Chemistry definition Flashcards
Isotopes:
Atoms, whose nuclei have the same atomic number (Z), but different mass number (A). (different neutron number.)
Principal quantum number:
Determine the distance from the nucleus. Identifies the shell.
Angular quantum number:
Determine the shape of the orbitals belonging to the subshell
Magnetic quantum number:
Orientation of the orbitals in magnetic field
Spin quantum number:
Refers the two possible orientation of the spin of an electron. Identifies the electron.
Pauli’s exclusion principle:
No two electrons can have the same four quantum numbers in an atom.
Hund’s rule:
(the rule of maximum multiplicity):
States that the electrons are distributed among the orbitals of a subshell in a way that gives the maximum number of unpaired electrons with parallel spins.
Building-up principle:
Means that the subshellsare built up in an order as the energy of the subshells increases (E n+ 0.7l).
Rules to determine the oxidation numbers:
- The oxidation number of atoms in elements is zero.
- The oxidation number of alkali metals(column I. in periodic system)is always +1 (except elemental form).The oxidation number of alkali earth metals(column II. in periodic system) is always +2(except elemental form).The oxidation number of aluminiumis +3(except elemental).
- The oxidation number of hydrogen usually +1 (except elemental form) and hydrides, when it is -1 (e.g. LiH, CaH2, etc.). The oxidation number of oxygen usually is -2(except elemental form) and peroxides, when it is -1 (e.g. H2O2).
- In molecules the algebraic sum of the oxidation numbers of atoms equals zero. In case of ions the sum of oxidation numbers equals the electrical charge of the ion.
Molar volume:
The molar volume (Vm) is the volume occupied by one mole of a substance (chemical element or chemical compound) at a given temperature and pressure.
Avogadro’s law:
Equal volumes of all gases, at the same temperature and pressure, have the same number of molecules
The Lewis acid- base concept:
- Lewis-bases aremolecules or anions, that have lone electron pair(s)with which it can form covalent, dativebond (electronpair donors),
- e.g.ammonia, water, hydroxide ion, cyanide ion, halide ions, etc.
- Lewis-acids are molecules or cations that can form a covalent, dativebond by accepting an electron pair from a base (electron pair acceptors),
- e.g.boron trifluoride, proton, aluminum(III)ion, carbon dioxide, copper(II) ion, sulfur trioxide, etc.
Reaction rate:
Change in amount(or concentrationat const. volume) of a reactant or product in a given unit of time
Catalysts:
A catalyst is a substance that increases the rate of a chemical reaction without being used up in the reaction.
The catalyst, C:
- maybe recovered unchanged at the end of the reaction
- small amount is enough to accelerate a reaction -cannot initiate thermodynamically not allowed reactions
Ionization energy:
The amount of energy required to completely removing the most loosely held electron from the gaseous atom (units are: J, eV, or J/mol).
Bond order:
The half of the difference between the number of bonding-, and antibonding electrons in the given molecule. For O2: (10 – 6)/2 = 2
Isomerism:
Compounds having an identical composition and molecularmass, but different structure, and different physical andchemical properties
Constitutional isomerism:
Molecules having same molecular formula, but different order of atomic connections, are referred to as constitutional isomers. (Different structures with different properties)
Conformation:
Specific arrangement of atoms within a molecule, emerging from the free rotation around the C-C single bonds, is called conformation.
Cracking:
Transformation of high boiling hydrocarbons into simpler hydrocarbons of shorter carbon chain
Markovnikov’s rule:
When an unsymmetrically substituted alkene reactswith a hydrogen halide, the hydrogen adds to the carbon that has greater number of hydrogen substituents.
Elimination:
The reaction that occurs when a single reactant splits apart into two products
Homogeneous equilibria:
All reacting componentsare in the same phase
Heterogeneous equilibria:
Equilibria between substances in two or more phases.
Le Chatelier- Braun principle:
A system in equilibrium reacts to a change (stress) in conditions in a way that counteractsthe applied change and establishes a new equilibrium state. Each change in the conditions (concentration, temperature, etc.) should be considered a stress.
Arrhenius concept:
- Acid: a compound that produces H+ ions in water
* Base: a compound that produces OH- ions in water
Brönsted- Lowry concept:
Acid, BH:
- A compoundthat can donate proton
(proton donor)
Base, B:
- A compoundthat can accept a proton
(proton acceptor)
Buffer solutions:
A buffer solution is capable of maintaining its pH at nearly constant value even whensmallamountsofstrongacidor-base are added.
Lewis concept:
Lewis-bases are molecules or ions, that have unshared electron pair(s)with which it can form covalent bond
(electron pair donors),
- e.g.ammonia, water, hydroxide ion, etc.
Lewis-acids are molecules or ions that can form a covalent bond by accepting an electron pair from a base
(electron pair acceptors),
- e.g.boron trifluoride, proton, aluminum(III)ion, carbon dioxide, copper(II) ion, etc.
Molality:
Quantity of substance B divided by mass of solvent. It is a temperature independent concentration. Its symbol is mB
Mass concentration:
The mass concentration of substance B divided by the volume of solution.
Mole fraction:
Quantity of substance B divided by the total quantity of matter in the solution.
Mass fraction:
Mass of substance B divided by mass of mixture.
Volume fraction:
Volume of substance B divided by volume of mixture.
Mass %:
g of solute in 100g of solution
Mol %:
Mol of solute in 100mol of solution.
Mixed %:
g of solute in 100cm3 solution
Ionization energy:
The amount of energy required to remove the most loosely held electron from an isolated atom in its ground state is called first ionization energy.
Electron affinity:
The energy change (E) associated with the process in which an electron is added to a gaseous atom in its ground state.
Electronegativity:
Is a chemical property that describes the tendency of an atom to attract electron density towards itself.
Lattice energy:
The energy required to convert the crystal into infinitely separated gaseous ions, in vacuum(an endothermic process).Unit: kJ/mol
Octet rule:
States that atoms of low atomic number tend to combine(with covalent or ionic bond)in such a way that they each have eight electrons in their valence shells, giving them the same electron configuration as a noble gas.
Stereoisomers:
Isomers that differ in spatial (three dimensional) arrangement of their atoms
Chiral molecule:
A molecule (or object) that is not superimposable on its mirror image is said to be chiral.
Enantiomers:
They are isomers differing only in the three-dimensional arrangement of substituents. These stereoisomers are called enantiomers. Enantiomers are mirror images that are not superimposable.
Optical activity:
Is the abiliity of a substance to rotate of the plane of polarized light
Diastereomers:
Are no mirror image isomers in general case:
- At least one chiral center should have the same configuration,
- At least one chiral center should have the opposite configuration
