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Download Standard Atomic Notation 17 35 mass # atomic
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Review: Inside the Atom atoms consist of subatomic particles protonspositively charged electronsnegatively charged neutronsneutral the number of protons is significant since it is this that determines what the element actually is atomic number = number of protons number of protons = number of electrons number of neutrons = mass number number of protons a charged atom is called an ion electrons are very small and can be stripped off easily since each proton balances each electron, the ion has a charge equal o the number of electrons it has lost +1 Example: Na has lost one electron Standard Atomic Notation mass # 35 17 Cl Hint mass # Na atomic # Hint atomic # 1 Developing Models of Matter What does an atom look like? How do the 'pieces' fit together? First some history... About 450 BC • Greek Philosopher Empedocles • Earth, Air, Wind, Fire About 400 BC • Democritus • matter made of tiny particles • called them atoms About 350 BC • Aristotle • very influential because he was educated • Empedocles model accepted for nearly 2000 years AD 5001600 • Alchemistspart philosopher, mystic, magicion and chemist • developed many of our current procedures and tools but still accepted the 4 element model • attempted to make gold of cheap materialsdid not succeed! 2 About 1650 • Robert Boyle • developed a new definition for "element" • " a pure substance that cannot be broken down into simpler substances" About late 1700's • Priestly, Lavoisier and Cavendish • isolated oxygen and later hydrogen and recognised them as elements • Priestlyisolated oxygen • Lavoiserrecognized Oxygen was an element and air is a mixture • Cavendish found that acid+metal=Hydrogen 1808 • John Dalton Particle Theory All matter is made of tiny particles Each element has its own kind of atom and mass Compounds are created when elements combine atoms cannot be created or destroyed 3 1800's • 1831Michael Faraday matter must contain positive and negative charges opposite charges attract, like charges repel atoms combine to form compounds because of electrical attractions • Found electric current causes chemical changes to some compounds 1904 • JJ Thomson • "raison bun" model atoms contain particles called electrons electrons are very small and negative remainder is a sphere with a positive charge electrons are "embedded" in this sphere, resulting in an uncharged atom • Discovered electron • Experimented with protons Draw diagram!! 4 1911 • Ernest Rutherford • gold foil experiment a tiny dense positive core called the nucleus surrounded by mostly empty space containing the rapidly moving negative electrons A Planetary Model of the Atom Niels Bohr, suggested the following: electrons can move around the nucleus in nearly circular orbits each electron has a specific amount of energy the farther away from the nucleus the greater the amount of energy electrons cannot exist 'between' these orbits, butcan move up and down from one orbit to another the order of filling these orbits is 2, 8, 8 for the the first three orbits electrons are more stable at lower energy, closer to the nucleus 5 Bohr Diagrams the element symbol is written in the center and the electrons are 'filled' into the orbits around this nucleus Electron Example: Hydrogen has 1 proton, so 1 electron H Nitrogen has 7 protons and so has 7 electrons (Hint: remember 2,8,8) N 6 Try these! determine the # of protons and electrons Dont forget the 2, 8, 8 Electron P Cl Mg F BohrRutherford diagrams combination of Rutherford’s nuclear model & Bohr’s planetary model circle in middle to represent nucleus of the atom number of protons & neutrons are written here electrons shown in circular orbits Ex. Carbon 7 You Try! Helium Nitrogen Sulfur Sodium 8
