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Models of the Atom a Historical Perspective Early Models of the Atom • Throughout time, scientists have developed ideas about atoms. • The ideas have become more accurate over time. • For each scientist, you need to list their major contributions, or what made their model different from those that came before. Early Greek Theories •400 B.C. - All matter is made of indivisible particles called “atoms”. Democritus •Greek word “atomos” means not able to be divided. •Atom: the smallest unit of an element that maintains the properties of an element John Dalton • 1800 - Dalton proposed a modern atomic model based on experimentation not on pure reason. • All matter is made of atoms, atoms are small particles, that cannot be created, divided, or destroyed. • Atoms of an element are identical. • Each element has different atoms. • Atoms of different elements combine in constant ratios to form compounds. Adding Electrons to the Model JJ Thomson (1897) •Atoms contain negatively charged particles called electrons. •Thought that the rest of the atom must be positive. •Called the “Plum Pudding” model. (desert of choice at the time) •Electrons: negatively charged particles in an atom Ernest Rutherford (1909) Zinc sulfide screen Thin gold foil Lead block Radioactive substance path of invisible -particles • Did an experiment in which he shot alpha particles at gold foil. • Found that an atom is mostly empty space. • Found the dense, positively charged central region of the atom, called the nucleus. Nucleus in made up of protons and neutrons. Relative size of the Atom (Page 548) 1) Dalton’s “Billiard ball” model (1800-1900) Atoms are solid and indivisible. 2) Thompson “Plum pudding” model (1900) Negative electrons in a positive framework. 3) The Rutherford model (around 1910) Atoms are mostly empty space. Negative electrons orbit a positive nucleus. Bohr’s Model (1913) • Electrons are in specific paths called energy levels. •Electrons can move from one energy level to another. •The farther from the nucleus, the more energy the electrons have. Presently • Electrons do not travel in definite paths, electrons path cannot be predicted. • Electron cloud: Region around the nucleus of an atom where electrons are likely to be found. Parts of an Atom • There are 3 types of subatomic particles. • Protons: positive charge, found in nucleus • Neutrons: no charge, found in nucleus • Electrons: negative charge, found in electron clouds • Atomic mass unit: a unit of mass that describes the mass of an atom amu = .00000000000000000000000017 g • Proton: 1 amu • Neutron: 1 amu • Electron: 0 amu (1800 electrons to equal mass of 1 proton) Subatomic Particle Chart Particle Location Charge Mass Proton Nucleus +1 1 amu Neutron Nucleus 0 1 amu Electron Outside nucleus, in energy levels -1 0 Atomic Number and Mass Number • Atomic Number: The number of protons in an atom, also, the number of electrons. • Example: lithium atomic number 3 will have 3 protons and 3 electrons Mass number: total number of protons and neutrons • Example: lithium mass number 7 means 7 is the total number of protons and neutrons (3 protons and 4 neutrons) Atomic # Mass # p+ n0 e– Ca 20 40 20 20 20 Ar 18 40 18 22 18 Br 35 80 35 45 35 Energy Level Capacity Chart Energy Level 1 Maximum Number of Electrons 2 2 8 3 18 4 32 Bohr - Rutherford diagrams • Putting all this together, we get B-R diagrams • To draw them you must know the # of protons, neutrons, and electrons. • Draw protons (p+), (n0) in circle (i.e. “nucleus”) • Draw electrons around in shells He Li Li shorthand p+ 2 2 n0 p+ 3 4 n0 3 p+ 4 n0 2e– 1e– Draw Be, B, Al and shorthand diagrams for O, Na Be B Al 4 p+ 5 n° O 5 p+ 6 n° 13 p+ 14 n° Na 8 p+ 2e– 6e– 8 n° 11 p+ 2e– 8e– 1e– 12 n° Isotopes •Atoms of the same element that have different numbers of neutrons are called isotopes. •Due to isotopes, mass #s are not round #s. •H(1.00794) is made up of multiple hydrogens. 6Li 7Li 3 p+ 3 n0 2e– 1e– 3 p+ 4 n0 2e– 1e– For more lessons, visit www.chalkbored.com Periodic Table • Dmitri Medeleev • Discovered a pattern to the elements in 1869. • He wrote the names and properties of elements on cards, once he arranged the elements by atomic mass he realized a pattern. • Periodic: describes something that occurs or repeats at regualr intervals Using the Periodic Table “Groups and Periods” • Groups are Vertical Columns • Elements in same group have similar chemical properties • Elements in same group have same number of electrons in outer energy level • Ex: Lithium, group one, one electron in outer energy level • Periods are horizontal rows • Elements in same period have different chemical properties. • Elements in same period have different number of electrons in outer energy level. • Elements in same period have same number of energy levels. • Ex: lithium, period 2, 2 energy levels Types of Elements Metals • 3 or fewer electrons in outer energy level • Left side of P.T. Nonmetals Metalloids •5 or more elements that electrons in outer border the energy level zig-zag line •Right side of P.T. Similar element 13 Type of element 2 2 # of E.L. E in outer e.l. 3 7 period group neutrons electrons protons mass atomic Symbol 11 Ionic Compound Vocabulary Compound- 2 or more elements chemically joined Chemical Formula -combination of symbols and subscripts that shows what elements and how many atoms of each are in a compound, Example: Ionic Compound- compound that contains ionic bonds Ionic Bond- force of attraction between oppositely charged ions Ionic Compound Vocabulary Octet Rule –chemical rule of thumb that states that atoms tend to combine in such a way that they each have eight electrons in their valence shells, giving them the same electronic configuration as a noble gas Valence Electron – an electron found in the outermost energy level Ion- charged particle that results from a neutral atom gaining or losing electrons Polyatomic ion- 2 or more atoms that combine and act like one ion A. Naming ionic compounds made of a metal and nonmetal M-N 1. Name the metal • NaCl • Sodium chloride 2. Name the nonmetal, add –ide ending *never use prefixes • Li2O • Lithium oxide Practice 1. KCl 2. Fe2O3 3. KF 4. MgO 5. BeS 6. NaI 7. HBr 8. Sr3N2 B. Naming Compounds with Polyatomic Ions These compounds have 3 or more elements, usually a metal and a polyatomic ion • Li2 SO4 1. Name what comes first usually metal • NaOH • Lithium sulfate • Sodium hydroxide 2. Name what comes second usually PI How do Ions form? What is an ion? • A charged particle that results from a neutral atom gaining or losing electrons to become stable. Writing Balanced Formulas for Ionic Compounds 1. Write the symbols 2. Pencil in the charges 3. If the charges=0, you are finished 4. If the charges do not equal zero, balance the charges by crossing the charges to the subscripts 5. Rewrite the formula, do not write charges or subscripts of 1. • Sodium oxide • Na O • Na+1 O-2 • Na+1 O-2 • Na2O Practice Problems Strontium fluoride Cesium carbonate Sodium nitride Magnesium oxide Lithium phosphate Beryllium chlorate Calcium chloride Potassium chromate Aluminum sulfate Aluminum oxide Formula Writing • Write the correct formula for the following Ionic compounds: 1. 2. 3. 4. 5. Lithium sulfide Magnesium oxide Sodium phosphate Aluminum oxide Calcium chlorate Calculating Formula Mass of Ionic Compounds • What is formula mass? – The sum of the masses of the ions in a formula unit of an ionic compound Example Al2O3 Al 2 x 27amu= 54amu O 3 x 16amu= 48amu Formula mass= 102amu “Calculating formula mass, so easy, a Caveman could do it!” “That’s so condescending!” Covalent Compounds Vocabulary • Covalent compound- a compound containing covalent bonds • Covalent Bond- bond formed by a shared pair of electrons How do covalent compounds form? • Covalent compounds form when 2 or more nonmetals share pairs of electrons to become stable. • Electron dot diagrams are used to show the sharing of electrons. Ne He Use an electron dot diagram to show how the following covalent compounds form. H 2O H2 CH4 CO2 Ne He C. Naming Covalent Compounds (N-N) Prefix Meaning Rules Di 2 1. Name left nonmetal, use prefix if needed Tri 3 Tetra 4 Penta 5 Hexa 6 Hepta 7 octa 8 2. Name right nonmetal, use prefix if needed, add –ide Example: PBr3 Practice Problems 1. CF4 2. SCl6 3. N2O3 4. N3Br4 Writing Formulas for Covalent Compounds 1. Diphosphorous pentoxide 2. Diselenium trisulfide 3. Nitrogen trioxide 4. Carbon oxide 5. Phosphorous tetrafluoride 6. Trinitrogen hexasulfide 8. Carbon dioxide 7. Silicon dioxide 10. Carbon tetrachloride 9. Nitrogen octabromide Molecular Mass “Yes, it’s me again, and I • The sum of the masses of the atoms in covalentcan do compounds molecular • CF4 • C 1 x 12 = 12 amu • F 4 x 19= 76 amu » 88 amu mass, big deal!”