| Term | Definition |
|---|
| Democritus | first to think of atom, stated that the atom is smallest particle of an element that retains the properties |
| Atomos | indivisible (greek) |
| Aristotle | didn't believe in atom, believed matter was continuous. Due to popularity, whole world believed him until 1700s |
| John Dalton | English chemist/school teacher. Wanted to learn in what ratios different elements combine in chemical reactions. Developed his atomic theory. Created atomic weights of elements. Law of definite and multiple proportions. |
| Dalton's Atomic Theory | 1. All matter composed of extremely small particles called atoms. 2. Atoms of a given element are identical in size, mass, and other properties. Atoms of different elements differ in these categories. 3. Atoms can't be subdivided, created, or destroyed. 4. Atoms of different elements combine in simple whole number ratios to form chemical compounds. 5. In chemical reactions, atoms are combined, separated, or rearranged. |
| Problems with Dalton's Atomic Theory | Not all atoms of an element are identical because of isotopes. They can be created/destroyed under nuclear conditions. |
| Why do atoms of different elements combine in simple whole number ratios? | You can't have part of an atom. |
| Law of definite proportions | A chemical compound contains the same elements in the same proportions no matter the size of the sample. |
| Law of multiple proportions | If 2 or more different compounds are composed of the same 2 elements, then the ratios of the elements are always in small whole numbers. |
| Formula for hydrogen peroxide | H2O2 |
| Why is hydrogen peroxide kept in dark bottles? | When exposed to light, it turns into water. |
| Atom | smallest particle of an element that can exist either alone or in combination with other atoms |
| nucleus | positively charged, dense central point of an atom that contains nearly all of the mass, but takes up a small fraction of its volume. |
| proton | subatomic particle that has a positive charge equal in strength to an electron's charge |
| electron | subatomic particle that has a negative charge equal in strength to a proton's charge. Found outside the nucleus. |
| neutron | subatomic particle that is electrically neutral |
| J.J. Thomson | discovered electron. Used cathode ray tube. |
| Plum pudding model of atom | electrons spread out in little ball of protons all together. |
| Cathode ray tube | vacuum tube w/ metal disks on each side connected by a wire to a battery. electricity jumps straight across from negative metal disk to positive. Inside, there is a screen that lets you see the stream of electrons. |
| Anode | positive end in cathode ray tube |
| Cathode | negative end in cathode ray tube |
| Robert A. Millikan | determined mass of electron using the charge to mass ratio calculated from his oil drop experiment. |
| mass of electron | 9.11 x 10 -31 kg |
| mass of proton/neutron | 1.67 x 10 -27 kg |
| charge of electron | 1.6 x 10 -19 coulombs |
| Eugene Goldstein | discovered proton using modified cathode ray tube |
| Sir James Chadwick | Discovered neutron |
| Ernest Rutherford (w/ Hans Geiger and Ernest Marsden) | Discovered nucleus of atom w/ gold foil experiment |
| Had Chadwick discovered the neutron when the gold foil experiment was done? | no |
| Alpha particles | positively charged particles |
| Gold Foil experiment | Radioactive source inside lead is shooting out alpha particles (alpha gun/beam). Most particles went right through gold. Flourescent screen is detector screen. Some particles deflected away, a few came back. Fact that most went through means there is a lot of empty space and the positive part must be small. |
| Why did none of the particles stick to the electrons in the gold foil experiment? | electrons don't stick to radiation. They only interact w/ other elements. If it did stick, that would change the substance |
| What happens when you squish metal into a thin foil? | Atoms line up and get close together but don't have multiple layers of depth. |
| Conclusion of gold foil experiment | Protons are inside nucleus, electrons are somewhere outside. |
| Bohr atom | Has circular orbits. Wrong because there are other shapes too. |
| Modern model of atom | Nucleus in middle and electron cloud outside |
| Atomic # | # of protons in nucleus of each atom of an element. Equal to electrons |
| Atomic mass | total # of protons and neutrons in nucleus |
| Isotope | atom that has same # of protons and electrons but different # of neutrons |
| Protium | Isotope of hydrogen with 0 neutrons |
| Deuterium | Isotope of hydrogen with 1 neutron |
| Tritium | Isotope of hydrogen with 2 neutrons |
| Atomic mass unit | 1/12 mass of carbon |
| When calculating atomic masses, what 3 things must you know? | # of isotopes, mass of each, % abundance of each |
| Mole | amount of substance that contains as many particles as there are atoms in 12g of C-12 |
| Molar mass | mass of one mole of a pure substance |
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