 numbering scheme. © 2011 Pearson Education, Inc. 3.6 The Modern Periodic Table (Continued) • Phase of matter at room temperature – Solid, liquid, and gas – Group 18 elements are the noble gases. © 2011 Pearson Education, Inc. 17 3/22/2012 3.6 The Modern Periodic Table (Continued) • Metallic nature – Metal, nonmetal, or metalloid – Separated by stair-step starting at boron – Roughly 75% are metals. – All life is based on the nonmetal carbon. © 2011 Pearson Education, Inc. 3.6 The Modern Periodic Table (Continued) • Metals – Shiny solids – Bendable and malleable • Nonmetals – Brittle – Do not conduct electricity or heat well • Semimetals – Can act as a metal or nonmetal © 2011 Pearson Education, Inc. 3.6 The Modern Periodic Table (Continued) 1. How many groups constitute main-group elements? 2. What do the groups of the periodic table have in common with one another? © 2011 Pearson Education, Inc. 18 3/22/2012 3.6 The Modern Periodic Table (Continued) © 2011 Pearson Education, Inc. 3.6 The Modern Periodic Table (Continued) • Group names – Five common names used – The first two and last three columns © 2011 Pearson Education, Inc. 3.6 The Modern Periodic Table (Continued) • Law of octaves adjustments – Works well when only considering the maingroup elements – After row 4, repeats after 18 spaces • Due to inclusion of transition metals – After row 6, increases again to 32 elements • Due to inclusion of lanthanides and actinides • We will return to this topic in later chapters. © 2011 Pearson Education, Inc. 19 3/22/2012 3.7 An Introduction to Ions and the First Ionization Energy • Atoms are neutral due to balanced numbers of protons and electrons. • Ions are when this balance is not present. – Either an electron is added or removed. © 2011 Pearson Education, Inc. 3.7 An Introduction to Ions and the First Ionization Energy (Continued) • Ions – Negatively charged ions are anions. – Positively charged ions are cations. © 2011 Pearson Education, Inc. 3.7 An Introduction to Ions and the First Ionization Energy (Continued) • Ion notations – Charges are shown as superscripts after symbol. – + and – are used to show positive and negative charges – For +1 and -1, the one is generally implied. – Any element written without charge is neutral. © 2011 Pearson Education, Inc. 20 3/22/2012 3.7 An Introduction to Ions and the First Ionization Energy (Continued) • First ionization energy – Minimum amount of energy it takes to completely remove an electron forming +1 ion – Always requires energy to overcome coulombic attractions © 2011 Pearson Education, Inc. 3.7 An Introduction to Ions and the First Ionization Energy (Continued) • First ionization energy – Exhibits periodicity similar to chemical properties – Metals exhibit lower values than nonmetals. • Metals like to give up electrons. • Nonmetals like to gain electrons. © 2011 Pearson Education, Inc. 3.7 An Introduction to Ions and the First Ionization Energy (Continued) • Looking ahead – Rutherford’s model cannot explain the periodicity seen. – An improved model is needed. • Hint: Comes from light spectra © 2011 Pearson Education, Inc. 21 3/22/2012 3.7 An Introduction to Ions and the First Ionization Energy (Continued) • Sunlight – Exhibits a continuous spectra – All colors are seen and blend together. • Light from elements – Exhibits a line spectra – Not all colors are seen and there are distinct breaks in spectra. © 2011 Pearson Education, Inc. 22