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Atoms: Building Blocks of Matter Structure of an Atom • Subatomic particles: 3 particles that make up an atom (protons, neutrons, electrons) –Nucleus: made up of protons and neutrons in center of atom Proton: positively charged particle Neutron: particle with no charge Structure of an Atom –Electrons: negatively charged particles around the nucleus All protons are alike, all neutrons are alike, and all electrons are alike even in different substances! Atomic Models Greek Model: original idea of matter made of particles –Atomos: “not to be cut” or indivisible Atomic Models John Dalton Model: 1803 All elements (gold, silver, hydrogen, oxygen,…) are made of atoms Atomic Theory and Models Dalton thought that atoms were like smooth, hard spheres that could not be broken into smaller pieces. Atomic Models Dalton Model: Atoms of the same element are exactly alike Atoms of different elements are different Atomic Models Dalton Model: Compounds: formed by the joining of atoms of 2 or more elements J.J. Thomson and his cathode ray experiment 1897 Atomic Theory and Models •Thomson suggested that atoms had negatively charged electrons embedded in a positive sphere. Also known as the “plum pudding” model Ernest Rutherford’s Gold Foil Experiment 1908 Most of the particles went directly through the foil! Atomic Theory and Models Rutherford was surprised that only a few positive particles were deflected strongly. This led him to conclude that atoms had positively charged particles in the nucleus. Atomic Theory and Models Since many particles passed right through the foil sheet, he also concluded that the atom must have a lot of space separating the nucleus from the electrons. Atomic Theory and Models Through the early twentieth century, atomic models continued to change. Niels Bohr Model: 1912 Niels Bohr suggested that electrons move in specific orbits around the nucleus of an atom Atomic Theory and Models Cloud Model: 1927 Electrons move rapidly in every direction around the nucleus Atomic Theory and Models Modern Atomic Model: The nucleus, which contains both protons and neutrons, is surrounded by a cloudlike region of electrons. • Let's see what Tim and Moby have to say about Atomic Models Design of periodic table • Periodic Table: A classification system for elements Atomic number 79 Au Gold 196.967 Atomic mass chemical symbol common name Characteristics of Atoms • Atomic Number: number of protons in each element Hydrogen = 1 Oxygen = 8 Helium = 2 Nitrogen = ___ Look at periodic table of elements in your agenda or on the back cover of your book Characteristics of Atoms • AMU: special unit to measure the mass of atoms –One proton = one AMU –One neutron = one AMU 0.00000000000000000000000167 g –Electrons have no mass 0.0000000000000000000000000911 g Using your periodic table, answer the following. How many protons does Krypton have? a) 84 b) 36 c) 83 d) 48 How many electrons does Krypton have? a) 84 b) 36 c) 83 d) 48 How many neutrons does Krypton have? a) 84 b) 36 c) 83 d) 48 Using your periodic table, answer the following. How many protons does Silver have? a) 107 b)61 c) 108 d)47 How many electrons does Silver have? a) 107 b)61 c) 108 d)47 How many neutrons does Silver have? a) 107 b)61 c) 108 d)47 Electrons • Each electron is in an energy level • The higher the energy level = the farther the distance from the nucleus • Inside level holds 2 electrons • The 2nd level holds 8 electrons • The 3rd level holds 8 electrons (it CAN hold 18) • The number of electrons in the outer “shell” or “orbit” determines how it will act and react to other substances Drawing Bohr Models of the Atom Remember the Bohr Model? Even though the “Cloud” model is the most accurate, we cannot diagram atoms easily in 3-D. We use Bohr’s model to illustrate which energy levels the electrons are located in. Examples of Bohr Diagrams Sodium • Build a Bohr Diagram Which element? Atom Game Each person represents a subatomic particle: Proton = Red Neutron = Blue Electron = Yellow In your group, please construct the following atoms – help each other! - Oxygen – O - Sodium - Na - Silicon – Si - Beryllium – Be - Chromium – Cr - Titanium - Ti Valence Electrons and Bonding Valence electrons are those electrons that have the highest energy level and are held most loosely. All elements are most stable when there are 8 electrons in their valence shell The number of valence electrons in an atom determines which elements it can bond with. • Isotopes – Atoms of the same element have the same number of protons but have different numbers of neutrons • Example of isotopes: – Hydrogen: