Chemistry Glossary Term Exams

Justin Ooi Zhi-Wei 1SC4 Chemistry Glossary for term exams 1 Proton number – the number of protons in an atom. Nucleon number – the mass number, the total number of protons and neutrons in an atom. Isotopes – atoms of the same element with the same number of protons but different number of neutrons Relative isotopic mass – the mass of an atom of the isotope relative to 1/12th the mass of a carbon-12 isotope. Relative atomic mass – the average mass of one atom of the lement relative to 1/12th of the carbon-12 isotope. Relative molecule mass – the average mass of one atom of the lement relative to 1/12th of the carbon-12 isotope. Relative formula mass (of a compound) – the sum of the relative atomic masses of all the atoms present in its formula unit. Formula unit – the smallest unit of an ionic compound represented in its formula The Avogadro constant (L of NA) – The number of atoms in exactly 12 g of 12C = 6.02 x 1023 mol-1 The mole – a unit for the amount of substance that contains the Avogadro constant number of like particles (atoms, molecules, ions, electrons) Molar mass – the mass of 1 mole of the substance, expressed in g mol-1 to 1 d.p. Molar volume – volume occupied by 1 mole of the substance in the gaseous state under given conditions of temperature and pressure. Stoichiometric amount – the exact amount of a substance required or produced by a chemical reaction as determined by the coefficients in the balanced equation. Limiting reagent – the reactant that is entirely consumed when the reaction goes to completion. The basicity of an acid – the number of replaceable hydrogen atoms in one molecule of the acid. Avogadro’s hypothesis – Equal volumes of gases, under the same conditions of temperature and pressure contain the same number of molecules. Redox Reaction – A reaction consisting of two half reactions, reduction and oxidation occurring simultaneously.

Oxidation – Addition of oxygen/removal of hydrogen/loss of electron/increase in oxidation state (number) Reduction – Removal of oxygen/addition of hydrogen/gain of electron/decrease in oxidation state (number) Reducing agent – a chemical species which donates electrons (electron donor) for another chemical species to be reduced and itself is oxidized. Oxidizing agent – a chemical species which gains electrons (electron acceptor) from another chemical species to be reduced and itself is reduced. Electronegativity is a measure of the ability of an atom in a molecule to attract a shared pair of electrons in a bond to itself. Disproportionation reaction – A redox reaction in which one species is simultaneously oxidized and reduced. Isoelectronic particles – A group of atoms or ions having the same number of electrons First ionisation energy – the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions with a single positive charge. Enthalpy, H –A state function (i.e. dependent on physical state) that describes the heat content of a system. ∆H – The amount of heat transferred from the system at constant pressure. Enthalpy change of reaction – The heat change in any specific chemical reaction as defined by the stoichiometric thermochemical equation and the value of heat change refers to the amount of substances and their state in that specific equation Calorimetry – A measurement of the heat released or absorbed by a physical change or chemical process. The heat capacity of a substance – The amount of heat required to raise the temperature of the substance by 1 K (1°C) The specific heat capacity of a substance – The amount of heat required to raise the temperature of 1gram of the substance by 1 K (1°C) Standard enthalpy change of formation, ∆Hfθ – The heat change when one mole of substance is formed from its constituent elements in their standard states at 298 K and 1 atmospheric pressure. Standard enthalpy change of combustion, ∆Hcθ – The heat change when one mole of substance is burnt completely in excess oxygen at 298 K and 1 atmospheric pressure.

Hess’ law of Constant Heat Summation – The overall enthalpy change for a reaction is equals to the sum of the enthalpy change of the different individual steps in the reaction, which are measured at the same temperature and pressure. Enthalpy change of atomization – the heat absorbed (endothermic) when one mole of gaseous atoms is formed from the element under standard conditions. Ionisation energy – The heat required to remove one mole of electrons from 1 mole of gaseous atoms/ positive ions to form 1 mol of gaseous positive ions/more positivelycharged ions. Electron affinity – The enthalpy change when gaseous atoms of an element gain 1 mole of electrons to become negative ions. Lattice energy – the heat evolved when one mole of an ionic sold is formed from its component gaseous ions (which at infinite distance apart). It is also the measure of the strength of the electrostatic attraction between oppositely charged ions in the ionic solid. Hydration energy – The heat evolved when one mole of gaseous ions is converted to one mole of aqueous ions at infinite dilution. Enthalpy change of solution – the heat change when one mole of substance (in its substance state) is dissolved in infinite dilution in an aqueous solution. Enthalpy change of neutralization – the heat evolved when one mole of water is made in the reaction between an acid and an alkali under standard conditions. Bond dissocation energy (BDE) – The heat absorbed when one mole of a given bond is broken into gaseous molecules/atom. Entropy is the measure of disorder in a system, showing the distribution of particles at a particular state. Effective nuclear charge, Zeff – The net positive charge (of the nucleus) attracting the electrons in an atom. Nuclear charge – the electrostatic attraction that the positively charged protons exert on the outermost electron Atomic radius – the distance of the outermost orbital occupied by an electron from the nucleus Chemical bond – electrostatic attraction between two entities, typically between a positive charge and a negative charge Metallic bonding – the strong electrostatic forces of attraction between the positive metal ions and mobile sea of delocalized electrons

Ionic bonding – The strong electrostatic forces of attraction between two oppositely charged ions, formed from the transfer of electrons between the original atoms. Covalent bonding – the strong electrostatic attraction between the positive nuclei of the two atoms and the bonding electrons shared between them. Dative covalent bonding – A single covalent bond in which the two bonding electrons are both contributed from only one atom. Electron deficient – An incomplete valence principal quantum shell Adduct – A chemical species consists of 2 different simpler species. Dimer – A chemical species consists of 2 identical simpler species. Bond energy – the energy required to break one mole of covalent bond in a gaseous molecule into constituent gaseous atoms. A sigma bond – a covalent bond formed when 2 singly occupied atomic orbitals containing electrons of opposite spin overlap head-on A pi bond – A covalent bond formed when two singly occupied p-orbitals overlap sideways with one another. Electronic geometry – The three-dimensional arrangement of valence shell electron pairs Molecular geometry – the three dimensional arrangement of atoms around a central atom in a molecule Induced dipole-induced dipole interactions – Weak electrostatic forces of attraction between two temporary dipoles which exist between all types of particles, caused by a momentary polarization of molecules or monoatoms Permanent dipole-permanent dipole interactions – electrostatic forces of attraction between two permanent dipoles which exist between polar molecules, caused by the permanent partial separation of charges Hydrogen bonding – electrostatic forces of attraction between electron-deficient H atom and the very electronegative atom