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Transcript
Interpreting Chemical Formulas 02 • Atoms!! • http://www.brainpop.com/science/matterandch emistry/atoms/preview.weml 02 • A Chemical Formula uses symbols and numbers to represent the composition of a pure substance. 02 • The chemical formula for water represents: – The composition of water wherever it is found. The chemical formula for water is always the same! – The composition of a molecule of water. The chemical formula tells us that a water molecule s made up of 3 atoms; 2 hydrogen and 1 oxygen. 02 Symbol for the element hydrogen The small number here means 2 atoms of hydrogen. Symbol for the element Oxygen No small number means 1 atom of oxygen 02 • The atomic number of an element provides information about its atomic structure. • For example, the atomic number of fluorine is 9, indicating that there must be 9 protons in the nucleus. 02 • On its own the atomic number does not tell us the number of neutrons in an element. In order to determine the number of neutrons we need the mass number. 02 • The proper notation for writing about the structure of an atom uses both the mass number and the atomic number. 02 • The atomic masses in the periodic table are stated in atomic mass units (u). An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. Na 11 protons 11 electrons Na+ 11 protons 10 electrons anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. Cl 17 protons 17 electrons Cl- 17 protons 18 electrons
