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All Chem Definitions
Chemistry Leaving Cert Chap 2-24
| Question | Answer |
|---|---|
| Dalton's atomic Theory | Summarised. 1. All matter is made up of very small particles called atoms 2. All atoms are indivisible They cannot be broken down into simpler particles. |
| Cathode Rays | Streams of negatively charged particles called electrons. They travel in straight lines from the cathode to anode, are deflected by electric and magnetic fields, and have sufficient energy to move a small object such as paddle wheel. |
| Who came up with the concept of the atom? | One of the most important Greek philosophers, Democritus believed that the tiny particles could not be broken down, were indivisible, hence 'atomos' the Greek word for indivisible was used as their name |
| Energy Levels | The fixed energy value that an electron in an atom may have. |
| Ground Level | Lowest available of energy that an electron can occupy. |
| Excited state | Where an electron can occupy a higher energy in an electron. This state of energy is higher than ground state. |
| Heisenberg's Uncertainty Principle | States that it is impossible to measure at the same time both the velocity and position of an electron. |
| Orbital | A region in a space within which there is a high probability of finding an electron. |
| Energy Sublevels | A subdivision of the main energy level and consists of one or more orbitals of the same energy. |
| Element | A substance that cannot be split into simpler substances by chemical means. |
| What are the Triads and who came up with them? | Triad: group of threes elements with similar chemical properties in which the atomic weight (relative atomic mass) of the middle element is approx equal to the average of the other two. Johann Doberiner came up with the idea of Triads. |
| What are octaves and who came up with them? | Octaves: arrangements of elements in which the first and eighth element, counting from a particular element, have similar properties. John Newlands |
| Mendeleev's Periodic Law | When elements are arranged in order of increasing atomic weight (relative atomic mass), the properties of the elements recur periodically. |
| Atomic Number | Number of protons in the nucleus of the atom |
| Modern Periodic Table | Arranged by increasing atomic number |
| Modern Periodic Law | Elements in increasing atomic number, properties reoccurring periodically |
| Mass Number | Sum of protons and neutrons in the nucleus |
| Isotopes | Atoms of the same element with different mass numbers due to different neutron numbers |
| Relative Atomic Mass | Average no. of the isotopes of the element as they occur naturally, taking into account, their abundance, expressed on a scale in which the C-12 atom has 12 units |
| Principle of Mass Spectrometry | VIASD Vaporisation Ionisation Acceleration Separation Detection |
| Electron Configuration | Shows arrangement of electrons in an atom of an element |
| Aufbau Principle | When building up the electron configuration of an atom in its ground state the electrons occupy the lowest available energy levels |
| Hund | When two or more orbitals of equal energy are available, the electrons occupy them singly before filling them as pairs |
| Pauli's | no more than two electrons may occupy an orbital and they must have opposite spin. |
| Compound | Is a substance that is made up of two or more different elements that are chemically combined |
| Octet Rule | When bonding occurs, atoms tend to create an electron arrangement where there are eight electrons in the outermost shell / energy level. |
| Ion | Charged atom or groups of atoms |
| Ionic Bonding | Force of attraction between two oppositely charged ions in a compound. Ionic bonds are always formed by the complete electron transfer from one atom to another. |
| Transition Metals | Forms at least one ion with a partially filled d sublevel |
| Molecule | Group of atoms formed together the smallest part that can exist independently. |
| Valency | Valency of an atom is defined as the number of atoms of hydrogen or any other monovalent element with which each atom of the element combines |
| Sigma Bond | Head on overlap of two orbitals |
| Pi Bond | Sideways overlap of p orbitals |
| Electronegativity | Relative attraction that an atom in a molecule has for a shared pair of electrons in a covalent bond. |
| Polar covalent Bond | A bond that has unequal sharing of the pair(s) of electrons, causing one to be positive and the other to be negative. |
| Ionic Bonding | Greater than 1.7 |
| Polar Covalent | Less than or equal to 1.7 |
| Non- polar Covalent | Greater than 0.4 and less than 1.7 |
| Intramolecular Bonding | Takes place within a molecule |
| Intermolecular | Forces of attraction between molecules |
| Van der Waals | Weak attractive forces between molecules resulting from the temporary dipole formation only found between non polar molecules. |
| Dipole-Dipole | Forces of attraction between the negative pole of one polar molecule and the positive of another. |
| Hydrogen bonds | Dipole-dipole bond with hydrogen when bonded to nitrogen, fluorine or oxygen. |
| Law of Conservation of mass | Total mass of products in a chemical reaction must = total mass of reactants. |
| Law of Conservation of Matter | Matter is neither created or destroyed, but simply turns from one form to another |
| Atomic Radius | Half the distance between the nuclei of two atoms of the same element, joined together by a single covalent bond |
| Atomic Radii increasing | Atomic Radii increase down the groups. This is due to new energy levels and decrease in screening effect. |
| Atomic Radii decreasing | Atomic Radii decrease across periods due to increasing effective nuclear charge adn decreasing atomic radius. |
| Second Ionisation Energy | The energy required to remove an electron from an ion with a positive charge in a gaseous state. |
| Electronegativity increase and decrease | Decreases down groups and increases across periods. Opposite to Atomic Radii |
| Radioactivity | Spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation. |
| Nuclear reaction | The process that alters the composition, structure or energy of an atomic nucleus |
| Half Life | The time it takes for the half of a nuclei in any given sample decay |
| Radioisotope | A radioactive isotope |
| Radiocarbon Dating | Use of the half life of C12 and or C14 |
| Mole | One mole of a substance is that amount of substance that contains 6x10^23 particles of that substance. |
| One mole of an Element= | Relative Atomic mass in grams e.g. 12 grams of Carbon. |
| Relative molecular mass (Compound) | The average mass of one molecule of that compound compared with 1/12th of the C12 atom. |
| Mass of one mole of a compound = | Relative molecular mass the grams |
| Gas | A substance with no well defined boundaries but diffuses rapidly into any container it is placed in. |
| Standard Temperature | 273 Kelvin = 0 degrees Celsius |
| Standard Pressure | 1x10^5 Pa = 100 kPa |
| Boyle's Law | At a Constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure. |
| Charles' Law | At constant pressure, the volume of a fixed mass of gas is directly proportional to temperature in Kelvin |
| Gay-Lussac's Law | In a reaction between gases the volumes of the reacting gases and the volumes of any gaseous are in the ratio of small whole numbers provided the volumes are measured at the same temp and pressure. |
| Avogadro's Law | Equal volumes of gases contain equal number of molecules under the same conditions of temperature and pressure |
| Avogadro's Law | Equal volumes of gases contain equal number of molecules under the same conditions of temperature and pressure |
| Ideal Gas | Perfectly obeys all the assumptions of kinetic theory of gases under all conditions of temperature and pressure. |
| Ideal Gas | Perfectly obeys all the assumptions of kinetic theory of gases under all conditions of temperature and pressure. |
| Real Gases | |
| Avogadro's Law | Equal volumes of gases contain equal number of molecules under the same conditions of temperature and pressure |
| Ideal Gas | Perfectly obeys all the assumptions of kinetic theory of gases under all conditions of temperature and pressure. |
| Real Gases | Differs from ideal gases because : 1 forces of repulsion and attraction . 2. Volume of molecules are not negligible |
| Molecular Formula | is a type of formula which shows the number and type of each atom present in a molecule. |
| Empirical Formula | is a type of formula showing the simplest whole number ratio of the different atoms in a molecule |
| Arrhenius definition: Acid | Acid is a substance that dissociates in water to produce H+ ions. Strong dissociates almost completely. Weak acids only dissociates partially |
| Arrhenius definition: Base | Base is a substance that dissociates in water to produce OH- ions. Strong base dissociates almost fully in water. Weak bases only dissociate partially |
| Bronsted-Lowry acid | Good proton donor |
| Bronsted-Lowry base | Good proton acceptor |
| Conjugate Base | Acid -> conjugate base when donating |
| Conjugate Acid | Base -> conjugate acid when accepting |
| Conjugate Acid-Base Pair | Any pair consisting of an acid and a base that differ a proton |
| Salt | Substance formed when the H ion from an acid |
| Neutralisation | Reaction between an acid and base to form a salt and water |
| Solution | A completely perfect mixture of solute and solvent in a solution the particles of the solute are uniformly distributed throughout the solvent. |
| Concentration | The amount of solute dissolved in a given volume of solution |
| Molarity | Number of moles of solute/solution |
| Standard Solution | Standard Solution is where the concentration of the solution is accurately known |
| Primary standard | A substance that can be obtained in a stable, pure and soluble solid form so that it can be washed out and dissolved in water to give a standard solution. |
| Titration | A Lab procedure where a measured volume of one solution is added to a measured volume of another solution, until the reaction is complete. The completion of a reaction is shown using an indicator. |
| Oxidation | Where an element loses electrons |
| Reduction | Where an element gains electrons |
| Oxidation Agent | Brings about oxidation in a substance |
| Reducing Agent | Brings about reduction in a substance |
| Oxidation number | The charge that an atom has or appears to have when electrons are distributed according to certain rules |
| Rate of Reaction | Rate of reaction at any one particular time, of any given product or reactant in a reaction |
| Catalyst | A substance that increases the rate of reaction by creating an alternative energy pathway |
| Enzyme | Biological catalyst |
| Homogenous Catalyst | Reactants and Catalyst are in the same phase |
| Heterogenous Catalyst | Reactants and Catalyst are in different phases |
| Autocatalysis | Products of a reaction are the catalyst for the reaction |
| Catalytic converters | Device that converts harmful gases to slightly softer ones |
| Catalyst Poison | A substance that inhibits a catalyst e.g. Lead poisons catalytic converters |
| Activation Energy | The amount of energy required for a successful collision, resulting in products, to occur. |
| Reversible Reactions | When reactions can go forwards and backwards |
| Chemical equilibrium | State of dynamic balance in a reversible where forward rate = reverse rate |
| Dynamic State | Reactants continuously form as products who continuously form |
| Le Chatlier's | Stress applied to a system at equilibrium will adjust to relieve stress |
| Acid Base Indicator | Substance that changes colour depending on the pH its placed in |
| Range of an Indicator | The pH over which the indicator can change colour |
| Hard Water | Water that doesn't Lather because of the presence of Ca2+ or Mg2+ ions |
| Temporary Hardness | Can be removed by boiling water to get rid of Mg or Ca ions |
| Permanent Hardness | Cant be removed by boiling water. |
| Floccation | Coagulation of suspended particles |
| Flocculating Agent | Chemical added to water to coagulate suspended particles thus helping sedimentation take place |
| Screening | Water is passed through wire meshes to remove larger objects |
| Sedimentation / Settlement | Water flows into settlement tanks and rises up and overflows into decant channels. Sediment settles at the bottom. 90 % of sediment is removed at this stage |
| Filtration | Water is passed through large beds of sand, removing any remaining suspended solids. This water is not yet fit for drinking as it may contain harmful bacteria |
| Chlorination | Chlorine is added to sterilise the water. Only 0.5 ppm |
| Fluoridation | Fluoride compounds must be added to the water, by law. 1ppm should be added. This may include compounds such as NaF Sodium Fluoride and Hexafluorosilicic acid H2SiF6. Helps strengthen teeth enamel |
| pH Adjustment | pH of water should be 7.2. If it is too acidic CaOH (lime) is added. If it is too basic H2SO4 or CO2 is added |
| Eutrophication | The enrichment of water with nutrients, leading to excessive growth of algae and other plants |
| Primary Sewage Treatment | Mechanical process in which large solids are removed by screening and some suspended solids are removed by settlement |
| Secondary Sewage Treatment | Biological oxidation process in which levels of suspended and dissolved organic materials are reduced |
| Tertiary Sewage Treatment | Removal of Phosphorous compounds by precipitation and |
| Principle of Colorimetry | Amount of absorbance of light by a coloured solution is proportional to the concentration of the solution |
| Electrolysis | The use of electricity to bring about a chemical reaction in an electrolyte ( Splitting using electricity) |
| Electrolyte | A compound that when molten or dissolved in water, will conduct an electric current |
| Redox in Electrolysis | Oxidation occurs at the positive electrode. Reduction occurs at the negative electrode |
| Electroplating | Using Electrolysis to put a layer of one metal on the surface of another |
| Electrochemical Series | List of elements in order of their standard electrode potential |
| ES list | - K - Ca - Na - Mg - Al - Zn - Fe - Pb - H - Cu - Hg - Ag - Au |
| Organic Chemistry | Study of compounds of Carbon |
| Hydrocarbon | Compounds that only contain Hydrogen and Carbon |
| Fossil Fuels | Fuels formed from the remains of plants and animals millions of years ago |
| Saturated Compound | A compound with only single bonds between atoms in a molecule eg. Alkanes |
| Homologous Series | A series of compounds of similar chemical properties, showing gradations in physical properties, having a general formula for its members, having a similar method of preparation and each member differing from the previous member by a CH2 unit. |
| Structural Isomers | Compounds with the same molecular formula but different structural formulas |
| Unsaturated Compound | Contains one or more double or triple bonds between atoms in a molecule. eg. Alkenes or Alkynes |
| Aliphatic Compounds | Organic compound that consists of open chains of carbon atoms and closed compounds (rings) that resemble them in chemical properties |
| Aromatic Compounds | Compounds that contain benzene ring structure in their compound |
| Refinery Column | Refinery Gas, Petrol, Naphtha, Kerosene, Diesel Oil, Lubricating Oil, Fuel Oil, Bitumen |
| Auto Ignition | Premature Ignition of the petrol- air mixture before normal ignition if the mixture by a spark takes place |
| Octane Number | The measure of the tendency of the fuel to resist knocking (Auto ignition) |
| Examples of Octane Number | 2,2,4-trimethylpentane has an Octane No of 100, Has a low tendency to knock Heptane - 0, Very likely to knock |
| Factors effecting Octane number | Length of Chains- Shorter, higher ON Branching- Less branching, lower ON Structure- Cyclic structure, Higher ON |
| How to increase Octane Number | -Isomerisation -Catalytic Cracking -Dehydrocyclisation -Adding Oxygentates |
| Isomerisation | Changing straight chain alkanes into their isomers |
| Catalytic Cracking | Breaking down long chain HCs via heat and catalysts to make short chain molecules, for which there is a greater demand |
| Dehydrocyclisation | Using catalysts to create ring compounds and removing hydrogen |
| Adding Oxygenates | Adding Oxygen to HCs. eg. MTBE - Methyl Tertiary-Butyl Ether, Ethanol, Methanol. Adding Oxygen creates 'cleaner' fuels |
| Exothermic | Giving out heat |
| Endothermic | Taking in Heat |
| Hydrogen Production | -Steam Reforming - Electrolysis of Water - Haber Process |
| Heat of Reaction | Heat Change when the numbers of moles of the reactant indicated in the balanced equation for the reaction react completely |
| Heat of Combustion | The heat change when exactly one mole of the substance is completely burned in excess oxygen |
| Kilogram Calorific Value | Heat energy produced when 1KG of the fuel is completely burned in oxygen |
| Bond Energy | Average energy required to break one mole of a particular covalent bond and to separate the neutral atoms completely from each other. |
| Heat of Neutralisation | Heat change when one mole of H+ ions from an acid reacts with one mole of OH- ions from a base. |
| Heat of Formation | The heat change that takes place when one mole of a compound in its standard state is formed from its elements in their standard states |
| Hess' Law | If a Chemical reaction takes place in a number of stages, the sum of the heat changes in the separate stages is equal to the heat change if the reaction is carried out in stages. |
| Law of Conservation of Energy | Energy cannot be created or destroyed, but simply moves from one form to another. |
| Chloroalkane | Compound in which one or more of the Hydrogen atoms have been replaced with Chlorine atoms |
| Functional Group | The atom or group of atoms which are responsible for the characteristic properties of an organic compound or a series of organic compounds. |
| Primary Alcohol | Where the carbon atom joined to the -OH group is attached to only one other carbon atom. eg. Ethanol |
| Secondary Alcohol | Where the carbon atom attached to the - OH group is attached to two other carbon atoms. eg. Propan-2-ol |
| Tertiary Alcohol | Where the carbon atom joined to the -OH group is attached to three other carbon atoms. eg. 2-methylpropan-2-ol |
| Alcohols | -OH group |
| Aldehydes | O // -C Group \ H |
| Ketones | O // R - C Group \ R |
| Carboxylic Acids | O O // || -C or -C-OH groups \ OH |
| Condensation Reaction | Chemical Reaction where two molecules combine to form a larger molecule with the loss of a smaller molecule such as water |
| Steam Distillation | Separation process used to isolate compounds at temperatures below their decomposition temperatures. it is carried out by bubbling steam through material and distilling off the immiscible liquids |
| Principle of Steam Distillation | Mixture of 2 immiscible liquids boil at a temperature that is below that of the boiling point of the two. The hot mixture of H2O vapour an oil is passed through a condenser and distillate is collected from the mixture. |
| Emulsion | Dispersion of small droplets of one liquid into another liquid in which it is not soluble. |
| Liquid-Liquid Emulsion | A technique in which two immiscible liquids are separated using a solvent in which one of the components of the mixture has a higher solubility than the other |
| Substitution Reaction | A chemical reaction in which an atom or group of atoms in a molecule is replaced by another atom or group of atoms |
| Mechanism | Detailed step-by-step description of how an overall reaction occurs |
| Chain Reaction | A reaction that continues on and on because a product from one step of the reaction is a reactant for the other step of the reaction. |
| Mechanism of Formation of Chloromethane 1. | - Initiation : splitting Cl2 to two Cl free radicals. UV needed - Propagation: Cl binds to H in methyl group. Leaving HCl and methyl free radical |
| Mechanism of Formation of Chloromethane 2. | - Propagation 2: Free methyl radical attacks a Cl molecule and forms chloromethane, leaving behind a Cl radical -Termination: Reaction comes to an end, resulting in Cl2, CH3Cl (chloromethane) and C2H6 (Ethane). |
| Addition Reaction | Where one or molecules react together to form a single molecule |
| Mechanism of Ethene and Bromine 1. | - Polarisation: C=C bond in ethene is highly negative Br approaches and becomes polarised -Heterolytic Fission: Two different species are formed Br+ ,Br- |
| Mechanism of Ethene and Bromine 2. | - Carbonium Ion Formation: The Br+ in order to gain 2e- needs to give it a stable octet, so attacks C2H4 to make a carbonium atom. -Ionic Addition: Cyclic Carbonium ion is attacked by Br- ion. Ionic addition across the double bonds. |
| Polymers | Long Chain molecules made by joining together many small molecules |
| Repeating Unit | Part of the polymer whose part repeats except for in the end groups. |
| Elimination Reaction | Where one small molecule is removed from a larger molecule to leave a double bond in the larger molecule. |
| Organic Synthesis | The process of making organic compounds from simpler starting molecules |
| Recrystallisation | Process of repeated crystallisation in order to purify or obtain a more satisfactory crystals of a solid that is already pure |
| Chromatography | Separation technique in which the mobile phase carrying a mixture moves in contact with a selectively absorbent stationary phase |
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