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### 30 Cards in this Set

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 What does Avagadro's number tell you? The number of particles in one mole of a substance. (6.02E23) What is the empirical formula of a compound? The empirical formula tells you the simplest ratio of the atoms involved. How did Mendeleev arrange his version of the periodic table? In order of relative atomic mass, swapping elements whose chemical properties did not match and leaving gaps for elements that he predicted would be discovered. What is periodicity? Periodicity is exhibited if there is a regular pattern in a property as you go across a period and this pattern is repeated in other periods. Give three examples of periodicty. 1. Melting and boiling point. 2. Electrical conductivity. 3. Ionisation enthalpies. Define first ionisation enthalpy. The energy required to remove an electron from one mole of atoms of the element in the gaseous state. (in Kj/mol) Give the general equation for the first three ionisation enthalpies. 1. X(g) --> X+(g) + e- 2. X+(g) --> X2+(g)+ + e- 3. X2+(g) --> X3+(g)+ + e- Define an isotope. Atoms of the same element, that have the same atomic number, but a different mass number. ie different numbers of neutrons. What does the mass spectrometer tell us? It can tell us about the relative isotopic masses and the relative abundance of these isoptopes. (see picture in revision guide) What is a mass spectrum? A mass spectrum is a graph that shows the intensity of different isotopes of the same element. What makes atoms unstable? Some isotopes have unstable nuclei (ie too many protons or neutrons), resulting in it being radioactive. What are the three types of radiation? Alpha Beta and Gamma What is alpha radiation? A stream of helium nuclei, that can be stopped by paper or skin. What is beta radiation? A stream of electrons that can be stopped by aluminium foil. What is gamma radiation? An electromagnetic radiation having no effect on the mass/charge of the nucleus. It can be reduced by thick lead sheets. Define an isotope's half life. The half life is the time it takes for half the nulcei in a sample of a radioactive isotope to decay. What properties should a radioactive tracer have? It should usually emit beta radiation as this is not stopped by skin. It's half life should not be too long or it may harm the patient; or too short as it may then not be able to be detected. What is nuclear fusion? The joining of two nulcei to form a heavier nucleus. Needs high temperatures to overcome the repulsion between the nuclei. When does nuclear fusion occur? During star formation. What is an energy level? A fixed energy level that electrons can occupy. Electrons always reside in SPECIFIC energy levels. What are absoption spectra? When an electron absorbs a specific amount of energy it becomes excited and can move up an energy level. The frequency of light that it absobs is seen as a black line on a coloured background. What are emission specta? When the electron has moved up an energy level it will then move back down, releasing the same frequency of light that it absobed. Seen as a coloured line on a black bacground. What does an emission or absoption spectrum tell you? Every element has a unique absoption or emission spectrum, meaning it can be identified by it. What bond do metals and metals form? Metallic bonds: positive metal ions are arranged in a regular lattice in a sea of the delocalised electrons that come from the outer shell of the metal. What bond do metals and non-metals form? Ionic bonds: the metal atom transfers electrons to the non-metal so that all atoms have a full outer shell. The opposite charges attract (electrostatic attraction). They are held together in a giant ionic lattice. What bonds form between non-metals and non-metals? Covalent bonds: the two atoms share a pair (or more) of electrons. Represented by dot and cross diagrams. What is a dative covalent bond? This is where both of the bonding electrons come from the same atom. What bond angle do four groups of electrons result in? 109 degrees What bond angle do three groups of electrons result in? 120 degrees What bond angle do two groups of electrons result in? 180 degrees