Chemical Changes & Structure Flashcards
activated complex
a very unstable arrangement of atoms formed at the maximum of the potential energy barrier during a chemical reaction
activation energy
the minimum kinetic energy required by colliding particles before reaction will occur (since a high energy activiated complex must be formed)
adsorption
occurs when molecules become bonded to the surface of a catalyst
allotrope
one of two or more existing forms of an element
e.g. graphite and carbon are allotropes of carbon
bonding electrons
shared pairs of electrons from both atoms forming a covalent bond
chemical bonding
term used to describe the mechanism by which atoms are held together
chemical structure
describes the way in which atoms, ions or molecules are arranged
collision theory
collision theory of reactions suggests that, for a chemical reaction to occur, particles must collide
covalent bond
electrostatic forces of attraction between positively charged nuclei and negatively charged shared pairs of electrons
covalent radius
half the distance between the nuclei of two bonded atoms of an element
delocalised
outer electrons, in metallic bonding, are free from attatchment to any one metal ion and shared amongst the entire structure
allows the metal to conduct
desorption
occurs when the bonds between the molecules on the surface of a catalyst break and the molecules leave the surface of the catalyst
diatomic
molecules with only two atoms
dipole
an atom or molecule in which a concentration of positive charges is separated from a concentration of negative charges
electronegativity
a measure of the attraction that an atom in a bond has for the electrons of the bond
enthalpy change
the change in heat energy when 1 mole of reactant(s) is converted to product(s) at constant pressure
symbol: ∆H units: kJ mol-1
fullerenes
- molecules of pure carbon which form a spherical shape
- it is a discrete covalent molecular substance
hydrogen bonding
type of intermolecular bond which arises when hydrogen bonds with a small, highly electronegative atom like fluorine, nitrogen and oxygen
intermolecular
bonds
forces of attraction which exist between molecules; they are weaker than chemical bonds
intramolecular
bonds
forces of attraction which exist within a molecule
ion
formed when atoms lose or gain electrons to obtain the stable electron arrangement; in general, metal atoms form positive ions and non-metals form negative ions
ionisation energy
the energy required to remove one electron from each atom in one mole of atoms in the gaseous state
isoelectric
atoms/ions which have the same arrangement of electrons are isoelectric
e.g. Na+ and Mg2+
lattice
a regular 3D arrangement of particles in space
metallic lattice, ionic lattice
london dispersion forces
LDFs
the electrostatic force attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules
miscible
fluids which mix with or dissolve in each other in all proportions
non-polar
a molecule where the electronegativities are such that no permanant dipole is formed
O=C=O
<-+ +->
periodicity
the regular recurrance of similar properties when the elements are arranged in order of increasing atomic number
permanant dipole to permanent dipole
- when a molecule has an uneven distribution of electrons due to a difference in electronegativites a permanent dipole is formed
- opposite dipoles attract to form permanent dipole to permanent dipole bonds
physical properties
properties that can be measured without changing the chemical identity of a substance
e.g. melting point, boiling point
polar covalent
a molecule containing covalent bonds between atoms of different electronegativity, which results in an uneven distribution of electrons and a partial charge along the bond
properties
physical and chemical characteristics of a substance
often reflection on bonding and sturcture
viscosity
the resistance to flow that is shown by all liquids
