Topic 1. Edexcel Chemistry A level Questions and Answers

Topic 1. Edexcel Chemistry A level Questions and Answers What is atomic number? -The number of protons in the nucleus of an atom of an element. -All atoms of the same element have the same number of protons. What is the mass number? The total number of protons and neutrons in the nucleus of an atom of an element. What is an isotope? - Atoms of an element with the same number of protons but a different number of neutrons. - Same proton number but different mass number. What affects the physical properties of an isotope? -Mass of atom affects physical properties, so isotopes will have slightly different physical properties e.g. different densities, rates of diffusion. What affects the chemical properties of an isotope? -Number and arrangement of electrons determine the chemical properties, so isotopes have the same chemical properties. What is the relative atomic mass? - Ar, is the AVERAGE mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12. - not usually a whole number. What is the relative isotopic mass? - The mass of an atom of an isotope, compared to 1/12th of the mass of an atom of carbon-12. - usually a whole number. What is the relative molecular mass? - Average mass of a molecule compared to 1/12th of the mass of an atom of carbon-12. What is the relative formula mass? - Average mass of a formula unit compared to 1/12th of the mass of an atom of carbon-12. Difference between RMM and RFM? RMM: used when referring to simple molecules. Find RMM by adding the RAM of all the atoms in the molecule. RFM: used for ionic compounds (or giant covalent e.g SiO2). To find RFM, add up RAM of all the ions or atoms in the formula. How to calculate relative atomic masses from isotopic abundances? 1. Multiply the relative isotopic mass by its % relative isotopic abundance. 2. Add the products together. Divide by 100 (as its % abundance) How to use mass spectrometry to work out relative atomic masses? 1. Multiply the relative isotopic mass by its relative isotopic abundance. (not % abundance) 2. Add up the results. 3. Divide by the sum of the isotopic abundances. How to calculate isotopic mass from relative atomic mass? (if you are given 2 out of 3) 1. Work out the abundance of the final isotope (if you don't know it). 2. Use the formula for calculating RAM from RIM & % relative isotopic abundance. 3. Rearrange the formula to work out the isotopic mass of the missing element. How to predict the mass spectra for diatomic molecules? 1. Express the abundances as decimals. 2. Create a table showing all the possible molecules that could be formed. 3. For each molecule, multiply the decimal abundances of the isotopes to get the relative abundance of each one. 4. Look for molecules in the table that are the same, if they are, add up their abundances. 5. Divide all the relative abundances by the smallest relative abundance to get the smallest whole number ratio. 6. Use the RMM of the molecules to predict the mass spectrum. What are the steps in Mass Spectrometry? 1. Vaporisation 2. Ionisation 3. Atomisation 4. Deflection 5. Detection How to use mass spectra to identify compounds? - to find the RMM of a compound, look at the molecular ion peak (M peak). - the m/z value is the molecular mass of the compound, you can use this to predict the compound. What are electrons grouped together in? - quantum shells (energy levels) How many electrons can each quantum shell hold? - !st quantum shell: 2 electrons. 2nd quantum shell: 8 electrons. 3rd quantum shell: 18 electrons. 4th quantum shell: 32 electrons. What are the 4 different subshells? - s, p, d, f What is an orbital? - a region of space around the nucleus of an atom which can hold up to 2 electrons with opposite spin. -there's a 95% chance of finding electrons. How many orbitals are in each subshell? s subshell: 1 orbital. p subshell: 3 orbitals. d subshell: 5 orbitals. f subshell: 7 orbitals. What is the maximum number of electrons an orbital can hold? 2 What shape is the S orbital? spherical What shape is the P orbital? dumbell shape Arrows in boxes configuration? What does it represent? - represents electrons spinning in opposite directions. What is Aufbau's principle for electron configuration? Electrons will fill in the orbital and subshells with the lowest available energy level first. What is Hunds rule for electron configuration? Electrons will occupy the orbitals singly before pairing takes place. What is Paulis exclusion principle? Each orbital holds up to 2 electrons, and for electrons to occupy the same orbital they must have an opposite spin. What two subshells don't follow this rule? The 4s and 3d subshell. What is the electron configuration for ions? - for positive ions, subtract the number of electrons. - for negative ions, add the number of electrons. What are the two exceptions to electron configuration? Copper Chromium What are the s block, p block, d block elements? - s block: Group 1&2. p block: Group 3-7, 0. d block: transition metals. What is the emission spectra? - In the ground state atoms have electrons in their lowest possible energy levels. - If an atoms electrons take in energy, electrons get excited and move to a higher energy level, which is further away from the nucleus. - Electrons release energy by dropping from higher to lower energy levels. What does the emission spectrum show? - Emission spectrum shows frequencies of light emitted when electrons drop from a higher energy level to a lower energy level. - Energy levels have fixed values. How does emission spectra support the idea of Quantum shells? Emissions correlate with the energy of each quantum shell What is ionisation? The removal of one or more electrons from an atom. What is the first ionisation energy? - the energy required to remove one electrons from 1 mole of gaseous atoms to produce 1 mole of gaseous ions with one positive charge. What are successive ionisation energies? The energy required remove one electron from 1 mole of gaseous +1 ions to produce 1 mole of gaseous ions with a +2 charge What three factors affect Ionisation Energy? Shielding, Nuclear charge and Electron shells How does shielding affect ionisation energy? As the number of electrons between the nucleus and the outer electrons increases, the less attraction felt by the outer electrons— this is shielding. How does nuclear charge affect ionisation energy? The more protons in the nucleus, the more positively charged the nucleus is. This means there's a stronger the attraction for the electrons. How does electron shells affect the ionisation energy? The greater the distance of he electron from the nucleus, the weaker the electrostatic attraction. Why are successive ionisation energies greater than the previous ones? - After the first electron is removed, positive ion is formed. - means theres a strong electrostatic attraction on the remaining electrons - more energy is required to overcome the attraction. What is the trend in ionisation energy down a group? - Decreases. - increase in atomic radius. - Extra energy level, so electron is further away from the nucleus. - less attraction between electrons and nucleus so electron is more easily lost. How does successive IE show shell structure? - within each shell, the successive ionisation energy increases. Electrons are being removed from an increasingly positive ion - means there is less repulsion so electrons are held together more strongly -there are also jumps in the ionisation energy where electron is removed from a new shell closer to the nucleus. What is periodicity? - the repeating pattern of physical and chemical properties.