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Elements, Atomic Structure, and Atomic Models Physical Science Mrs. Baker Chemical Symbols • Capitals matter! • Element symbols contain ONE capital letter followed by lowercase letter(s) if necessary. Metal that forms bright blue solid compounds. Co vs. CO Poisonous gas. History of Atomic Theory (or how do we study atoms?) • How can we study atoms? They are so SMALL!!! • Over time, scientists have invented several experiments to help increase our understanding of atoms. • A scientific model is a representation of an object or event that makes it easier to understand things that are difficult to observe directly. – Example: Solar system mobile – Example: Atomic theories The Structure of an Atom • Nucleus—small, dense, positively charged central portion of the atom – Protons – neutrons • Area outside of the nucleus – Electrons Subatomic Particles • Protons – Positively charged (assigned charge of +1) – Mass of 1 – Found in nucleus • Electrons – Negatively charged (assigned charge of -1) – RELATIVELY no mass – Found outside of nucleus • Neutrons – Existence proven by James Chadwick in 1932 – Mass of 1 – Neutral particle (0 charge) – Found in nucleus + - Secton 4.2 – The Structure of an Atom Comparing Subatomic Particles • Protons, electrons and neutrons are distinguished by – Mass – Charge – Location inProperties an atom of Subatomic Particles Particle Symbol Electron Proton Neutron e + p n - Relative Charge 1 + 1 0 Relative Mass (Proton = 1) 1/1836 1 1 Actual Mass (g) 9.11E-28 1.67E-24 1.68E-24 Secton 4.2 – The Structure of an Atom Atomic Number and Mass Number • Atomic number – Atoms of any given element always have same number of protons – Atoms of different elements always have different number of protons – Atomic number of an element = # of protons in one atom of that element – Atoms are neutral, so each proton in an atom (with its positive charge) is balanced by one electron (with a negative charge); thus, atomic number also equals number of electrons • Mass number – Mass number of an atom = # of protons + # of neutrons in nucleus of that atom – Number of neutrons = Mass number – Atomic number Mass Number • Sum of the protons and neutrons in the nucleus of an atom. ♦ Always a whole number. © Addison-Wesley Publishing Company, Inc. ♦ # of neutrons = mass # - atomic # Secton 4.2 – The Structure of an Atom Isotopes • All atoms of an element have the same number of protons • NOT ALL atoms of an element have the same number of neutrons • Isotopes of an element: atoms of the same element that have different numbers of neutrons, and thus different mass numbers • Isotopes are referred to by their name and mass number when needed (example: hydrogen-1 and hydrogen-2) • Example: heavy water is made up of two hydrogen-2 atoms bound to oxygen Isotopes © Addison-Wesley Publishing Company, Inc. Subatomic Particles ATOM NUCLEUS NUCLEUS ELECTRONS ELECTRONS PROTONS PROTONS NEUTRONS NEUTRONS POSITIVE POSITIVE CHARGE NEUTRAL NEUTRAL CHARGE Most of the atom’s mass. NEGATIVE CHARGE NEGATIVE CHARGE in a neutral atom Atomic Number equals the # of... Subatomic Particles • Quarks – 6 types • 3 quarks = 1 proton or 1 neutron He Atomic Structure Timeline A basic history of our understanding of the atom. Democritus (400 B.C.) • Proposed that matter was composed of tiny indivisible particles • Not based on experimental data • Greek: atomos Alchemy (next 2000 years) • Mixture of science and mysticism. • Lab procedures were developed, but alchemists did not perform controlled experiments like true scientists. John Dalton (1807) • British Schoolteacher – based his theory on others’ experimental data • Billiard Ball Model – atom is a uniform, solid sphere Secton 4.1 – Studying Atoms Dalton’s Atomic Theory • 5 Parts of Dalton’s Theory: 1) All elements are composed of atoms 2) All atoms of the same element have the same mass, and atoms of different elements have different masses 3) Compounds contain atoms of more than one element 4) In a particular compound, atoms of different elements always combine the same way 5) Atoms cannot be divided. Henri Becquerel (1896) • Discovered radioactivity – spontaneous emission of radiation from the nucleus • Three types: – alpha (α) - positive – beta (β) - negative – gamma (γ) - neutral J. J. Thomson (1903) • Cathode Ray Tube Experiments – beam of negative particles • Discovered Electrons – negative particles within the atom • Plum-pudding Model J. J. Thomson (1903) Plum-pudding Model – positive sphere (pudding) with negative electrons (plums) dispersed throughout Ernest Rutherford (1911) • Gold Foil Experiment • Discovered the nucleus – dense, positive charge in the center of the atom • Nuclear Model Ernest Rutherford (1911) • Nuclear Model – dense, positive nucleus surrounded by negative electrons Niels Bohr (1913) • Bright-Line Spectrum – tried to explain presence of specific colors in hydrogen’s spectrum • Energy Levels – electrons can only exist in specific energy states • Planetary Model Bohr’s Model of the Atom • Focused on electrons – Electrons move with constant speed in fixed orbits around the nucleus – Each electron has a specific amount of energy – Energy levels: the possible energies that electrons can have – No two elements have the same set of energy levels • An electron in an atom can move from one energy level to another when an atom gains or loses energy • Evidence for energy levels: Light given off in fireworks Niels Bohr (1913) Bright-line spectrum • Planetary Model – electrons move in circular orbits within specific energy levels Erwin Schrödinger (1926) • Quantum mechanics – electrons can only exist in specified energy states • Electron cloud model – orbital: region around the nucleus where e- are likely to be found Erwin Schrödinger (1926) Electron Cloud Model (orbital) • dots represent probability of finding an enot actual electrons James Chadwick (1932) • Discovered neutrons – neutral particles in the nucleus of an atom • Joliot-Curie Experiments – based his theory on their experimental evidence James Chadwick (1932) Neutron Model • revision of Rutherford’s Nuclear Model