Flashcards

Additional Science-Chemistry

bneale English 37 cards

Cards in this deck (37)

1Electron shells -The electrons in an atom are arranged in electron shells, or energy levels around the nucleus.Electronic configurations
-The electrons fill the shells that are closest to the nucleus first.
2Atoms and ions -An atom has the same number of protons and electrons. It had no overall charge, because the positive charges on the protons are balanced by the negative charges of the electrons -An atom can become an ion by gaining or losing one or more electrons. An ion has a charge because it no longer has the same number of protons and electrons.We show that the atom has become an ion by adding a + or - sign to the symbol.
3Cations Metal atoms lose electrons to form positively charged cations. -Metals in group 1 lose 1 electron to form ions with a 1+ charge. -Metals in group 2 lose 2 electrons to form ions with a 2+ charge.
4Anions Non-metal atoms (or groups of atoms) gain electrons to form negatively charged anions. -Elements in group 6 gain 2 electrons to from ions with a 2- charge. -Elements in group 7 gain 1 electron to from ions with a 1- charge
5Precipitates -If you mix solutions of two soluble salts, the ions in the mixture can combine to form new salts. If one of the new combinations produces an insoluble salt, it will appear as a precipitate. You can use the solubility rules to work out if a precipitate will form.Preparing salts
-Pure samples of insoluble salts can be prepared using precipitation reactions.
-Mix solutions of two substances that will form the insoluble salts.
-Filter the mixture. The insoluble salt will be trapped in the filter paper
-Wash the salt with pure water.
-Leave the salt to dry on the filter paper. It could be dried in an oven.
6Ion tests Flame tests -Some metal ions can be identified using flame tests. A damp splint is placed in the solid and then held in the Bunsen burner flame. The colour flame identifies the ions.Sodium (NA+)=Yelow
Potassium (K+)=Lilac
Calcium (CA2+)Red
Copper (CU2+)=Green-blue
7Chloride ions (CL-) Test: Add a few drops of dilute nitric acid to the solution -Shake the mixture -Add a few drops of silver nitrate solution. If the substance contains chloride ions: -a white precipitate of silver chloride forms.
8Simple molecular substances -There are only weak forces between the molecules. These substances have low melting point and boiling points. These substances are liquids or gases at room temperature, or solids with low melting points, such as sugar, wax or iodine. -There are no charged particles, so simple molecular covalent substances do not conduct electricity.
9Giant molecular covalent substances --The covalent bonds in a giant molecular substances are strong. It takes a lot of energy to break these bonds so melting point are very high. These substances are very hard and do not conduct electricity.-Diamond is a giant molecular covalent substance and is made of billion of atoms all joined.
-Graphite is also a giant molecular covalent substance, so it has high melting point, but some of it's properties are different to diamond. It does not conduct electricity, and is very soft.
10-Diamond is used for cutting tools because it is very hard -Graphite is used as a lubricant because the forces between the layers are weak and the layers can slide over each other easily. -In graphite, there is one electron form each carbon atom that can move along the layers, so graphite conducts electricity and can be used to make electrodes.
11Miscible or immiscible -Miscible liquids mix completely with each other. -Immiscible liquids do not mix completely.Separating miscible liquids
Miscible liquids can be separated using fractional distillation.
-The mixture is heated, and the vapours pass into a fractionating column.
-As the gases cool down, the ones with the highest boiling points condense first.
-Different liquids are collected at different places in the column
12Distillation of liquid air -Nitrogen and Oxygen are obtained from air by fractional distillation. The air had to be turned to a liquid first by cooling it. --The top of the column is colder. At -190C, the nitrogen is still a gas but any oxygen reaching this part of the tower is likely to condense and fall to the bottom --185C is above the boiling point of nitrogen and so the nitrogen boils and evaporates. --185C is below the boiling point of Oxygen and a lot of the oxygen stays as a liquid (although some evaporates) --200C is below the boiling points of both nitrogen and oxygen so they are both liquids. $Distillation of liquid air -Nitrogen and Oxygen are obtained from air by fractional distillation. The air had to be turned to a liquid fi...$
13Chromatography Most inks, paints, dyes and food colourings are mixtures of different coloured compounds. Chromatography can be used to separate the different substances in these mixtures.-
14Paper chromatography -lid to stop evaporation of solvent -Solvent front to show the solvent has reached that level. -The different compounds in a sample dissolve to different extents in thee solvent. -More soluble compounds are carried up the paper faster than less soluble ones, so the compounds separate out. -Drops of the different samples are put onto paper and allowed to dry.The bottom of the paper is then dipped into a solvent. -Solvent(this can be water or some other liquid that the samples will dissolve in.
15Rf values -The Rf value of a compound is always the same as long as the chromatograhy is carried out in the same way, under the same conditions. Rf values can be used to identify compounds from a chromatogram.Rf=distance moved by compound
-------------------------------------------
distance moved by solvent
16Chromatography can be used... - in the food industry, to check which colourings are used in food in forensic science, to analyse DNA samples or paints and inks from crime scenes.
17Metals and bonding -metals are malleable and can conduct electricity.Metallic bonding
-A metal consists of a regular arrangement of positive ions surrounded by a 'sea' of delocalised electrons. These electrons come from the outer shells of the atom an can move around throughout the metal
18Transition metals Transition metals are the metals in the central block of the periodic table. Most metals are transition metals. Transition metals typically: -have high melting points -form coloured compound.
19Alkali metals The alkali metals are in group 1 of the periodic table. The periodic metals: -are soft metals (you can cut them with a knife) -have comparatively low melting points (the are easy to melt)
20Reactions with water -They all have one electron in the outer shell, so when they react, each atom loses one electron to become an ion with a +1 charge.All alkali metals react with water to form a metal hydroxide and hydrogen gas. Metal hydroxide solutions are alkaline.
lithium + water -> lithium hydroxide + hydrogen
2Li(s) + 2H20->2liOH(aq)+ H2(g)
21Reactivity The reactivity of the alkali metals increases down the group. When they are put in water: -lithium floats on the surface and fizzes -sodium melts from the heat produced by the reaction and whizzes around on the surface as a molten ball, and sometimes the hydrogen produced catches fire. -potassium reacts even faster, and the hydrogen produced burns with a lilac flame.-
22Halogens -group 7 -if they gain one electron they will have a full outer shell -all react with metals to form a compound called halides. -Fluorine is the most reactive -reactivity decreases as you go down the group.
23Properties of halogens fluorine-F-Gas at RT-Pale yellow chlorine-Cl-Gas at RT-yellow-green bromine-Br-liquid at RT-red-brown -iodine-i-solid-grey
24Reactions with hydrogen -Halogens react with hydrogen to form hydrogen halides. Hydrogen halides dissolve in water to form acidic solutions. For example, when hydrogen chloride is dissolved in water it forms hydrochloric acid.hydrogen+chlorine->hydrogen chloride
H2(g)+Cl(g)->2HCL(g)
25Noble gases -Group 0 -Full outer shell -'inert' meaning they are difficult to make the react.Welding:
-argon and helium
-the gases are inert so they do not react with the hot metal, and they stop oxygen coming into contact with it.
inside filament light bulbs:
-xenon or argon
-the gases are inert so they do not react with the hot filament
balloons and airships:
-helium
-helium has a lower density and makes the balloons float.
fire-extinguishing systems:
-argon
-argon is non-flammable, so it can be used to put out fires.
26Discovery 1)Lord Rayleigh noticed that the density of nitrogen made in a reaction was lower than the density of nitrogen obtained from air. 2)Sir William Ramsey hypothesised that the air might also contain a denser gas that was mixed with the nitrogen 3)During the experiments Ramsey discovered helium.Later, he also discovered neon, krypton and xenonNoble Gases
27Temperature changes Most reactions involve a T change -In exothermic reactions, heat energy is given out (the reaction mixture or the surroundings become hot) -In endothermic reactions, heat energy is taken in (the reaction mixture gets cold)
28Bonds and energy -When a chemical reaction happens, the bonds that hold the atoms tgether in the molecules of the reactants are broken. The atoms then come together in new arrangements to form the products.-Breaking bonds is endothermic (energy is needed)
-Making bonds is exothermic (energy is released)
29Rates of reaction -Reactions happen when particles of different substances collide with each other. The particles need to collide with enough energy to make the reaction happen, so not all collisions results in a reaction. The higher the frequency of the collisions, and the higher the energy of the collisions, the faster the rate of reaction.REACTIONS
30Changing the rate of a reactions Temperature: Reactions happen faster when the temperature is higher. Particles move faster at higher temperatures, so they collide more often and they also collide with more energy Surface are:Reactions happen faster when solid reactants are broken up into smaller pieces. Smaller pieces have a bigger surface area than the same mass of larger pieces, so there is more opportunity for collisions between reactants.Concentration:Reactions happen faster when more concentrated solutions are used. A more concentrated solution has more solute particles in a given volume. the more particles there are, the more likely they are to collide and react.
Catalyst: A catalyst speeds up a reaction without being used itself.
31Catalytic Converters -Catalytic converters are used in cars to reduce the pollution caused by waste gases from the engine. Carbon monoxide and unburned fuel in the exhaust combine with oxygen to form carbon dioxide and water. The platinum catalyst in catalytic converters is made into a fine mesh to give it a large surface area. This allows more of the waste gases to come into contact with the catalyst and so helps too speed up the reaction. Catalytic converters work best at high temperatures.;
32Relative masses and formulae Relative formula mass is the sum of the relative atomic masses of all the atoms or ions in its formula.Empirical formulae and molecular formulae
-The empirical formula of sodium chloride is NaCL. This means that for every ion of sodium in an ionic lattice there is one chloride ion. For simple molecular compounds, the molecular formula is the actual number of atoms of each element in the molecular.. For example, the molecular formula of water is H20.
33Finding the empirical formula -If you know the mass of the magnesium heated in a crucible and the mass of the magnesium oxide formed then you can work out the mass of oxygen that has combined with the magnesium. From that you can work out the empirical formula.
34Percentage composition -The percentage composition by mass of a compound is a way working out how much an element is present in a compound.Percentage by mass of element in a compound = number of atoms of element X relative atomic mass
--------------------------------
relative formula mass
X100
35Masses of reactants and products -No atoms are created or destroyed in a reaction, so the total mass of the products must be equal to the total mass of the reactants. If you know the mass for one of the reactants or products in a reaction, you can use the balanced equation to work out the masses of the other substances involved.Names of reactants and products
36Yields -The yield of a reaction is the amount of useful product you get at the end.Actual and theoretical yields
-You can calculate the mass of product you expect to get from a reaction using the balanced equation and the relative masses of the compounds. This is the theoretical yield of a reaction.
-Reaction do not always produce the amount of product predicted from the equation. The amount actually produced is called the actual yield.
37Waste and profit -Most reactions have more than one product. Most reactions in the chemical industry produce substances other than the substance being manufactured. These are by-products.Disposing of waste products
-House prices could drop if there is a new chemical plant built, or if there are unpleasant smells.
-We are running out of landfill sites
-Some waste products are harmful, and treating them costs money.
-The smoke from incinerators is not as harmful as the substances that have been burned, but incineration waste can still cause air pollution.
-Lorries taking waste to landfill site cause dust and disturbance.
-Many waste products that are not harmful still need to be disposed of.
-People do not like living near landfill sites.
-Some waste product may accidently scape and cause pollution.