Chemistry definition

Question 1

Isotopes:

Answer 1

Atoms, whose nuclei have the same atomic number (Z), but different mass number (A). (different neutron number.)

Question 2

Principal quantum number:

Answer 2

Determine the distance from the nucleus. Identifies the shell.

Question 3

Angular quantum number:

Answer 3

Determine the shape of the orbitals belonging to the subshell

Question 4

Magnetic quantum number:

Answer 4

Orientation of the orbitals in magnetic field

Question 5

Spin quantum number:

Answer 5

Refers the two possible orientation of the spin of an electron. Identifies the electron.

Question 6

Pauli’s exclusion principle:

Answer 6

No two electrons can have the same four quantum numbers in an atom.

Question 7

Hund’s rule:

Answer 7

(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.

Question 8

Building-up principle:

Answer 8

Means that the subshellsare built up in an order as the energy of the subshells increases (E n+ 0.7l).

Question 9

Rules to determine the oxidation numbers:

Answer 9

1. The oxidation number of atoms in elements is zero.
2. 2. 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).
3. 3. 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).
4. 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.

Question 10

Molar volume:

Answer 10

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.

Question 11

Avogadro’s law:

Answer 11

Equal volumes of all gases, at the same temperature and pressure, have the same number of molecules

Question 12

The Lewis acid- base concept:

Answer 12

• 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.

Question 13

Reaction rate:

Answer 13

Change in amount(or concentrationat const. volume) of a reactant or product in a given unit of time

Question 14

Catalysts:

Answer 14

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

Question 15

Ionization energy:

Answer 15

The amount of energy required to completely removing the most loosely held electron from the gaseous atom (units are: J, eV, or J/mol).

Question 16

Bond order:

Answer 16

The half of the difference between the number of bonding-, and antibonding electrons in the given molecule. For O2: (10 – 6)/2 = 2

Question 17

Isomerism:

Answer 17

Compounds having an identical composition and molecularmass, but different structure, and different physical andchemical properties

Question 18

Constitutional isomerism:

Answer 18

Molecules having same molecular formula, but different order of atomic connections, are referred to as constitutional isomers. (Different structures with different properties)

Question 19

Conformation:

Answer 19

Specific arrangement of atoms within a molecule, emerging from the free rotation around the C-C single bonds, is called conformation.

Question 20

Cracking:

Answer 20

Transformation of high boiling hydrocarbons into simpler hydrocarbons of shorter carbon chain

Question 21

Markovnikov’s rule:

Answer 21

When an unsymmetrically substituted alkene reactswith a hydrogen halide, the hydrogen adds to the carbon that has greater number of hydrogen substituents.

Question 22

Elimination:

Answer 22

The reaction that occurs when a single reactant splits apart into two products

Question 23

Homogeneous equilibria:

Answer 23

All reacting componentsare in the same phase

Question 24

Heterogeneous equilibria:

Answer 24

Equilibria between substances in two or more phases.

Question 25

Le Chatelier- Braun principle:

Answer 25

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.

Question 26

Arrhenius concept:

Answer 26

• Acid: a compound that produces H+ ions in water

* Base: a compound that produces OH- ions in water

Question 27

Brönsted- Lowry concept:

Answer 27

Acid, BH:
- A compoundthat can donate proton
(proton donor)

Base, B:
- A compoundthat can accept a proton
(proton acceptor)

Question 28

Buffer solutions:

Answer 28

A buffer solution is capable of maintaining its pH at nearly constant value even whensmallamountsofstrongacidor-base are added.

Question 29

Lewis concept:

Answer 29

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.

Question 30

Molality:

Answer 30

Quantity of substance B divided by mass of solvent. It is a temperature independent concentration. Its symbol is mB

Question 31

Mass concentration:

Answer 31

The mass concentration of substance B divided by the volume of solution.

Question 32

Mole fraction:

Answer 32

Quantity of substance B divided by the total quantity of matter in the solution.

Question 33

Mass fraction:

Answer 33

Mass of substance B divided by mass of mixture.

Question 34

Volume fraction:

Answer 34

Volume of substance B divided by volume of mixture.

Question 35

Mass %:

Answer 35

g of solute in 100g of solution

Question 36

Mol %:

Answer 36

Mol of solute in 100mol of solution.

Question 37

Mixed %:

Answer 37

g of solute in 100cm3 solution

Question 38

Ionization energy:

Answer 38

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.

Question 39

Electron affinity:

Answer 39

The energy change (E) associated with the process in which an electron is added to a gaseous atom in its ground state.

Question 40

Electronegativity:

Answer 40

Is a chemical property that describes the tendency of an atom to attract electron density towards itself.

Question 41

Lattice energy:

Answer 41

The energy required to convert the crystal into infinitely separated gaseous ions, in vacuum(an endothermic process).Unit: kJ/mol

Question 42

Octet rule:

Answer 42

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.

Question 43

Stereoisomers:

Answer 43

Isomers that differ in spatial (three dimensional) arrangement of their atoms

Question 44

Chiral molecule:

Answer 44

A molecule (or object) that is not superimposable on its mirror image is said to be chiral.

Question 45

Enantiomers:

Answer 45

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.

Question 46

Optical activity:

Answer 46

Is the abiliity of a substance to rotate of the plane of polarized light

Question 47

Diastereomers:

Answer 47

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