Higher: Chemistry
Complete revision cards for the SQA Higher Chemistry Course
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Higher: Chemistry - Marcador
Higher: Chemistry - Detalles
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| What is periodicity? | The occurrence of patterns in the periodic table |
| What is a group in the periodic table | A vertical column containing element with similar chemical properties and the same number electrons in the outer shell |
| What is a period in the periodic table? | Rows of elements arranged with increasing atomic numbe |
| What is covalent radius | Half the distance between the nuclei of two bonded atoms of the element; gives a measure of the size of an atom |
| What is the trend in covalent radius across period | Decreases number of protons in nucleus increases across a period higher nuclear charge higher electrostatic attraction between electrons and nucleus atom becomes smaller |
| What is the trend in covalent radius down a group | Increases no. of occupied energy levels increases down a group less electrostatic attraction between electrons and nucleus atom size increases |
| What is first ionisation energy | The first ionisation energy is the energy required to remove one electron from each atom of one mole of gaseous atoms. |
| What can first ionisation energy of any element be represented by in a chemical equation | M(g) → M+(g) + e- |
| What is second ionisation energy | Energy required to remove one electron from each singly positive ion of one mole of the gaseous ions. |
| How can the second ionisation energy of any element be represented in a chemical equation | M+(g) → M2+(g) + e- |
| Why are ionisation energies endothermic? | Energy is required to remove an electron from any atom because there is an attractive force between the nucleus and the electron being removed which has to be overcome. |
| What is the trend in ionisation energy across a period | Increases no. of protons in nucleus increases across a period increased nuclear charge greater electrostatic attraction between nucleus and electrons more energy required to remove electrons |
| What is the trend in ionisation energy down a group | Decreases number of energy levels increases going down a group electron being removed is further from the nucleus electron is more shielded from nucleus by inner energy lefvels weaker electrostatic attraction between electrons and nucleus less energy required to remove electron |
| Why are second and third ionisation energies larger than the first | The extra positive nuclear charge has greater electrostatic attraction for the outer electrons and therefore more energy is required to remove subsequent electrons. |
| Why is the second ionisation energy of alkali metals much higher than the first | The second ionisation energy is much higher than would be expected because this electron is being removed from a full outer energy level which is: a very stable arrangement closer to the nucleus less screened from the nucleus as there are fewer inner electron energy levels. |
| What is electronegativity | Electronegativity is a measure of the attraction an atom involved in a bond has for the electrons of the bond. |
| What is the trend in electronegativity across a period? | Increases the nuclear charge increases nucleus has a stronger electrostatic attraction for electrons |
| What is the trend in electronegativity down a group? | Electronegativity decreases atomic size increases due to the increase in the number of occupied energy levels electrons are further from the nucleus nucleus is more screened by inner occupied energy levels electrostatic attraction between the nucleus and electrons is reduced |
| How are industrial processes designed? | To maximise profit and minimise impact on the environment |
| What factors can influence industrial process design | Availability, sustainability and cost of feedstock opportunities for recycling energy requirements marketability of by products product yield |
| What environmental factors are taken into consideration when designing industrial processes | Minimising waste avoiding the use or production of toxic substances designing products which will be biodegradable if appropriate |
| What is meant by a raw material | Natural resources that can be obtained from the earth that have not undergone any chemical processing |
| Give examples of raw materials | Fossil fuels metallic ores minerals air water salt |
| What is a feedstock | Reactive components extracted from raw materials by a chemical process. other chemicals can be extracted or synthesised from feedstocks |
| Give examples of feedstocks | Ethene benzene |
| What is a consumer product | Product manufactured for use in society (which usually has a major impact on quality of life) |
| Give examples of consumer products | Detergents fertilisers cosmetics toiletries |
| What else could be produced in the manufacture of a consumer product (apart from the consumer product itself) | An unwanted side product |
| How can taking into account availability, sustainability and cost of raw materials or feedstocks make profit in industry? | When raw materials/feedstocks are available locally, transport costs are reduced, it is more environmentally friendly |
| How can taking into account availability, sustainability and cost of raw materials or feedstocks cause loss of profit in industry? | Some supply is expensive, not readily available or unpredictable, so alternatives will need to be found |
| How can finding opportunities for recycling make profit in industry? | Unreacted chemicals can be easily fed back into the reactor, making the process more economical |
| How can finding opportunities for recycling cause profit loss in industry? | Unreacted chemicals are difficult to separate from the end product, which makes the process inefficient |
| How can energy requirements make profit in industry? | Exothermic reactions can sustain reaction temperature as heat can be conserved or recycled use of catalyst allows reactions to be carried out at a lower temperature |
| How can energy requirements cause profit loss in industry? | Endothermic reactions can be costly as energy (gas, electricity) has to be purchased) providing a cool temperature can also be costly due to the cost of refrigeration or coolant |
| How can use of by product make profit in industry | In some cases, by products can be used in the process or sold for profit |
| How can use of by product cause profit loss in industry | Some by products are toxic, corrosive or environmentally damaging this can be costly to deal with |
| How can product yield make profit in industry | If product yield is high then this process is profitable |
| What is the formula for calculating number of moles when given mass and gfm | N=m/gfm n is number of moles in mol m is mass in g gfm is gram formula mass in g |
| What is the formula for calculating the number of moles when given concentration and volume | N=cV n is number of moles in mol c is concentration in mol l-1 V is volume in l |
| What is the formula for molar volume | Vmol=V/n Vmol is molar volume in l mol-1 V is volume in l n is number of moles in mol |
| What is percentage yield used for | Used to compare the yield of a product actually obtained with what could have been obtained in theory (if all of the reactants were converted with no waste) |
| What is atom economy used for | A measure of the percentage of reactant that become useful products used more in industry than percentage yield as it tells chemists how efficient a process actually is |
| What is meant by an unsaturated hydrocarbon | Compounds containing at least one carbon to carbon double bond |
| What is a saturated compound | Compounds containing only single carbon to carbon bonds |
| What is an addition reaction | When two molecules combine to form a single molecule |
| What is hydrogenation | Reaction between an alkene and hydrogen to form an alkane |
| What is hydration | Reaction between an alkene and water to form an alcohol |
| How are dihaloalkanes formed | When alkenes react with halogens |
| What kind of compounds can undergo addition reactions | Unsaturated compounds (those containing carbon to carbon double bonds) |
| How do you test for unsaturation | An unsaturated compound will quickly decolourise bromine solution |
| What is a full structural formula | Shows all the bonds present in a compound |
| What is a shortened structural formula | Shows the order of the atoms but omits the carbon to hydrogen bonds eg. CH3CH2CH2CH3 |
| What is an isomer | Compounds with the same molecular formula but different structural formula |
| What are two features of isomers: | May belong to different homologous series usually have different physical properties |
| What is the effect of hydrogen bonding on solubility | The presence of O-H or N-H bonds will increase the solubility of a compound this is due to the covalent bond formed between hydrogen and the highly electronegative O, N or F elements. Hydrogen bonding indicates the molecules are polar and hence soluble in water. |
| What type of solvents can dissolve molecules with permanent dipole interactions | Polar solvents Molecules with permanent dipole are considered polar so therefore tend to be soluble in polar solvents. |
| What happens to boiling point as you increase the size of a compound | Increases when molecule size increases number of electrons increases therefore higher chance of instantaneous dipoles and higher LDF's as a result. |
| What is volatility | A measure of the ease of evaporation of a substance |
| What happens to volatility as you increase the size of a molecule | Volatility decreases as when molecule size increases, there are more electrons, more chance of instantaneous dipoles and stronger LDF's, meaning more energy is required for the substance to boil and therefore evaporate |
| What happens to the melting point of metals down a group | Melting point decreases as there are more occupied energy levels, and so the nucleus is further away from delocalised electrons. The inner energy levels also screen the nucleus from delocalised electrons, decreasing the strength of the metallic bond |
| What is the name given to bonding inside molecules | Intramolecular bonds |
| What is a metallic bond | The electrostatic force of attraction between positively charged ions and delocalised electrons |
| What is the metallic structure | A giant lattice of positively charged ions in a sea of delocalised electrons |
| Name some properties of metals | Electrical conductors due to delocalised electrons high melting points due to having to break the strong metallic bonds malleable and ductile as the metallic bond acts in all directions good thermal conductors as the atoms are closely packed and can pass on heat through conduction |
| What happens to metal electrical conductivity across a period | It increases as there are more delocalised electrons |
| What happens to metal melting point across a period | Melting point increases as the positive core is increasing in charge and the number of delocalised electrons increases, creating a stronger metallic bond |
| What happens to the melting point of metals down a group | Melting point decreases as there are more occupied energy levels, and so the nucleus is further away from delocalised electrons. The inner energy levels also screen the nucleus from delocalised electrons, decreasing the strength of the metallic bond |
| What is the name given to bonding between molecules | Intermolecular bonding |
| What are the three types of intramolecular bonds | Non polar covalent bonds polar covalent bonds ionic bonds |
| When do non polar covalent bonds occur | Non polar covalent bonds exist between two atoms with the same electronegativities. Electrons are shared equally. Pure covalent bonds have no ionic character. |
| What is a polar covalent bond | Polar covalent bonds are formed in compounds when atoms of different elements share electrons. Atoms with different electronegativity values will share the bonding electrons unequally, forming a permanent dipole. |
| What is a dipole | When an atom is slightly positive (?+) or slightly negative (?-) due to unequal sharing of electrons. |
| How are ionic bonds usually formed? | Between a metal and non-metal with a large difference in electronegativity |
| Describe why sodium chloride is an ionic compound | Chlorine has far larger electronegativity chlorine pulls bonding electrons towards itself completely chlorine gains electron and forms negative ion sodium loses its bonding electron and forms a positive ion |
| How is ionic formula written | By giving the simplest ratio of each type of ion in the substance eg. sodium chloride forms an ionic lattice and the ratio of sodium to chlorine is 1:1, which is why its formula is NaCl |
| What determines the type of bonding present in a compound | The differences in electronegativity between the elements involved |
| If two ions have a very large difference in electronegativity, what does that mean about the ionic character of the compound? | The compound is very ionic |
| Name properties of ionic compounds | Ionic compounds are high melting point solids due to the strong electrostatic attraction between oppositely charged ions that have to be overcome on melting do not conduct electricity when solid as the ions are not free to move conduct electricity when molten or in solution as the ions are free to move many ionic compounds are soluble in water |
| What are the properties of covalent network substances | Very high melting points as strong covalent bonds have to be broken on melting form very hard substances are the atoms are held together in a giant network do not conduct electricity as there are no free charged particles are insoluble in water |
| What are the two types of van der waals forces | London dispersion forces of attraction permanent dipole permanent dipole forces of attraction |
| What is the strength of london dispersion forces relative to other intermolecular bonds | They are the weakest intermolecular bonds, they exist between all atoms and molecules |
| How do we know that london dispersion forces exist between molecular elements and monatomic elements | They will condense, fomring solids if cooled to sufficiently low temperatures, which means there must be an attraction between the individual molecules that is being overcome |
| How are london dispersion forces caused | Due to uneven distribution of electrons within an atom slightly negative and slightly positive side of an atom; instantaneous dipole instantaneous dipole induces instantaneous dipoles in neighbouring atoms |
| What is the strength of london dispersion forces dependent on | The size of the molecule or atom larger atoms and molecules have more electrons, leading to larger dipoles being established |
| When do permanent dipole permanent dipole forces occur | They occur between polar molecules atoms in polar molecules have different electronegativity & electron pair is shared unequally one atom is slightly positive and the other slightly neagative oppositely charged ends of molecule are attracted to each other |
| What is hydrogen bonding | A specific type of permanent dipole permanent dipole attraction occurs when hydrogen atom is covalently bonded to nitrogen oxygen or fluorine |
| Why mightn't a substance that contains polar covalent bonds be overall polar? | The shape of the molecule water is a polar molecule but due to the non symmetrical shape of the molecule (angular) the molecule itself is polar, due it it having a slightly positive and slightly negative side carbon tetrachloride has four polar covalent bonds, it is a tetrahedral molecule so the charges are symmetrical. The molecule itself is non polar due to symmetry. |
| What are the properties of covalent molecular substances | They have low melting and boiling points they do not conduct electricity some covalent molecular compounds have higher melting points than expected, this is often due to hydrogen bonding |
| Why does water have some unusual properties | Due to the hydrogen bonding between its molecules |
| Name some unusual properties of water | The density of ice is less than water, due to the water expanding as it is frozen, because of the hydrogen forming an open type lattice high surface tension relatively high viscosity |
| Describe the solubility of all ionic lattices and polar covalent molecules (like dissolves like) | Soluble in water and other polar solvents insoluble in non-polar solutions |
| Describe the solubility of all non-polar covalent substances (like dissolves like) | Soluble in non-polar solvents insoluble in water and other polar solvents |
| What is oxidation? | The loss of electrons by a reactant in any reaction |
| What is reduction? | The gain of the electrons by a reactant in any reaction |
| What are the steps in writing balanced ion-electron equations for reactions not found in your data booklet? | Balance oxygen atoms with water molecules balance hydrogen atoms with hydrogen ions balance the charges with electrons |
| Write out the balanced ion electron equation for MnO4- (aq) → Mn2+ (aq) | Balance any oxygen atoms with water molecules MnO4- (aq) → Mn2+ (aq) + 4H2O (l) Balance any H atoms with H+(aq) ions MnO4- (aq) + 8H+ (aq) → Mn2+ (aq) + 4H2O (l) Balance the charges with electrons MnO4- (aq) + 8H+ (aq) + 5e- → Mn2+ (aq) + 4H2O (l) |
| How can you tell if a reaction is a redox reaction? | Reaction involves metal atoms as a reactant or a product reaction involves molecules and ions of the same non-metal reaction involves a metal ion with two different charges sulfate reacting to form sulfite and vice versa |