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History Democritus named the most basic particle atom- means “indivisible” Aristotle didn’t believe in atoms thought matter was continuous (thought you could keep dividing it) Ch. 3: Atoms 3.1 Foundations History by Law of Conservation of Mass 1700s, all chemists agreed: mass is neither created or destroyed during regular chemical or physical changes on the existence of atoms that atoms combined to make compounds Still did not agree on whether elements combined in the same ratio when making a compound Law of Definite Proportions Law of Multiple Proportions any amount of a compound contains the same element in the same proportions by mass No matter where the copper carbonate is used, it still has the same composition applies when 2 or more elements combine to make more than one type of compound the mass ratios of the second element simplify to small whole numbers helped to emphasize the idea of atoms 15.9994 15.9994 15.9994 15.9994 31.9988 1 Law of Multiple Proportions Dalton’s Atomic Theory All matter is made of atoms Atoms of same element have the same size, mass, and properties Atoms can’t be subdivided, created or destroyed Atoms of different elements combine in whole number ratios to make compounds In chemical reactions, atoms can be combined, separated, and rearranged. 1. 2. 3. 4. 5. Modern Atomic Theory Some parts of Dalton’s theory were wrong: atoms are divisible into smaller particles (subatomic particles) atoms of the same element can have different masses (isotopes- atoms of the same type with different masses) Most important parts of atomic theory: all matter is made of atoms atoms of different elements have different properties Ch. 3: Atoms 3.2 Structure of Atom Structure of Atom Nucleus: contains protons and neutrons takes up very little space contains most of the particles Electron Cloud: contains electrons takes up most of space Subatomic Particles includes all particles inside atom proton electron neutron charge on protons and electrons are equal but opposite to make an atom neutral, need equal numbers of protons and electrons 2 Subatomic Particles number of protons identifies the atom as a certain element protons and neutrons are about same size electrons are much smaller nuclear force- when particles in the nucleus get very close, they have a strong attraction Atomic Radius size of atom from center of nucleus to outside of electron cloud really is one-half the distance between the center of two identical nuclei bonded together expressed in picometers (1012 pm = 1 m) usually 40-270 pm proton + proton proton + neutron neutron + neutron 3