AS edexcel chemi definiftions

Symbols

are used to represent elements, eg Fe for iron and C for carbon

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Formulae

are used to represtent compounds, eg H2O for water and NaCl for sodium chloride

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Molecular formula

shows the numbers of atoms of the different elements in one molecule of an compound, eg. CH4 for methane and C2H6 for ethane

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Empirical formula

shows the simplest whole number ratio of the atoms of different elements in a compound. eg CH4 for methane and CH3 for ethane

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balanced chemical equation

desribes a chemical reaction using symbols for the reactants and products. The numbers of each kind of atom are the same on both sides of the equation

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thermal decomposition

is the breaking up of substances into simpler substances by heating

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spectator ions

are ions which take no part in a reaction

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acids

are substances which donate hydrongen ions, H+ (protons)

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bases

are substances which accept hydrogen ions, H+ (protons)

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Alkalis

are soluble bases

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neutralisation

occurs when H+ ions react with OH- or O2- ions forming water

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salts

are the ionic compounds formed when an acid reacts with a base. Most salts are metal/non-metal compounds

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relative molecular mass

is the sum of the relaive atomic masses of all the atoms in its molecular formula

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relative formular mass

is the sume of the relative atomic masses of all the atoms in its formula

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Molar mass

is the mass of one mole of a chemical - the unit is gmol-1. As always with molar amounts , the symbol ot formula of the chemical must be specified

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molar volume

is the volume of 1 mole. At room temperature and atmospheric pressure, the molar volume of all gasses is 24dm3mol-1

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concentration/ gdm-3

= moss of solute/g / volume of solution/dm3

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concentration/ moldm-3

= amount of solute/mol / volume of solution/dm3

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actual yeild

is the mass of the product obtained

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Theoretical yeild

is the mass of the product obtained if the reaction goes according to the equation

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percentage yeild

= (actual yeild / theretical yeild) x100

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limiting reactant

is a substance which is present in an amount which limits the theoretical yeild. Often some reactants are added in excess to ensure that the most valuble reactant is converted to as much product as possible.

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Atom economy

= (mass of atoms in desired product / mass of atoms in all reactants) x100

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enthalpy change

is the overall energy exchanged with the surroundings when a change happens at constant pressure and the final tempurature is the same as the starting temperature

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specific heat capacity, c

is the energy needed to raise the temperature of 1g of material by 1K for water c = 4.2Jg-1K-1

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the standard enthalpy change of reaction

is the energy transferred when the molar quantities of reactant as started in the equation react under standard conditions

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the standard enthalpy change of neutralisation

is the enthalpy change when the amounts of acid and alkali in the equation for the reaction neutralise each other under standard conditions

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the standard enthalpy change of combustion

is the enthalpy change when one mole of the substance burns completely in oxygen under standard conditions

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the standard enthalpy of formation

is the enthalpy change when one mole of the compound forms from its elements under standard conditions with the elements and the compound in their standard states

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the standard enthalpy change of atomisation

id the enthalpy change when one mole of gaseos atoms is formed from the element under standard conditions

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Hess's Law

says that the enthalpy change in converting reactants to products is the same regardless of the route taken, provided the initial and final conditions are the same

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bond enthalpy

of a particular bond is the energy required to break one mole of the bonds in a substance in the gaseous state

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atomic number

of an atom is the number of protons in its nucleus. (Atomic number)

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mass number

of an atom is the number of protons plus neutrons in its nucleus. (nucleon number)

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Isotopes

atoms of the same element with the same atomic number, but different mass number

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relative isotopic mass

is the mass of one atom of an isotope relative to the mass of one atomfir of carbon-12, for which the relative mass is definied as exactly 12

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first ionisation energy

is the energy needed to remove one electron from each atom in one mole of gaseous atoms

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an orbital

is a region of space around the nucleus of an atom in which there is a 95% chance of finding an electron, or pair of electrons with opposite spins

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electron configuration

decribes the number and arrangement of electrons in an atom.

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lattice

to describe a regular arrangement of atoms or ions in a crystal

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Delocalised electrons

are bonding electrons which are not fixed between two atoms in a bond. They are free to move and are shared by several or many atoms

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metalic bonding

is the strong attraction between a lattic of positive metal ions and a 'sea' of delocalised electrons.

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electrolysis

is the decomposition of a compound by eletricity- the compound is usually decomposed into it constituent elements. The compound which is decomposed is called an electrolyte and we say that it has been electrolysed

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the first electron affinity

is the energy chane when each atom in one mole of gaseous atoms gain one electron to form one mole of gaseous ions with a single negative charge

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lattice energy

is the standard enthalpy change when one mole of the compound forma from free gaseous ions

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polarisation

is the distortion of the electron cloud in a molecule or ion by nearby charge

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Dative covalent bond

is a bond in which two atoms share a pair of electrons, both the electrons being donated by one atom

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functional group

is the group of atoms which gives an organic compound its characteristc properties and reactions

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structual formula

shows in minimal detail which atoms, or groups of atoms, are attached to each other in one molecule of a compound

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displayed formula

shows all the atoms and all the bonds between them in one molecule of a compound

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skeletal formular

shows the functional group fully, but the hydrocarbon part of a molecule, simply as lines between carbon atoms and hydrogen atoms

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structural isomers

are compounds with the same molecular formula but different structural formulae

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free radicals

highly charged single atoms, or groups of atoms, with unpaired electrons

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nucleophiles

are ions or molecules with a lone pair of electrons that attack positive ions or positive centres

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electrophiles

are reactive ions and molecules which attack negative ions or negative centres in molecules

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aliphatic hydrocarbons

are straight-chain and branched hydrocarbonswith no rings of carbon atoms

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alicyclic hydrocarbon

are hydrocarbons with at least one ring of carbon atoms

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arenes

are hydrocarbons with a ring or rings of carbon atoms in which there are delocalised electrons

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substitution reaction

is one in which an atom, or group of atoms is replaced (substituted) by another atom, or group of atoms.

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intiation

the step which produces free radicals

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propagation

steps which form products and more free radicals

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termination

steps which remove free radicals by turning them into molecules

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sustainable lifestyle

involves living within the means of the environment in order that the Earth's natural resources are available for future generations

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unsaturated

compounds contain one or more double or triple bonds between atoms in their molecules. The term is often applied to alkenes and to describe unsaturated fats which have C=C double bonds in the hydrocarbon chains

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cis and trans isomers

are molecule with same molecular formula, the same structural formula, but different displayed formulae

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addition reaction

is a reaction in which two molecules add together to form a single product

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Intermediates

are atoms, molecules ions or free-radicals which do not appear in the overall equation for a reaction, but which are formed during one step of a reaction and then used up in the next

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Addition polymerisation

is an addition reaction in which small molecules, called monomers, join together forming a giant molecule, called a polymer.

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bond angle

is the angle between two covalent bonds in a molecule or giant covalent structure

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bond angle

is the distance between the nuclei of two atoms linked by one or more covalent bonds. For the same two atoms, triple bonds which, in turn are shorter than double bonds which, in turn, are shorter than single bonds.

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Allotropes

are different forms of the same element in the same physical state

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composities

combine two or more materials to create a new material which has the more desirable properties of both it consituents.

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polar covalent bonds

are bonds between atoms of different elements. The shared electrons. The bonds have a positive pole at one end and a negative pole at the other.

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elctronegavitivity

is a measure of the pull of an atom of an element on the shared electrons in a covalent bond. In a polar bond the shared electrons are draw towards the more electronegative atom.

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polar molecules

have polar bonds which do not cancel each other out, so that the whole molcule is polar

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Intermolecular forces

are weak attractive forces between moloecules

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London forces

are the intermolecular forces between all molecules. The arise from the attraction between temporary dipoles they induce in neighbouring molecules

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Polarisability

is an indication of the extent to which the electron cloud in a molecule can be distorted by a nearby electric charge

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hydrogen bonding

is a type of attraction between molecules which is much stronger than other types of intermolecular force, but much weaker than covalent bonding

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a solute

is a chemical which dissolves in a sovlent to make a solution

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saturated solution

ccontains as much of the solute as possible at a particular temperature

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solubility

is a measure of the concentration of a saturated solution of a solute at a specified tempurature

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non-aqueous solvent

is any solvent other than water

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miscrible

are liquids that mix with each other

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hydration

takes place when water molecules bond to ions or add to molecules. Water molecules are polar so they are attracted to both positive ions and negative ions

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ionic equation

decribes the chemical changes by showing only the reacting ions, leaving out spectator ions

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half-equation

is an ionic equation used to describe either the gain or the loss of electrons during a redox reaction

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oxidation

the gain of oxygen, loss of electrons or the loss of hydrogen

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reduction

the loss of oxygen, gain of electrons or the addition of hydrogen

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basic oxidation

is a metal oxide which reacts with acids to form salts and water. The oxide ions acts as a base and accepts the hydrogen from the acid. Oxides which disolve in water are alkalis

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disproportionation

is a change in which the same element both increases and decreases its oxidation number. So the element is both oxidised and reduced

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a standard solution

is a solution with an acurately know concentration.

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primary standard

is a chemical which can be weighed out accurately to make up a standard solution

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end-point

is the point during a titration when enough of the solution in the burette has been added to react exactl with the amount of chemical in the flask

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precise results

are mesurements that when repeated have a small random error

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bias

arises from systematic errors which can affect all the measurements in the same way, making them all higher or lower than the true value. They do not average out

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accurate results

are precise and free from bias

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chemical kinetics

is the study of the rates of chemical reactions

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reaction profile

is a graph which shows how the total enthalpy (energy) of the atoms, molecules or ions changes during the process of a reaction from reactants to products

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activation energy

is the height of the energy barrier separating reactants and products during a chemical reaction. It is the minimum energy needed for a reaction between the amounts, in moles, shown in the equation for the reaction

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primary

the functional group is at the end of the chain

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secondary

the functional group is somewhere along the chain

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tertiary

the functional group is on a branch on the chain

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reflux condenser

is fitted to a flask to prevent vapour escaping while a liquid is beatin heated

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hydrolysis

is a reaction in which a compound splits in a reaction involving water

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the mass to charge ratio

is the ratio of the relative mass of an ion to its charge, where e is the number of charges.

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absorption spectum

is a plot showing how strongly a chemical absorbs radiation over a range of frequecies

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wavenumber

is the number of waves in 1cm

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transmittance

measures the percentage of radiation which passes through the sample. The troughs appear at those wavenumbers where the compound absorbs strongly

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green chemistry

is the design of chemical processes and products that reduce or eliminate the production and use of hazardous chemicals

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sustainalble development

meets the needs of the presents without compramising the ability of future generations to meet their own needs

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anthropogenic effects

are the changes brought about by human activities. they include factors that affect the atmophere, such as burning fossil fules, deforesation and intensive agriculture

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carbon footprint

measures the total amount of greenhouse gasses produced by a process or product in tonnes of carbon dioxide

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coarbon dioxide equivilent, CO2 eq.

is the measure of in terms of the quantity of carbon dioxide that would have the same global warming effect

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carbon neutal

is a process where the CO2 released is balances by actions which remove an equivalent amount of CO2 from the atmosphere

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AS edexcel chemi definiftions

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