Unit 1 definitions

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AS Level OCR A Chemistry
Steph Keogh
Flashcards by Steph Keogh, updated more than 1 year ago
Steph Keogh
Created by Steph Keogh about 10 years ago
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What is an isotope? An atom of the same element with a different number of neutrons.
What is atomic (proton) number? The number of protons in the nucleus of an atom.
What is mass (nucleon) number? The number of particles (protons and neutrons) in the nucleus.
What is an ion? A positively or negatively charged atom or group of atoms.
What is relative isotopic mass? The mass of an atom of an isotope compared with one twelfth of the mass of an atom of Carbon-12.
What is relative atomic mass? The weighted mean mass of an atom of an element compared with one twelfth of the mass of an atom of Carbon-12.
What is relative molecular/relative formula mass? The weighted mean mass of a molecule/formula unit compared with one twelfth of the mass of an atom of Carbon-12.
What is amount of substance? The quantity whose unit is the mole. It is used as a means of counting atoms.
What is the Avogadro constant? The number of atoms per mole of the Carbon-12 isotope.
What is a mole? The amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the Carbon-12 isotope.
What is molar mass? The mass per mole of a substance (units g/mol).
What is empirical formula? The simplest whole-number ratio of atoms of each element present in a compound.
What is a molecule? A small group of atoms held together by covalent bonds.
What is molecular formula? The actual number of atoms of each element in a molecule.
What is molar volume? The volume per mole of a gas. At room temperature and pressure, the molar volume is approximately 24.0 dm^3 mol^-1.
What is concentration? The amount of solute, in mol, dissolved per litre of solution.
What is a standard solution? A solution of known concentration. They are normally used in titrations to determine unknown information about another substance.
What is a species? Any type of particle that takes part in a chemical reaction.
What is stoichiometry? The molar relationship between the relative quantities of substances taking part in a reaction.
What is an acid? A species that is a proton donor.
What is a base? A species that is a proton acceptor.
What is an alkali? A type of base that dissolves in water forming hydroxide ions.
What is a salt? Any chemical compound formed from an acid when a H+ ion from the acid has been replaced by a metal ion or another positive ion.
What is a cation? A positively charged ion.
What is an anion? A negatively charged ion.
What does hydrated mean? It refers to a crystalline compound containing water molecules.
What does anhydrous mean? It refers to a substance that contains no water molecules.
What is water of crystallisation? It refers to water molecules that form an essential part of the crystalline structure of a compound.
What is an oxidation number? A measure of the number of electrons that an atom uses to bond with atoms of another element. They are derived from a set of rules.
What is oxidation? Loss of electrons or increase in oxidation number.
What is reduction? Gain of electrons or a decrease in oxidation number.
What is a reducing agent? A reagent that reduces (adds electrons to) another species.
What is an oxidising agent? A reagent that oxidises (takes electrons from) another species.
What is first ionisation energy of an element? The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.
What is electron shielding? The repulsion between electrons in different inner shells. Shielding reduces the net attractive force from the positive nucleus on the outer-shell electrons.
What are successive ionisation energies? A measure of the energy required to remove each electron in turn.
What is a shell? A group of atomic orbitals with the same principal quantum number, n. Also known as the main energy level.
What is principal quantum number? A number representing the relative overall energy of each orbital, which increases with distance from the nucleus. The sets of orbitals with the same n-value are referred to as electron shells or energy levels.
What is an atomic orbital? A region within an atom that can hold up to two electrons, with opposite spins.
What is a sub-shell? A group of the same type of atomic orbitals (s, p, d or f) within a shell.
What is electron configuration? The arrangement of electrons in an atom.
What is a compound? A substance formed from two or more chemically bonded elements in a fixed ratio, usually shown by a chemical formula.
What is an ionic bond? The electrostatic attraction between oppositely charged ions.
What is a giant ionic lattice? A three-dimensional structure of oppositely charged ions, held together by strong ionic bonds.
What is a group? A vertical column in the Periodic Table. Elements in the same group have similar chemical properties and their atoms have the same number of outer-shell electrons.
What is a covalent bond? A bond formed by a shared pair of electrons.
What is a lone pair? An outer-shell pair of electrons that is not involved in chemical bonding.
What is a dative covalent/coordinate bond? A shared pair of electrons which has been provided by one of the bonding atoms only.
What is electronegativity? A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond.
What is a permanent dipole? A small charge difference across a bond that results from a difference in the electronegativities of the bonded atoms.
What is a polar covalent bond? A covalent bond with a permanent dipole.
What is a polar molecule? A molecule with an overall dipole, when you take into account any dipoles across the bonds.
What is an intermolecular force? An attractive force between neighbouring molecules.
What is a permanent dipole-dipole force? A weak attractive force between permanent dipoles in neighbouring polar molecules.
What are van der Waals' forces? Attractive forced between induced dipoles in neighbouring molecules.
What is a hydrogen bond? A strong dipole-dipole attraction between an electron deficient hydrogen atom on one molecule and a lone pair of electrons on a highly electronegative atom on a different molecule.
What is metallic bonding? The electrostatic attraction between positive metal ions and delocalised electrons.
What are delocalised electrons? Electrons that are shared between more than two atoms.
What is a giant metallic lattice? A three-dimensional structure of positive ions and delocalised electrons, bonded together by strong metallic bonds.
What is a simple molecular lattice? A three-dimensional structure of molecules, bonded together by weak intermolecular forces.
What is a giant covalent lattice? A three-dimensional structure of atoms, bonded together by strong covalent bonds.
What is a period? A horizontal row of elements in the Periodic Table. Elements show trends in properties across a period.
What is periodicity? A regular periodic variation of properties of elements with atomic number and position in the Periodic Table.
What is thermal decomposition? The breaking up of a chemical substance with heat into at least two chemical substances.
What is a displacement reaction? A reaction in which a more-reactive element displaces a less-reactive element from an aqueous solution of the latter's ions.
What is disproportionation? The oxidation and reduction of the same element in a redox reaction.
What is a precipitation reaction? The formation of a solid from a solution during a chemical reaction. Precipitates are often formed when two aqueous solutions are mixed together.
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