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27 Cards in this Set
- Front
- Back
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What is empirical formula?
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The simplest ratio of atoms of each element in a compound
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What are isotopes
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Molecules with the same atomic number but different mass number what
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What's the formula to calculate the number of moles
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Moles = mass/Ar
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How can you calculate the relative atomic mass
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By calculating the average of the relative isotopic masses and the relative abundance
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Why are molecules radioactive
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They have unstable nuclei
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What are the three types of emission
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Helium, beta and gamma
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Give the properties of alpha radiation
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A helium nuclei and it has a charge of (+2) and results in a nuclei having 2 fewer protons and 2 fewer neutrons it is stopped by paper/skin and has a low deflection in an electric field
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Give the properties of Beta radiation
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Electrons with a charge of (-1) and it results in nuclei having 1 more proton and 1 fewer neutron. It is stopped by aluminium foil and has a high deflection in an electric field
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What are the properties of gamma radiation
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Electromagnetic radiation and it has no charge and there's no change to the nucleus. It is stopped by lead/concrete and there's no deflection ian an electric field
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What is half life
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The time it takes for half the radioactive nuclei in a sample to decay
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What must be known to calculate the half life
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1) half life must be known accurately
2) no movement of original or new isotope 3) no resetting of radioactive clock (e.g. No heating or deformation of rocks) |
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Why should the half life of a tracer not be too short or too long
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1) it shouldn't be too short or it will decay before tracing is complete
2) or it shouldn't be to long or it will persist for too long in the body potentially causing harm to the patient |
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What is nuclear fusion
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The joining together of two or more nuclei to form a heavier nucleus
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What are the conditions for nuclear fusion
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High temperatures and/or pressure required to overcome the repulsion between two positive nuclei
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Explain atomic spectra
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An electron occupies a quantised energy level and in the ground state they have the lowest energy. In an absorption spectrum it consists of a colour spectrum with black lines corresponding to the absorption of energy by the electrons. The electron absorb a photon of energy when they become excited from heat etc... So they move up to a higher energy level (they're promoted) and the electromagnetic radiation absorbed by each of the atoms has a definite frequency (E=hv)
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What does an emission spectrum consist of
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A black background with coloured lines and the coloured lines correspond to the emissions of energy by the electrons
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Explain an emission spectrum
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Excited electrons move up to a higher energy level they are promoted so the electrons drop back to lower energy levels which produces the lines in an emission spectrum. The electromagnetic radiation emitted by each of the atoms and has a definite frequency related to the difference in energy levels but 🔼E is different for each transition so the frequency also is
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Explain electron repulsion theory
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Groups of electrons repel each other and so will arrange themselves so as to be as far apart as possible
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What is the bond angle in a tetrahedral shape
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109 for four groups of electrons
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What is the bond angle in a pyramidal or bent molecule
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109
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What is the shape of a molecule with a bond angle of 120
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Planar triangular for 3 groups of electrons
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What is the bond angle in a linear molecule?
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180
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How did Mendeleev arrange the periodic table?
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In order of relative atomic mass
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How did Mendeleev predict undiscovered elements
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He left gaps for undiscovered elements and made predictions about the properties of undiscovered elements
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How do we arrange the elements now?
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Relative atomic number
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Describe the properties of group 2
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Reactivity with water, thermal stability of carbonates, pH of hydroxide in water, solubility of hydroxide increases DOWN the group and the solubility of carbonates decrease down the group
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Describe how mass spectrometer works
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1)sample inlet: gases or liquids are simply injected but solids are heated to vaporise them
2) ionisation area: high energy electrons bombard any atoms or molecules in the sample and knock electrons out, so cations are formed 3) acceleration area: an electric field is used to accelerate any ions so they have the same kinetic energy 4) drift region there's a vacuum so that ions do not collide with air molecules and change direction 5) ion detector light ions reach the detector before heavier ones. Only positive ions are detected after fragmentation |
