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Gen Chem chapt 2
atoms and the periodic table
| Question | Answer |
|---|---|
| Dalton's Atomic Theory. | 1) elements are composed of atoms. 2) atoms of same element are identical, but differ from other elements. 3) elements can mix together 4) atoms only change when mixed with other elements |
| cathode rays | Radiation (electron beams) emitted from the negatively charged plate in an evacuated tube when a high voltage is applied. |
| a cathode ray moves toward. | the positively charged plate (anode) to produce a bright light |
| Columb's Law | like charges repel, opposites attract |
| Mass of an electron | charge/ charge or mass = -1.6022e^-19 / -1.76e8 =9.10e-28 |
| William Roentgen | discovered x-rays in 1895 |
| radioactivity | The spontaneous emission of radiation by an unstable atomic nucleus |
| in order to be neutral, an atoms must... | contain something positively charged |
| In thomsons model | the positive charge of an atom was so diffuse that the relatively massive positive a particles should have all passed through the foil (plum pudding model) but actually didn't |
| Rutherford | Gold foil experiment, discovered nucleus |
| for an atom to be neutral.. | it must contain the same number of protons and neutrons |
| the number of neutrons | mass number - atomic number (A-Z) |
| isotopes | Atoms that have the same atomic number (Z) but different mass numbers (A) |
| density tells us | how closely the particles are packed |
| the stability of the nucleus.. | is determined by the difference between coulombs repulsion and the short-range attraction the factor that determines that a nucleus is stable is the neutron to proton ratio (as the atomic number increases, the ratios of stable nuclei also increase) |
| belt of stability | The principal factor for determining whether a nucleus is stable is the neutron to proton ratio. |
| ions | positively and negatively charged atoms |
| how many sig figs for atomic mass | 5 to 6 sig figs |
| metal | Elements that are good conductors of heat and electric current. |
| Nonmetal | an element that is a poor conductor of heat and electricity |
| Metalloid | Elements that have properties of metals and non-metals. May be good conductors of electricity or heat depending on the situation. |
| metalloid elements | B, Si, Ge, As, Sb, Te, Po |
| halogens | Group 7A |
| Chalcogens | Group 6A |
| very few atoms exist as isolated atoms | those that do are noble gases |
| mol | amount of substance that contains as many elementary entities |
| alpha particle (a) | A helium ion with a positive charge of +2 |
| beta particle | an electron |
| gamma rays | high-energy radiation |
| molar mass (M) | The mass in grams of 1 mole of a substance |
| nucleons | protons and neutrons |
| define atom | Basic unit of matter |
| name the types of radiation known to be emitted by radioactive elements | -Alpha particles. -Beta particles. -Gamma rays. -Neutrons. |
| compare the properties of alpha particles, cathode rays, protons, neutrons, and electrons | alpha particles: is composed of 4 neutrons and 2 electrons and protons cathode rays: streams of electrons produced from a cathode. protons: positively charged neutrons: no charge electron: negatively charged |
| JJ Thomson | discovered the electron |
| Milikan | oil drop experiment; determined the charge of an electron |
| James Chadwick | Discovered the neutron |
| why does the atomic number enable us to deduce the number of electrons present in an atom? | because an atom is electrically neutral and must contain equal numbers of electrons as protons. |
Created by:
landryw
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