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What do you already know about atoms? • Brainstorm about what you already know (or are pretty sure of…) about atoms. • Write it down on your paper, then we’ll discuss. What are they made of??? • Protons- Positively charged particles located in the nucleus • Neutrons- Uncharged particles located inside the nucleus • Electrons- Negatively charged particles located outside the nucleus Comparing subatomic particles… relative mass (amu) 1/1840 particle symbol electron e proton p+ 1 neutron n 0 1 - History of Atomic Models • Democritus (~400BC) – atomos = small, solid, indestructible particles of different shapes & sizes – These were just ideas, not truly science… • Dalton’s Atomic Theory – Billiard Ball Model - small solid sphere – Developed notion of conservation of mass and that atoms combine in specific ratios History of Atomic Models • J.J. Thomson – Plum Pudding Model - positive and negative particles dispersed throughout the atom – Used Cathode Ray tubes to discover the electron - first subatomic particle discovered! https://www.youtube.com/watch?v=XU8nMKkzbT8 Cathode Ray Tube • A tube that contains a stream of electrons going from a negative disk (cathode) to a positive disk. • Deflected stream showed that electrons are negative. Rutherford – Nuclear Model – Discovered dense positively charged nucleus of the atom while working with alpha particles • Gold Foil Experiment • http://www.youtube.com/watch?v=XBqHkraf8iE History of Atomic Models • Neils Bohr – Also Solar System Model – Electrons travel in specific, circular orbits • Schrodinger & Heisenburg – Quantum Mechanical Model – Dense nucleus w/ protons & neutrons – Electrons exist in ‘clouds’ called orbitals w/ specific energy levels – Mathematical predictions for probability of finding electrons – Electrons have particle and wave properties Do Now • List the three subatomic particles, their charges, and where they are located The Periodic Table Elements are so periodic ! “Repeats at regular intervals” Dimitri Mendeleev • Russian chemist • Published first version of periodic table in 1869 • Put elements in order of increasing atomic mass • All elements were not known at that time, but he was able to predict the elements that fit in the gaps. Atomic Mass Total of protons and neutrons found in the nucleus of an atom Henry Moseley Early 20th century improved the table by arranging the elements , by atomic Number (#protons) This made it more clear Which elements were missing Atomic Number Number of protons found in a nucleus, defines an atom Modern Periodic table arranged into periods 1-7 • Horizontal rows of elements – Side to side • Increase in Atomic number from left to right Li Be B C N O F Ne Families of Elements • Vertical columns of elements – Up & Down • Also referred to as Groups • Share common characteristics or properties He Ne Ar Kr Xe Rn How to read it Atomic Number Represents the number of protons in the nucleus Atomic Mass Represents the number of protons and neutrons in the nucleus 6 C 12 2 4 Electron Configuration Represents the arrangement of electrons in the energy levels of a Bohr model Symbol Represents the name of the chemical Do Now • Take out your homework….. Metals • Similar in many properties – Luster/Shiny – Malleable (can be pressed into sheets) – Conduct heat and electricity – Ductile (can be drawn out into wires) Nonmetals – Usually gases or brittle solids – Most are poor conductors of heat and electricity – Most are gases at room temperature Metalloids • Have some properties of both metals and nonmetals • Along the stair step • Ex: boron has luster but is a • Poor conductor of electricity Green – metals Yellow – nonmetals Blue - metalloids Do Now • Use your NEW periodic tables to find the following information for Oxygen • Atomic Number • Atomic Mass • Number of Protons • Number of Electrons • Number of Neutrons Structure of an atom: • Nucleus: –Protons + –Neutrons 0 • Electrons - Electrons • Some electrons are closer to the nucleus than others. • The closer to the nucleus the greater the attraction, therefore the harder to remove. Bohr Diagram • The Bohr model, introduced by Niels Bohr in 1913, • 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 Electron Energy Stairwell • Nucleus is the ground floor. • Electrons closest to the nucleus are the first floor, they are held most tightly. • The next sphere is the second floor and so on. • The first level is also the smallest it can hold 2 electrons. • Second floor is larger and can hold 8 electrons • Third floor can hold 18 electrons • Fourth floor can hold 32 electrons Hydrogen 1H Your Bohr Atomic Mass = 1 - Atomic # = 1 # neutrons = 0 1 Atomic # = # protons = 1 # protons = 1 # neutrons = 0 # electrons = # protons = 1 1 NOTE: There are no neutrons in a Hydrogen atom! Helium 4He Your Bohr Atomic Mass = 4 - Atomic # = 2 # neutrons = 2 2 Atomic # = # protons = 2 # protons = 2 # neutrons = 2 2 NOTE: The first level of Helium is full! # electrons = # protons = 2 Lithium 7Li Your Bohr Atomic Mass = 7 Atomic # = 3 # neutrons = 4 3 Atomic # = # protons = 3 # protons = 3 # neutrons = 4 # electrons = # protons = 3 2 1 NOTE: The first energy level is full, so the 3rd electron goes to the next energy level! Beryllium 9Be Your Bohr Atomic Mass = 9 - Atomic # = 4 # neutrons = 5 4 Atomic # = # protons = 4 # protons = 4 # neutrons = 5 # electrons = # protons = 4 2 2 NOTE: There are 2 electrons on the outer energy level! Boron 11B Your Bohr Atomic Mass = 11 - Atomic # = 5 # neutrons = 6 5 Atomic # = # protons = 5 # protons = 5 # neutrons = 6 # electrons = # protons = 5 2 3 NOTE: There are 3 electrons on the outer energy level! Magnesium 24Mg Your Bohr Atomic Mass = 24 - Atomic # = 12 # neutrons = 12 12 Atomic # = # protons = 12 # protons = 12 # neutrons =12 2 8 2 NOTE: The outer level has 2 electrons! # electrons = # protons = 12 Aluminum 27Al Your Bohr Atomic Mass = 27 - Atomic # = 13 # neutrons = 14 13 Atomic # = # protons = 13 # protons = 13 # neutrons =14 # electrons = # protons = 13 2 8 3 NOTE: There are 3 electrons in the outer energy level! Silicon 28Si Your Bohr Atomic Mass = 28 - Atomic # = 14 # neutrons = 14 14 Atomic # = # protons = 14 # protons = 14 # neutrons =14 # electrons = # protons = 14 2 8 4 NOTE: There are 4 electrons in the outer energy level! Phosphorous Your Bohr Atomic Mass = 31 - Atomic # = 15 31P 15 # neutrons = 16 Atomic # = # protons = 15 # protons = 15 # neutrons =16 # electrons = # protons = 15 2 8 5 NOTE: There are 5 electrons in the outer energy level! Sulfur Your Bohr Atomic Mass = 32 - Atomic # = 16 32S 16 # neutrons = 16 Atomic # = # protons = 16 # protons = 16 # neutrons =16 # electrons = # protons = 16 2 8 6 NOTE: There are 6 electrons in the outer energy level! Chlorine 35Cl Your Bohr Atomic Mass = 35 - Atomic # = 17 # neutrons = 18 17 Atomic # = # protons = 17 # protons = 17 # neutrons =18 # electrons = # protons = 17 2 8 7 NOTE: There is room for only one more electron in the outer energy level! Argon Your Bohr Atomic Mass = 40 - Atomic # = 18 40Ar 18 # neutrons = 22 Atomic # = # protons = 18 # protons = 18 # neutrons = 22 2 8 8 NOTE: All three energy levels are full! # electrons = # protons = 18 Welcome Back!!! Do Now Group Period 2 4 17 5 13 4 6 6 Element Name Element Symbol P (+) N (0) E (-) Chemical Activity • Since the electrons on the inner shells are buried they cannot leave the atom. • Which would be the only electrons that can detach from the atom? • The one in the last layer! • They are also the most loosely attached to the nucleus because they are so far away. Valence Electrons: The electrons in the outer most energy level • To determine the valence electron number look at the periodic table. Group # # Valence electrons 1 1 2 2 3-12 Usually 2 13 3 14 4 15 5 16 6 17 7 18 8* (He 2) … or look at the box on the periodic table Electron Configuration 6 C 12 2 4 Valence electrons are the last number Dot Diagrams • Dot diagrams are used to show the number of valence electrons. • Carbon = 4 valence electrons C • Practice: Write the electron dot diagrams for the following elements. • Magnesium Oxygen • Nitrogen Cesium • Tin Argon • Aluminum Helium Do Now • • • • • • • Take out your homework to be checked Draw Dot Diagrams of the following elements: He Hg Ar Pb P Fe O W N I Chemical Bonding • All chemical reactions involve the movement of valence electrons forming or breaking chemical bonds to form a Compound. • Compound: Molecule made of two or more elements. Magic Number • The Magic Number- 8(or 0) valence electronsatoms bond to get a full valence shell. • The last shell wants to be full to be stable! How can chlorine get another Electron to become stable? Ionic Bonds • Ionic Bonds- forms between a metal and a nonmetal. Electrons are moved from one atom to the other. What happens if valence electrons are transferred? • Electrons are exchanged between objects, giving them a charge. Metals • • • • • Metals have 1,2 or 3 valence electrons. Will they give or get electrons? GIVE! It’s easier to give away a few than to get a lot. If metals give away electrons will they become positive or negative? •+ positive Non Metals • • • • Nonmetals have 5 or more electrons. Will they give away or take electrons? TAKE It’s easier for them to take a few than to give away a lot. • Will they become positive or negative? •- negative IONS • Ion- electrically charged atom formed when electrons move during reactions • + ion- Cation formed when electrons are lost • – ion- Anion formed when electrons are gained DO NOW • What is an ion? • An electrically charged atom formed when electrons move during reactions • What is an ionic bond? • A bond between a metal and a nonmetal • When forming an ion do metals become positive or negative? Nonmetals? • Metals give electrons and become positive • Nonmetals receive electrons and become negative Oxidation Number • The charge that the ion gets when it either loses or gains electrons is called the oxidation number. The sum of the oxidation numbers for the atoms in a compound must be zero In order for a compound to exist, it must be electrically neutral NaCl Sodium loses one electron so it has an oxidation number of 1+ Na 1+ Chlorine gains one electron so it has an oxidation number of 1- Cl 1- This works because 1(1+) + 1(1-) = 0 The sum of the oxidation numbers for the atoms in a compound is zero Li2O Lithium loses one electron so it has an oxidation number of 1+ Li 1+ Oxygen gains two electrons so it has an oxidation number of 2- O 2- This works because 2(1+) + 1(2-) = 0 The sum of the oxidation numbers for the atoms in a compound is zero Do now • Determine the formula of a compound formed from: • Na and Cl • Ca and S • Au and O • Al and S Criss-Cross Method Shortcut The ‘criss-cross’ method is a simple way of determining a formula The oxidation number of one element becomes the subscript of the other Li +1 and O -2 ‘Criss - Cross’ Method The formula for the compound composed of potassium and sulphur K 1+ & S 2This becomes K2S The formula for the compound composed of calcium and bromine Ca 2+ & Br 1This becomes CaBr2 Steps to follow • Step 1- write element symbols with the metal first • Step 2- write the oxidation numbers next to the elements • Metals = valence electron number (with a (+) sign) • Nonmetals = (valence electron #) – 8 • Step 3- criss-cross numbers without signs • Step 4- don’t write 1’s for final compound • Step 5- reduce the numbers. ‘Criss-Cross’ Method Practice Using Oxidation Numbers, write formulas for the compounds formed from the following elements Sodium & Bromine Potassium & Iodine Calcium & Fluorine Hydrogen & Sulfur Magnesium & Fluorine Lithium & Sulfur Remember to check that the sum of the oxidation numbers is equal to zero! NaBr KI CaF2 H2S MgF2 Li2S DO NOW • What is the formula of the compound formed when copper and sulfur combine? Naming Compounds Binary Compounds are composed of two elements Binary Compounds are named beginning with the element with the positive oxidation number (The Metal) The name of the second element will end in an ide NaCl : Sodium Chloride CaS : Calcium Sulfide FeO : Iron Oxide Name the Compound • • • • • • 1. Potassium + Nitrogen 2. Magnesium + Arsenic 3. Gallium + Phosphorous 4. Indium + Iodine 5. Barium + Fluorine 6. Aluminum + Oxygen Covalent Bonds • A bond between two nonmetals. • Electrons are shared instead of transferred to make the compound stable. ex: H + H H2