Basic Laws and Important People Intro to Chemistry

Fundamental Chemical Laws 1. Law of Conservation of Mass States that matter cannot be created or destroyed Its just rearranged through chemical processes Total mass of reactants must be equal to the total mass of the products

2. Law of Definite Proportion A given compound always contains the same proportions of elements by mass Compounds do not have a changing form Compounds have a fixed ratio of components

Law of Multiple Proportions When two elements form a series of compounds (Homologous series in organic) the ratio of masses of the elements can always be reduced to the smallest whole number Also it is important to note that sometimes two elements can produce a series that is not able to be reduced CO, CO2, CO3, etc…

ImPortant people and what they did Early Experiments to Characterize the Atom ImPortant people and what they did

J.J Thomson and Electrons Determined the charge to mass ratio of the electron - 1.76 x 108 C/g Reasoned that all atoms must contain at least 1 electron Reasoned that atoms must have a positive charge as well although he didn’t “find” the particle Used the cathode ray tube experiment to determine this information

Robert Milikan and the oil drop Used this experiment to determine the magnitude of the charge of an electron Along with Thomson he determines the mass of an electron to be 9.11 x 10-31 kg

Radioactivity Gamma Rays Beta Particles Alpha Particles

Rutherford and the Gold Foil Experiment Uses this experiment to determine that all atoms are composed of mostly empty space All atoms also have a positive dense core that he calls a nucleus Makes an attempt to develop an atomic model but was incorrect with his placement of particles Considered the ground breaking experiment in the fields of chemistry and physics with regards to atoms

2.5 Modern View of The Atom 1. Nucleus---center of mass Contains protons and neutrons Positive charge that is indicated by the atomic number of an element Small size, large density 2. Electrons Source of reactivity Negative charge 1/2000th the mass of a proton

Parts of an atom Continued 3. Atomic Number– same as number of protons Identifying feature of all elements Number cannot be changed for an individual atom 4. Mass Number Protons + Neutrons Can be different for isotopes of the same element Number on periodic table is a weighted average of all known isotopes for the element

Parts…. 5. Isotopes----same element with a different number of neutrons Gives this version a different mass

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