114 named atoms – Periodic table ATOMIC THEORY Atoms are the basic building blocks of matter. First suggested by Democritus about 400 BC. 114 named atoms – Periodic table

Early Greek Theories Democritus thought matter could not be divided indefinitely. This led to the idea of atoms. 350 B.C - Aristotle modified an earlier theory that matter was made of four “elements”: earth, fire, water, air. This idea was dead wrong.

Parts of the Atom The Nucleus is the center of the atom Has all of the positively charged protons as well as the neutrons which has no charge. Is the dense central portion that occupies a small fraction of the volume. The Electron Cloud Region around the nucleus that contains the negatively charged electrons. Orbitals are specific regions in the electron cloud where the electrons move. Orbitals are also called electron cloud because they have no boundary.

Essential Questions – Structure of the Atom 1. Name the 3 important sub-atomic particles and indicate their symbol, charge, and mass. 2. Identify the location of these subatomic particles. Protons Neutrons Electrons

Name, Symbol, Charge, Location & Mass of the Subatomic Particles 1. Electrons (e) have a one negative charge (-1) and are located in the electron cloud. Mass of an electron = 9.109 x 10 – 31 kg 2. Protons( p) have a one positive (+1) located in the nucleus. Mass of a proton = 1.673 x 10 – 27 Kg 3. Neutrons (n) have no charge ( 0 ) and are also located in the nucleus. Mass of a neutron = 1.675 x 10 – 27 kg.

Essential Question #3 Explain the role of the electrons in understanding and studying chemistry?

The Importance of Electrons in Chemistry Electrons determine how an element will react with other elements. Electrons differentiate between chemical and nuclear reactions. Electrons are key in defining chemical properties Defining physical properties, Understanding the structure of molecules and compounds.

Essential Question # 4 How is the identity of an element determined?

The Identity of an Element Determined by the Atomic Number Which Is the identification number Represents the number of protons in the nucleus The protons do not participate in a chemical reaction. Their amount stays the same. It also reveals the number of electrons which are identical to the number of protons It is recognized by whole number on the periodic table which is one of the two numbers that characterizes an atom.

Essential Question #5 How is the mass of the element determined?

The Mass Number tells the sum of the protons and neutrons. The Mass of the Atom is determined 1. By the Average Atomic Mass 2. By the Mass Number The Average Atomic Mass of an element is determined by the averaging the masses of that element’s Isotopes. It is recognized by the larger decimal number on the periodic table of elements. When the Average Atomic Mass is rounded off to a whole number it is called the MASS NUMBER. The Mass Number tells the sum of the protons and neutrons. The number of neutrons is determined by subtracting the atomic number from the mass number. ( # n = Mass Number – Atomic Number)

What are Isotopes? Isotopes are defined as the atoms of an element that have a different number of neutrons but the same number of protons as the normal element. Therefore the mass of each isotope is different from the mass from the normal atoms. The number of isotopes vary from element to element. Hydrogen has 3 isotopes H-1; H-2; H-3 Lead has 4 isotopes: Pb -204; Pb -206; Pb – 207; Pb- 208.

How are Isotopes different from the Normal Atoms of a given Element? Isotopes have a different mass from the normal atoms. The mass information of each isotope can only be obtained from a reference table. But the mass of the normal atom is listed on the periodic table as the Average Atomic Mass. The mass of Normal Atom of any element is determined by calculating the average of the masses of that element’s isotopes according on their relative abundance in a given sample.

Two Types of Symbols Nuclear Symbol Hyphen Notation Nuclear Symbol is used to represent the atomic number and the average atomic mass as seen on the periodic table. Ex: The Nuclear Symbol for Oxygen is O 815.99 has 8 protons; 8 electrons; 8 neutrons Hyphen Notation indicates the symbol of the element and its mass number only. Ex: For Oxygen 8 15.99 the hyphen notation is O - 16

Name all the key factors needed to describe the atom of an Element? 1.The atomic number 2. Average atomic number 3. The mass number 4. The # of protons and their charge 5. The # of electrons and their charge 6. The # of neutrons and their charge 7. The name and symbol The Nuclear Symbol 8. Hyphen Notation

Section Review p. 78 # 1- 6 Omit #5 P. 89 # 1- 6 Practice Decoding Atomic Number, Mass Number P. 86 Practice # 1 – 4 P. 89 practice # 1- 2 Dalton’s Atomic Theory p. 78

Chemical Laws That Support the Chemical Behavior of the Atom as Proven by Experimentation 1. The Law of Definite Proportion – John Proust - 1797 2. The Law of Conservation of mass- Antoine Laurent Lavoisier -1782 3. The Law of Multiple Proportions – Claude –Louis Berthollet – 1790. 4. Dalton’s Atomic Theory - 1808 ( not a law)

Dalton’s Atomic Principles 1. All matter is composed of extremely small particles called atoms which cannot be subdivided, created or destroyed.( later revised because of the discovery of sub- atomic particles) 2. Atoms of a given element are identical in their physical and chemical properties (later revised because of the discovery of isotopes) 3. Atoms of different elements differ in their physical and chemical properties – ( Still True) 4. Atoms of different elements combine in simple whole number ratios to form compounds – (also stated in the law of Multiple Proportion and less so in the Law of Definite Proportion) – Today many atoms also can combine with atoms like themselves ex: O2, Cl 2 etc., 5. In a Chemical Reaction atoms are combined , separated, or rearranged but never created, destroyed or change- ( also stated in the Law of Conservation of Mass)

Law of Definite Proportion The law of Definite Proportion states that 2 samples of a given compound are made of the same elements in exactly the same proportion by mass regardless of the SIZE or SOURCES of the samples. Ex: All sample sizes of NaCl ex. 5.0 g or 24.0 g will contain - 60.66 % Chlorine 39 .34 % Sodium Ex: All samples sizes of Ethylene Glycol will contain the same percentage of each elements – Oxygen, Carbon, Hydrogen 51.56 % Oxygen 38.70 % Carbon 9.4 % Hydrogen

Law of Conservation of Mass The law states that the mass of the reactants in a reaction are equal to the mass of the products: ( see page 76) For the Chemical Reaction Sulfur + Oxygen = Sulfur Dioxide S + O2 = SO2 The Masses are as follows: 5.325 x 10-26 kg + 5.314 x 10-26 kg = 1.064 x 10-25 kg +

Proof of the Law of Conservation To prove the Law: sum the mass of Reactant #1 to Mass of Reactant #2 Show that the mass of the sum of the reactants is the same mass as the product Reactant #1 + Reactant #2 = Product Sulfur atom + Oxygen Molecule = Sulfur Dioxide Molecule Reactants Sulfur = 0. 5325 x 10 -25 kg Reactant Oxygen = 0.5314 x 10 -25 kg = 1. 059 x 10-25 kg which is similar to the Mass of Sulfur Dioxide 1.064 x 10 -25 kg

Law of Multiple Proportions States that if two or more different compounds are composed of the same elements; the ratio of the masses of the second element which combines with a given mass of the first element is always a simple whole number ratio. Ex: Carbon Monoxide - CO - 1 C: 1 O Carbon Dioxide - CO2 - 1 C : 2 O Nitrogen monoxide - N 0 - 1 N : 1O Nitrogen Dioxide - NO2 - 2 N : 2 O

Homework & Review 1. Page 86 answer the practice questions- Atomic Number and Mass Number # 1 – 4. 2. Page 89 answer review questions - # 1- 5 3. Decode the atomic number and mass number of elements # 1- 20 for protons ,neutrons, and electrons, nuclear symbol, hyphen notation. Record the information in a convenient chart chart. 4. Copy and stud the 5 Principles of Dalton’s Atomic Theory p. 78

Discovery of the Electron – J. J Thomson The electron – discovered by J.J. Thomson using a cathode-ray tube CRT (p. 80 figure 6) He pumped air in the tube. He applied a voltage between the negative electrode and the positive anode. He observed a glowing beam that came out of the negative electrode He called the beams Cathode Rays. The rays were deflected when a magnet was brought close to them - He assumed that the rays had a negative charge since they came form the negative electrode. - He called the negative rays electrons.

Thomson Plum Pudding Model Since atoms are electrically neutral Thomson concluded that there are also positive particles that balance the negative electrons. He thought that the negative electrons were imbedded in a ball with positive charge – page 81, figure 7 He named his atomic model the “Plum Pudding Model”

Discovery of the Nucleus & Protons by Ernest Rutherford Rutherford discovered the nucleus of the atom His discovery was made through the “Gold Foil Experiment” p. 81 – figure 8. He shot a beam of alpha Particles through a thin sheet of Gold Foil. They measured the angle of deflection of the beams as they came out of the foil. He found that most of the Alpha particles passed through the foil without deflection. He reasoned that most of the atom was empty space Only a very small percentage was deflected & repelled by a dense positive mass. He called this dense core the Nucleus. He argued that the Positive Alpha Particles were repelled by Protons which also had a positive Charge. The Charge of the proton is exactly opposite to the electron = +1

Discovery of the Neutron James Chadwick discovered and named the neutron Neutrons are not deflected by electric and magnetic fields. Neutrons have no charge and act as shields that prevent the protons from repelling each other. Neutrons are located in the nucleus

Key terms 1. Nucleus 12. Dalton’s Atomic Theory 2. Electron Cloud 13. Average Atomic Mass 3. Orbital 14. Mass Number 4. Sub-atomic particles 15. Isotopes 5. Electron 16. Atomic Models 6. Proton 17. J. J. Thomson 7. Neutrons 18. Earnest Rutherford 8. Elementary Particles 19. James Chadwick 9. Law of Definite proportions 20 . Curie 10. Law of Multiple Proportions 11. Law of Conservation of Mass

Practice Exercises Page 78 # 7 – Definite Proportion Page 107 # 13 (Conservation of Mass) Page 78 # 9 – (Multiple Proportion) – Copy Table 1 Page 77

Home Work – 10/22/10 1. Copy and label following apparatuses used by each scientist in the discovery of each of the three subatomic particles. 2. Briefly describe how each scientists used their apparatus to make the discovery a) J.J. Thompson – Cathode Ray tube experiment –figure 6 Page 80 b) Rutherford –Gold Leaf Experiment - Figs 8a &*b – page 81

Unit used for Atomic Mass p.100 - 104 Atoms are so small that the gram is not a convenient unit for measuring their mass. Instead a special Unit the Atomic Mass Unit (amu) is used to express ATOMIC MASS. The Atomic Mass Unit is the same as the Mass Number since each proton each neutron has a mass of about 1 amu . Examples: 1. The isotope Cu – 63 has an Atomic Mass of 63 amu 2. The atom P 15 30.973 has an Atomic Mass of 30.973 amu

Practice with Atomic Mass Express the Atomic Mass for each of the following atoms in Atomic Mass Units (amu). 1. Mg 2. Ca 3. Ar 4. O 5. Ba

How do Scientists go about counting a great number of atoms? They invented a new and convenient unit called the mole.

How is the Mole defined? A mole in SI unit is defined as the number of atoms in exactly 12 grams of carbon-12. The mole is the SI unit for the amount of a substance Chemist use the mole as counting units just as you use the dozen as a counting unit. Instead of asking for 12 eggs, you ask for a dozen eggs. Similarly chemists refer to 1 mol of carbon and 2 mol of iron.

What is the Equivalent Moles in grams Chemist use the term MOLAR MASS when working with moles. The MOLAR MASS of an element is the mass in grams of one mole of an element. The MOLAR MASS is numerically equivalent to to an elements atomic mass. The UNITS for the MOLAR MASS is grams/mol (g/mol). For example the Atomic Mass of copper is 63.55 amu, the MOLAR MASS of Copper is 63.55g/mol

Practice Molar Mass p. 102 practice # 1-4 # 1. What is the mass in grams of 1 mol of Uranium ? Solution: 238 g of U makes 1 mol # 2. What is the mass in grams of 0.0050 mol of Uranium? 0.0050 mol x 238g U = 1.2 g 1 mol U

What is the exact number of atoms in 1 mol of any substance? Scientists have determined that the exact number of particles present in one mol of a substance is called the Avogadro’s Number. The Avogadro Number contains 6.022 x 10 23 particles. In Chemistry the word particle is used interchangeably with atoms, molecules and ions.

About how large a number is 6.022 x 1023 ? Image that every living person on Earth started to count the number of atoms in 1 mol of carbon. If each person counted nonstop at a rate of one atom per second, it would take over 3 million years to count every atom.

Practice counting particles p. 103 Practice 1-3 #1. How many atoms are in 0.70 mol of Iron? Solution 0.70 mol Fe x 6.022 x 10 23 atoms of Fe = 4.2 x 1023 atoms 1 mol of Fe #2. How many moles of silver are represented by 2.888 x 10 23 atoms?