Definitions Flashcards
Daltons atomic theory
All matter is made up of very small particles called atoms
All atoms are indivisible. They cannot be broken down into smaller particles.
Cathode rays
Streams of negatively charged particles called electrons.
Energy level
The fixed energy value an electron can have in an atom
Ground state
State where an electron occupies lowest energy level available
Excited state
State where an electron occupies a higher energy level than those available in the ground state
Heisenbergs uncertainty principle
It is not possible to measure at the same time both the velocity and position of an electron in an atom
Orbital
Fixed region of space where there is a high probability of finding an electron
Sub level
A subdivision of a main energy level that consists of one or more orbitals of the same energy
Element
Substance that cannot be split into simpler substances by chemical means
Dobereiners triad
A triad is a group of 3 elements with similar properties in which the atomic weight of the middle element is approximately equal to the average of the other two
Newlands octaves
The arrangement of elements in which the first and eight elements counting from a particular element have similar properties
Mendeleevs Periodic law
When elements are arranged in order of increasing atomic weight, the properties of the elements recur/ repeat periodically in columns (groups) of similar chemical properties
Atomic number
Number of protons in the nucleus of an atom
Modern periodic law
When elements are arranged in order of increasing atomic number the properties of the elements recur/repeat periodically
Mass number
Sum of the number of protons and neutrons in the nucleus of an atom of that element
Isotopes
Atoms of the same element so they have the same atomic number due to the same number of protons but differing mass number due to the different number of neutrons in the nucleus
Relative atomic mass
The average mass number of the isotopes of an element as they occur naturally taking their abundance’s into account and expressed on a scale in which the atoms of the carbon 12 isotope have a mass of exactly 12 units
Principle of mass spectrometry
Charged particles moving in a magnetic field are deflected and separated by different extents/ amounts according to their masses
Electron configuration
Shows the 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
Hunds rule of maximum multiplicity
When two or more orbitals of equal energy are available electrons occupy singly before occupying them in pairs
Paulis exclusion principle
No more than two electrons can occupy and orbital and the electrons must have opposite spin
Compound
Substance that is made up of two or more different elements that are chemically combined e.g. Water, carbon dioxide, ammonia, methane
Octet rule
When bonding happens, atoms tend to reach an electron arrangement with eight electrons in the outermost energy level
Ion
Charged atom or group of atoms
Ionic bond
Force of attraction between oppositely charged ions in a compound
Always formed by the complete transfer of electrons from one atom to another
Transition metal
Metal that forms at least one ion with a partially filled d sub level
Molecule
Group of atoms joined together.
Smallest particle of an element or compound that can exist independently
Valency
Number of atoms of hydrogen or any other monovalent element with which each atom of the element combines
E.g. carbon can bond to 4H atoms so it has a valency of 4
Sigma bond
Formed by the head on overlap of molecular orbitals
Pi bond
Formed by the sideways overlap of p,d and forbitals
Electronegativity
Relative attraction an atom in a molecule has
For the shared pair of electrons in a covalent bond
Polar Covalent Bond
A polar covalent bond is a bond in which there is unequal sharing of the pair of electrons. This causes one end of the bond to be partially positive and the other end to be partially negative.
Intramolecular Bonding
Bonding that takes place within a molecule.
It holds atoms in a molecule together
E.g covalent bonding
Intermolecular Forces
Forces of attraction between different molecules
E.g Van der Waals, hydrogen bonding,dipole-dipole
VAn der Waals
Weak forces of attraction between molecules //
Resulting from the formation of temporary dipoles.
Dipole-dipole Forces
Forces of attraction between the negative pole of one polar molecule
And the possitive pole of another polar molecules.
Hydrogen Bond
Particular dipole-dipole attractions between molecules where the hydrogen atom bonded to either nitrogen, fluorine or oxygen.
The H atom carries a partial positive charge and is attracted to a partial negative charge in a nearby polar molecule.
Half-life
Time taken for half of the nuclei in a given sample to decay.
Law of Conservation of Matter
The law of conservation of matter states that in any chemical reaction matter is neither creatednor destroyed, but merley changed from one form to another.
Atomic Radius
Half the distance between the nuclei of two atoms of the same element
That are joined together by a single covalent bond.
First Ionisation Energy
Minimum energy required to completely remove the most loosely bound electron //
From a neutral gaseous atom in its ground state
E.g Na (g) - Na +(g)+e
Second Ionisation Energy
Energy required to completely remove an electron from an ion with positive charge
In the gaseous state
E.g Ca+(g)-Ca+2(g)+e
Radioactivity
Spontaneous breaking up of unstable nucleiWith the emission of one or more types of radiation
Nuclear Reaction
Process that alters the composition, structure or energy of an atomic nucleus.
Mole
Is an amount used in chemistry
A mole of a substance is the amount of that substance that contains 6x10 (23) particules of that substance.
Relative molecular mass (RMM)
Average mass of one molecule of that compound compared with one twelfth the mass of one atom of the carbon-12 isotape.
Gas
Substance that has no well-defined boundary
But diffuses rapidly to fill the container in which it is pleased.
Boyle’s Law
At 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 its temperature as measured on the kelvin scale
Gay-Lussac’s Law of Combining Volumes
In a reaction between gases, the volume of the reacting gases and the volumes of any gaseous products are in the ratio of small whole numbers
Provided the volumes are measured at the same temperature and pressure.
Avogadro’s Law
Equal volumes of gases contain equal numbers of molecules under the same conditions of temperature and pressure.
Ideal Gas
A Gas that perfectly obeys all of the assumptions of the kinetic theory of gases under all conditions of temperature and pressure.
Real Gases
Different from am ideal gasbecause forces of attraction and repulsion do exist between molecules and The volume of the molecules is not always negligible.
Molecular formula
The formula which shows the number and type of each atom present in a molecule of that compound
Empirical formula
This is the simplest whole number ratio of atoms or ions of each element in a substance
Arrhenius’s acid
Substance that dissociates in water go from H+ ions
Arrhenius’s base
Substance that dissociates in water to form OH- ions
Arrhenius’s strong vs weak acid
Strong acid: almost completely dissociates in water to from H+ ions
Weak acid: slightly dissociates in water to form H+ ions
Arrhenius’s strong vs weak base
Strong base: almost completely dissociates in water to form OH- ions
Weak base: slightly dissociates in water to form OH-ions
Brønsted-Lowry acid, strong acid, weak acid
Acid = proton donor
Strong acid=good proton donor
Weak acid = poor proton donor
Conjugate acid base pair
Any pair consisting of an acid and a base that differ by a proton.
An acid becomes its conjugate base after it has donated a proton.
Salt
Substance formed when a hydrogen ion from an acid is replaced by a metal or an ammonium ion
Neutralisation
Reaction between an acid and a base to produce a salt and water
Solution
Completely perfect mixture of a solute and a solvent.
In a solution, the solute particles are uniformly distributed throughout the solvent I.e. the solution is homogenous
Concentration
Amount of solute dissolved in a given volume of solution
Standard solution
Solution which concentration is accurately known
Primary standard
Substance that can be obtained in a stable pure, soluble solid
So that it can be weighed out and dissolved in water to give a solution of accurately known concentration
Titration
An experiment, the measured volume of one solution is added to the known volume of another solution until the reaction is complete
Usually Indicated with a colour change (If an indicator is present)
Oxidation
Oxidation is loss of electrons.
Increase in oxidation number
Oxidising agent
Substance that causes something else to be oxidised.
The oxidising agent itself will be reduced
Reduction
Reduction is loss of electrons
Decrease in oxidation number
Reducing agent
Substance that causes something else to be reduced
The reducing agent itself will be oxidised
Oxidation number
Charge that an atom has or appears to have after electrons have been distributed according to certain rules
Rate of reaction
Change in concentration of any one reactant or product per unit time
Or
Change in concentration
————————————
Time
Instantaneous rate of reaction
Rate of reaction at any one particular time during a reaction
Catalyst
Substance that alters the rate of a chemical reaction but is not consumed in the reaction
Enzyme
Substance that is produced by a living cell and acts as a biological catalyst
Homogenous catalysis
Catalysis in which both the reactants and the catalyst are in the same phase (I.e. there is no boundary between the reactants and the catalyst)
KEY:PHASE IS NOT THE SAME AS STATE. DO NOT SAY STATE
Heterogeneous catalysis
Catalysis in which both the reactants and the catalyst are in different phases (I.e. there is a boundary between the reactants and the catalyst)
Autocatalysis
Catalysis in which one of the products of the reaction acts as a catalyst for the reaction
Catalytic converter
Device that is fitted to the exhaust system of a motor vehicle which contain catalysts to convert pollutants in the exhaust gases to less harmful substances
Catalytic poison
Substance that makes a catalyst inactive by sticking to the surface of the catalyst, blocking the active site
Effective collision
Collision that results in the formation of products
Activation energy
Minimum energy that colliding particles must have in order for a chemical reaction to occur
Reaction profile diagram
Graph which shows the change in energy of a chemical reaction over time as the reaction progresses
Reversible reaction
One in which the products react to give back the reactants I.e. the reaction is going in both directions
Chemical equilibrium
State of dynamic balance in a reversible reaction where the rate of forward reaction is equal to the rate of reverse reaction
Dynamic state
Reactants are continuously forming products and the products are continuously forming reactants
Dynamic equilibrium
Rate of forward reaction is equal to the rate of the reverse reaction
Le chateliers principle
If a stress is applied to a system in equilibrium, the system readjusts to relieve the stress applied
Equilibrium constant (Kc) for Haber Bosch reaction
N2 + 3H2 2NH3
Kc= [NH3]2
———-
[N2][H2]3
Self ionisation of water/ ionic product of water (Kw)
H2O H+ + OH-
Kw = [H+][OH-]
Key: never write H2O in the Ka, Kb, Kw expressions
pH
pH= -log10[H+]
Dissociation of an acid (HCL) in water
HCL + H2O H3O+ + Cl-
Acid dissociation constant (Ka)
HCL + H2O H3O+ Cl-
Ka =[H3O+][Cl-]
—————-
[HCl]
pOH
pOH = -log10[OH-]
Acid- base indicator
Substance that changes colour according to the pH of the solution in which it is placed
Indicator range
pH interval over which there is a clear change in colour for that indicator
Hard water
Water that does not form a lather easily with soap. Forms a scum instead
Caused by Mg+2 or Ca+2 ions
Temporary hardness
Hardness that can be removed by boiling
Caused by the presence of calcium hydrogencarbonate
Permanent hardness
Hardness that cannot be removed by boiling
Caused by the presence of magnesium sulphate
Buffer solution
Solution that resists changes in pH. It keeps the pH of a solution constant
Flocculation
Coagulation of small suspended particles in water, to form larger particles which settle to the bottom of the tank
B.O.D Biochemical Oxygen Demand
BOD is the amount of dissolved oxygen in p.p.m consumed by biological action, when a sample of water is stored in the dark at 20•C for 5 days
Eutrophication
Enrichment of water with nutrients which leads to excessive growth of algae and other plants
Primary treatment of sewage
Mechanical process in which large solids are removed by screening and some suspended solids are removed by sedimentation
Secondary treatment of sewage
- Biological oxidation process where the levels of suspended and dissolved organic material is reduced
- sewage is decomposed by bacteria which use nutrients from the sewage together with oxygen from the air to break down the sewage
Tertiary treatment of sewage
- process involving the removal of phosphorus compounds by precipitation
- and the removal of nitrogen compounds by biological ion-exchange methods
Principle of colorimetry
Amount of absorbance of light by a coloured solution is proportional to the concentration of the solution
Electrolysis
Use of electricity to make a chemical reaction happen in an electrolyte
Electrolyte
Compound, when molten or dissolved in water, will conduct an electric current
Electroplating
An electrolyte is used to put a layer of one metal on the surface of another metal
Electrochemical series
List of elements in order of their standard electrode potentials
Organic chemistry
Organic chemistry is the study of compounds of carbon
Hydrocarbon
Compound that contains hydrogen and carbon only
Fossil fuels
Fuels that were formed from the remains of plants and animals that lived millions of years ago
Homologous series
- a series of compounds of similar chemical properties
- showing gradations in physical properties
- having the same general formula for it’s members
- each member has a similar method of preparation
- each member differs from the previous member by a CH2 unit
Structural isomer
Compounds with the same molecular formula but different structural formulas
Unsaturated compound
One that contains one or more double or triple bonds between atoms in the molecule
Aliphatic compound
An organic compound that consists of open chains of carbon atoms and closed chain compounds (rings) that resemble them in chemical properties
Aromatic compound
Compounds that contain a benzene ring structure in their molecules
Auto-ignition
The premature ignition of the petrol air mixture before normal ignition of the mixture by a spark takes place
Octane number
A measure of the tendency of a fuel to resist knocking
Catalytic cracking
The breaking down of long chain hydrocarbon molecules, by the action of heat and catalysts, into short chain molecules for which there is great demand
Heat of reaction
The heat change when the number of moles of reactants indicated in the balanced equation for the reaction react completely
Heat of combustion
The heat change when one mole of a substance is completely burned in excess oxygen
Bond energy
The average energy required to break one mole of a particular covalent bond and to separate the neutral atoms completely from each other
Kilogram calorific value
The heat energy produced when 1kg of the fuel is completely burned in oxygen
Heat of neutralisation
The heat change when one mole of H+ ions from an acid react 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’s law
If a chemical reaction takes place in a number of stages, the sum of the heat changes in the separate steps is equal to the heat change if the reaction is carried out in one stage
Law of conservation of energy
Energy cannot be created nor destroyed but can only be converted from one form of energy into another
Chloroalkane
A compound in which one or more of the hydrogen atoms in the alkane molecule have been replaced by chlorine atoms
Functional group
A functional group is an atom or group of atoms which are responsible for the characteristic properties of an organic compounds or a series of organic compounds
Primary alcohol
A primary alcohol is one where the carbon atom joined to the OH group is attached to only one other carbon atom
Secondary alcohol
A secondary alcohol is one where the carbon atom joined to the -OH group is attached to two other carbon atoms
Tertiary alcohol
A tertiary alcohol is one where the carbon atom joined to the OH group is attached to three other carbon atoms
Condensation reaction
A chemical reaction in which two molecules combine to form a larger molecule with the loss of a smaller molecule such as water
Steam distillation
A separation process used to isolate compounds at temperatures below their decomposition temperatures. It is carried out by bubbling steam through the material and distilling off the immiscible liquids
Emulsion
A dispersion of small droplets of one liquid in another liquid in which it is not soluble
Liquid-liquid extraction
A technique in which two immiscible liquids (e.g. oil of cloves and water) are separated using a solvent (e.g. cyclohexane) in which one of the components of the mixture (clove oil) has a higher solubility than the other (water). The organic component is removed from the emulsion by dissolving the organic component in an organic solvent.
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
The detailed step by step description of how the 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 another step of the reaction
Addition reaction
One in which two or more molecules react together to form a single molecule
Polymer
Long chain molecules made by joining together many small molecules (monomers)
The repeating unit of a polymer
Part of the polymer that repeats and completes the polymer chain (except for the end groups)
Elimination reaction
One in which a 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 materials
Recrystallisation
A process of repeated crystallisation in order to purify a solid or to obtain more satisfactory crystals of a solid that is already pure
Chromatography
A separation technique in which a mobile phase carrying a mixture moves in contact with a selectively adsorbent stationary phase
Principle of chromatography
The principle on which all chromatographic separation techniques are based is that separation of a mixture of components occurs as a result of selective adsorbance of the components of the mixture on a stationary phase while carried by a mobile phase
Principle of gas chromatography
The principle of gas chromatography is that a gaseous mobile phase is in contact with a stationary phase (non volatile liquid) and separation of the mixture occurs as a result of selective adsorbance of the components of the mixture on the stationary phase
Principle of HPLC
The principle of high performance liquid chromatography is that a liquid mobile phase is in contact with a stationary phase (fine particles of a solid) and separation of the mixture occurs as a result of selective adsorbance of the components of the mixture on the stationary phase
Principle of IR spectrometry
The principle of Infra-red spectrometry is that organic compounds absorb infra-red radiation of certain frequencies. The combinations of frequencies that are absorbed depend on the bonding within the molecule and are unique to a particular molecule
Principle of UV absorption spectrometry
The principle of ultraviolet absorption spectrometry is that absorbance is directly proportional to the concentration of a substance
Properties of cathode rays
- travel in straight lines from cathode to anode
- can be deflected In electric and magnetic fields
- have sufficient energy to move a small object such as a paddle wheel
