CHEMISTRY KEYWORDS:
Unified atomic mass unit: One-twelfth of the mass of a carbon-12 atom.
Relative isotopic mass: The mass of a particular atom of an isotope compared to the value of the unified atomic mass unit.
Formula unit: The simplest formula for a covalent giant structure or an ionic giant structure.
Relative molecular mass, Mr: The weighted average mass of a molecule in a given sample of that molecule compared to the value of the unified atomic mass unit.
Relative formula mass, Mr: The weighted average mass of one formula unit compared to the value of the unified atomic mass unit.
Water of crystallization: A specific number of moles of water associated with a crystal structure.
Hydrated compound: A compound that contains a definite number of moles of water in their structure (water of crystallization).
Anhydrous: Containing no water of crystallization.
Relative isotopic abundance: The proportion of one particular isotope in a mixture of isotopes, usually expressed as a percentage. The heights of the peaks in a mass spectrum show the proportion of each isotope present.
Molecular ion: The ion that is formed by the loss of an electron from the original complete molecule during mass spectrometry. This gives us the relative molecular mass of an unknown compound.
Fragmentation: The breaking up of a covalent compound during mass spectrometry into smaller positively charged species.
Molecular formula: The formula that shows the number and type of each atom in a molecule.
Avogadro constant, L: The number of specified particles (atoms, molecules, ions or electrons) in a mole of those particles. Its numerical value is 6.02 x 1023.
Molar mass: The mass of a mole of substance in grams.
Stoichiometry: The mole ratios of reactants and products shown in the balanced equation.
Empirical formula: The simplest whole number ratio of the elements present in one molecule or formula unit of the compound.
Compound ion: an ion containing more than one type of element.
State symbol: In a chemical equation a symbol (sign) placed after each reactant and product in a chemical equation to indicate whether they are solid (s), liquid (l), gas (g), or in aqueous solution (aq).
Spectator ions: Ions present in a reaction mixture which do not take part in the reaction.
Ionic equation: A balanced equation showing only those ions, atoms or molecules taking part in the reaction. Spectator ions are not shown. Ionic equations are often written for reactions involving a change in oxidation state.
Solute: A substance which dissolves in a solvent to form a solution.
Solvent: A substance which dissolves a solute to form a solution.
Titre: In a titration, the final burette reading minus the initial burette reading.
Solution concentration: The amount of solute (in moles) dissolved in a stated volume of solution (usually 1.00 dm3).
Molar gas volume: The volume occupied by one mole of any gas at room temperature and pressure (r.t.p). One mole of gas occupies 24.0 dm3 at r.t.p.
CHEMISTRY DEFINITIONS:
Relative atomic mass, Ar: The weighted average mass of atoms in a given sample of an element compared to the value of the unified atomic mass unit.
Mole: The amount of substance which contains 6.02 x 1023 specified particles (atoms, molecules, ions or electrons).
Oxidation number (oxidation state): A number given to an atom or ion in a compound that describes how oxidised or reduced it is.
CHEMISTRY IMPORTANT NOTES:
1 unified atomic mass unit = 1 u = 1.66 x 10-27 kg
SUMMARY:
The unified atomic mass unit is one-twelfth of the mass of a carbon-12 atom.
Relative atomic mass is the ratio of the weighted average mass of atoms in a given sample of an element to the unified atomic mass unit.
The mass spectrometer can be used to determine atomic masses and isotopic abundances, to deduce the molecular mass of an organic compound and to deduce the formula of an organic molecule from its fragmentation pattern and isotopic ratios.
One mole of a substance is the amount of substance that has the Avogadro number of specified particles. (6.02 x 1023). The particles can be atoms, molecules, ions or electrons).
Molecular formulae show the total number of atoms of each element present in one molecule or one formula unit of the compound. Empirical formulae show the simplest whole-number ratio of atoms in a compound.
The mole concept can be used to calculate:
- Reacting masses
- Volume of gases
- Volumes and concentrations of solution
The stoichiometry of a reaction can be obtained from the calculations involving reacting masses, gas volumes, and volumes and concentrations of solutions.
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