Chemistry definitions

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  • Created by: Bethany62
  • Created on: 18-04-15 10:45
Isotope
atoms of the same element with different numbers of neutrons
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Atomic Number
The number of protons in the nucleus of an atom
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Mass number
The number of particles(protons and neutrons) in the nucleus
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Ion
a positively or negatively charged atom or (covalently bonded) group of atoms(a molecular ion)
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Relative Isotopic mass
The mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12
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Relative atomic mass
the weighted mean mass of an atom of an element compared with one-twelfth the mass of an atom of carbon-12
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Relative molecular mass
The weighted mean mass of a molecule compared with the mass of an atom of carbon-12
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Relative formula mass
the weighted mean mass of a formula unit compared with one-twelfth the mass of an atom of carbon-12
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Avogadro constant
the number of atoms per mole of the carbon-12 isotope (6.02 x 10^23 mol^-1)
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Mole
the amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope
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Molar Mass
The mass per mole or a substance (grams per mole)
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The empirical formula
The simplest whole number ratio of atoms of each element present in a compound
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Molecule
small group of atoms help together by covalent bonds
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Molecular Formula
The actual number of atoms of each element in a molecule
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Molar Volume
the volume per mole of a gas. (dm^3 per mole) at RTP this is 24.0 dm3mol-1.
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Concentration
the amount of solute dissolved in moles per dm^3 of solution
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Standard Solution
A solution of known concentration
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Species
any type of particle that takes place in a chemical reaction
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Stoichiometry
The molar relationship between relative quantities of substances taking part in a reaction
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Acid
A species that is a proton donor
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Base
A species that is a proton acceptor
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Alkali
A type of base that dissolves in water to form hydroxide ions (OH-)
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Salt
A chemical compound formed from an acid when a H+ ion is replaced by a metal cation or other positive ion(NH4+)
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Cation
A positively charged ion
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Anion
A negatively charged ion
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Hydrated
A crystalline compound containing water
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Anhydrous
A substance that contains no water molecules
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Water of crystillisation
water molecules that form an essential part of the crystalline structure of a compound
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Oxidation Number
A measure of the number of electrons that an atom uses to bond with atoms of another element. Oxidation numbers are derived from a set of rules.
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Oxidation
Loss of electrons or an increased oxidation number
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Reduction
Gain of electrons, or a reduced oxidation number
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Redox reaction
a reaction in which both oxidation and reduction take place
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A reducing agent
A reagent that reduces(adds electrons to) another species
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An oxidising agent
A reagent which oxidises(removes electrons from) a species
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First ionisation energy
The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous +1 ions
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Electron shielding
The repulsion between electrons in different inner shells. Shielding reduced the net attractive force of the nucleus on the outer-shell electrons.
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Successive ionisation energies
A measure of the energy required to remove each electron in turn (ie Second ionisation energy = the energy required to remove one electron from each atom of a mole of gaseous +1 ions to form one mole of gaseous +2 ions)
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Shell
A group of atomic orbitals with the same principal quantum number, n, also known as a main energy level
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Principal quantum number (n)
A number representing the relative overall energy of each orbital, which increases with distance from the nucleus. The sets of orbitals with the same n values are referred to as shells or energy levels.
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Atomic orbital
A region within an atom which can hold up to two electrons with opposite spins
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Sub-shell
A group of the same type of atomic orbitals(s, p, d, f) within a shell
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Electron configuration
The arrangement of electrons in an atom
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Compound
A substance formed from two or more chemically bonded elements in a fixed ratio, usually shown by a chemical formula
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Ionic bond
The electrostatic attraction between oppositely charged ions
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Giant Ionic Lattice
Three dimensional structure of oppositely charged ions, held together by strong ionic bonds
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Group
A vertical column in the periodic table (same number of outer-shell electrons and similar properties)
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Covalent Bond
A shared pair of electrons
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Lone pair
An outer-shell pair of electrons which are not involved in chemical bonding
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Dative covalent bond
A shared pair of electrons which has been provided by one of the bonding atoms only
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Electronegativity
The measure of attraction of a bonded element for the pair of electrons in a covalent bond
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Permanent dipole
A small charge difference across a bond that results from a different in electronegtivity of the bonded atoms
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Polar covalent bond
Has a permanent dipole
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Polar molecule
Has an overall dipole when you take into account any dipoles across the bonds
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Intermolecular force
attractive force between neighbouring molecules
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Permanent dipole-dipole
weak attractive force between permanent dipoles in neighbouring polar molecules
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Van der Waal's
attractive forces between induced dipoles
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Hydrogen bond
A strong dipole dipole attraction between and electron deficient hydrogen atom on one molecule and a lone pair on a highly electronegative atom on a different molecule
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Metallic Bonding
The electrostatic attraction between positive metal ions and delocalised electrons
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Delocalised electrons
shared between more than two atoms
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Giant Metallic Lattice
Three dimensional structure of metal cations and delocalised electrons held together by metallic bonding
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Simple molecular lattice
Three-dimensional structure of molecules bonded by weak intermolecular forces
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Giant covalent lattice
Three-dimensional structure of atoms help together by strong, covalent bonds.
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Period
A horizontal row in the periodic table. Elements show trends in properties across a period.
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Periodicity
regular periodic variation of properties of elements with atomic number and position in periodic table
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Thermal Decomposition
The breaking up of a chemical substance with heat into at least two chemical substances
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Displacement reaction
A reaction in which a more reactive element replaces a less reactive element from an aqueous solution of the latter's ions
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Disproportionation
An oxidation and a reduction of the same element in a redox reaction
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Precipitation reaction
The formation of a solid from a solution during a chemical reaction. Often formed when two aqueous solutions are mixed together
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Hydrocarbon
Organic compound containing carbon and hydrogen only
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Saturated hydrocarbon
Hydrocarbon with single bonds only
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Unsaturated hydrocarbon
Hydrocarbon containing carbon to carbon multiple bonds
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Aliphatic hydrocarbon
Hydrocarbon with carbon atoms joined together in straight or branched chains
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Alicyclic hydrocarbon
Hydrocarbon with carbon atoms joined in a ring structure
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Functional group
The part of the organic molecule responsible for its chemical reactions
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Homologous series
A series of organic compounds with the same functional group but with each successive number differing by CH2
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Alkanes
The homologous series with the genera formula CnH2n+2
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Nomenclature
A system of naming compounds
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Alkyl group
An alkane with a hydrogen atom removed, often shown as R
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General formula
The simplest algebraic formula of a member of the homologous series
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Displayed formula
Shows the relative positioning of all the atoms in a molecule and the bonds between them
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Structural formula
The minimum detail for the arrangement of atoms in a molecule
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Skeletal formula
Simplified organic formula, hydrogens removed from alkly chains, leaving just a carbon skeleton and functional groups
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Structural isomers
Molecules with the same molecular formula but different structural arrangements of atoms
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Sterioisomers
molecules with the same structural formula but different arrangement of atoms in space
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E/Z isomerism
Type of sterioisomerism in which different groups attached to each carbon of a C=C double bond may be arranged differently in space because of the restricted rotation of the C=C double bond
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Cis-Tans isomerism
Special type of E/Z in which there is a non-hydrogen group and a hydrogen on each C in a C=C: The cis(Z) has the H atoms on each carbon on the same side : trans(E) has the H atoms on carbons on the opposite sides
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Homolytic fission
The breaking of a covalent bond with one of the electrons going to each atom, forming two radicals
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Radical
A species with an unpaired electron
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Heterolytic fission
The breaking of a covalent bond with both of the electrons going to only one of the atoms, forming an anion and a cation
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Nucleophile
An atom (or group of atoms) that is attracted to an electron deficient centre or atom where it donates a pair of electrons to form a new covalent bond
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Electrophile
An atom (or group of atoms) that is attracted to an electron-rich centre or atom, it accept a pair of electrons to form a new covalent bond
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Addition reaction
A reactant is added to an unsaturated molecule to form a saturated molecule
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Substitution reaction
An atom or group of atoms is replaced by a different atom or group of atoms
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Elimination reaction
Removal of a molecule from a saturated molecule to form an unsaturated molecule
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Fractional distillation
The separation of components in a liquid mixture into fractions which differ in boiling point by means of distillation, often using a fractioning column
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Cracking
The breaking down of long chained saturated hydrocarbons to form a mixture of shorter alkanes and alkenes
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Catalyst
A substance that increases the rate of a chemical reaction without being used up in the reaction itself
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Radical Substitution
A type of substitution reaction in which a radical replaces a different atom or group of atoms
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Mechanism
A sequence of steps showing the path taken by electrons in a reaction
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Initiation
The first step in radical substitution in which free radicals are generated by UV radiation
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Propagation
The two repeated steps in radical substitution which build up the products in a chain reaction
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Termination
The last step of radical substitution when two radicals combine to form a molecule
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Pi-bond
The reactive part of a double bond formed above and below the plane of bonded atoms by sideways overlap of p orbitals
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Electrophilic addition
A type of addition reaction where an electrophile is attracted to an electron-rich centre or atom, where it accepts a pair of electrons forming a new covalent bond
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Carbocation
An organic ion in which a carbon atom has a positive charge
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Curly arrow
Symbol used in mechanism reactions to show the movement of electrons in the breaking or forming of a covalent bond
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Polymer
A molecular chain made up from monomer units
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Monomer
A small molecule which combines with other monomers to form a polymer
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Addition polymerisation
Unsaturated alkene monomers add onto a growing polymer chain one at a time to form a long polymer chain
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Addition polymer
long molecular chain formed by repeated addition reactions of many unsaturated alkene molecules
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Repeat unit
specific arrangement of atoms that occurs repeatedly in the structure. repeat units are in brackets outside of which lies the symbol n
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Biodegradable material
A material broken down in the environment by living organisms
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Volatility
The ease that a liquid turns into a gas
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Reflux
The continual boiling and condensing of a reaction mixture to ensure the reaction takes place without the contents of the flask boiling dry
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Esterfication
The reaction of an alcohol with a carboxylic acid to produce an ester and water
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Dehydration
elimination reaction in which water is removed from a saturated molecule to make an unsaturated molecule
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Hydrolysis
A reaction with water or aqueous hydroxide ions which breaks a chemical compound into two compounds
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Nucleophilic substitution
a type of substitution reaction in which a nucleophile is attracted to an electron-deficient atom or centre, where it donates a pair of electrons to form a new covalent bond
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Limiting Reagent
The substance in a chemical reaction that runs out first
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Molecular ion
The positive ion formed in mass spectrometry when a molecule loses an electron
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Fragmentation
The process in mass spectrometry which causes a positive ion to split into pieces, one of which is a positive fragment ion
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Enthalpy
The heat content that is stored in a chemical system
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Exothermic
A reaction in which the enthalpy of the product is smaller than that of the reactants, heat loss to the surroundings
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Endothermic
A reaction where the enthalpy of the reactnts is lower than that of the products, heat is drawn in from the surroundings
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Activation energy
The minimum energy required to start a reaction by the breaking of bonds
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Standard conditions
100kPa, 298K, 1.0 mol dm^-3(for aqueous)
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Standard state
Physical state of a substance under the standard conditions
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Enthalpy change of reaction
The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products in their standard states.
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Enthalpy change of combustion
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all products and reactants in their standard states
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Enthalpy change of formation(of a compound)
The enthalpy change when one mole of that compound is formed from its constituent elements in their standard states under standard conditions
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Specific heat capacity
Energy required to raise the temperature of 1g of a substance by 1 degree C
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Bond Enthalpy
The enthalpy change that takes lace when breaking by homolytic fission 1 mole of a given bond in the molecules of a gaseous species
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Average bond enthalpy
Average enthalpy change that takes place when breaking by homolytic fission 1 mole of a given bond in the molecules of a gaseous species
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Hess' law
If a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route
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Rate of reaction
The change in concentration of reactant or product in a given time
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Heterogeneous catalysis
Catalysis of a reaction in which the catalyst has a different physical state from the reactants
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Homogeneous catalysis
Catalysis in which the catalyst and the reactants have the same physical state
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Boltzmann distribution
The distribution of energies of molecules at a particular temperature
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le Chateliers principle
When a system in dynamic equilibrium is subject to a change, the position of the equilibrium will shift to minimise the change
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Dynamic equilibrium
The equilibrium existing in a closed system when the rate of the forward reaction equals that of the reverse reaction
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Greenhouse effect
The process in which the absorbtion and subsequent emission of infrared radiation by atmospheric gases warms the lower atmosphere and the planet's surface
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Troposphere
Lowest layer of the earth's atmosphere
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Stratosphere
Second layer of the earth's atmosphere, containing the o-zone layer
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Adsorbtion
The process that occurs when a gas, liquid, or solute is held to the surface of a solid(possibly a liquid)
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The number of protons in the nucleus of an atom

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Atomic Number

Card 3

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The number of particles(protons and neutrons) in the nucleus

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Preview of the back of card 3

Card 4

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a positively or negatively charged atom or (covalently bonded) group of atoms(a molecular ion)

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Preview of the back of card 4

Card 5

Front

The mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12

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