Download Worksheet 3 - contentextra

Worksheet 3.1
Chapter 3: Periodicity – glossary
Alkali An alkali is a base which is soluble in water. Examples of alkalis include Group 1 metal
hydroxides, Group 2 hydroxides and aqueous solution of ammonia, and amines.
Alkali metals The group of metals in Group 1. They react with water to produce hydrogen gas and
form strongly alkaline solutions.
Alkaline earth metals The group of metals in Group 2. They react with water to produce hydrogen
gas and a suspension of their hydroxide.
Alkaline solution
and a pH >7.
An alkaline solution is an aqueous solution that has an excess of hydroxide ions
Allotropy The ability of an element to exist in different crystalline forms or allotropes. Carbon, for
example, exists in the allotropic forms: graphite, diamond and fullerene.
Amphoteric
protons.
A substance which can behave both as an acid and a base, e.g. it can accept and donate
Amphoteric oxide An oxide of a metal that will react and dissolve in a solution of an acid and a
solution of a strong base (alkali). They can react as both acidic and basic oxides. Aluminum oxide is an
example.
Aqua-ions A complex ion with water molecules acting as ligands. Transition metals and aluminum
form aqua-ions in aqueous solutions.
Atomicity
The number of atoms in a molecule.
Atomic radius Half the distance of the closest approach of atoms in the crystal or molecule of a
chemical element (for a particular allotrope).
Base A substance which neutralizes an acid to produce a salt and water as the only products.
Common bases are aqueous ammonia, amines, carbonate ions and the oxides and hydroxides of metals.
A Brønsted–Lowry base is a proton acceptor; a Lewis base is an electron pair donor.
Basic oxide An ionic oxide, usually an oxide of a metal, that reacts with acids to form salts and
water. Soluble basic oxides react with water to form alkaline or basic solutions.
Bleach
A substance used to decolourize materials by a process of oxidation or reduction.
Charge density (of an ion) The ratio of the charge of an ion to its volume. The higher the charge
density of a positive ion, the greater its polarizing power. The higher charge density of a negative ion
the more difficult it is to be polarized.
1
Coordination number The number of ligands surrounding a central metal ion, or the number of
nearest neighbours an atom, molecule or ion has in a crystal structure.
Covalent radius of atom This is half of the inter-nuclear distance between two covalently bonded
atoms of the same element.
Dative covalent (coordinate) bond A dative covalent bond is formed when one of the atoms
supplies both electrons of the shared pair in a covalent bond.
Diatomic molecule Molecules composed of only two atoms, of either the same, X2, or different, XY,
chemical elements.
Dimer A molecule formed by the bonding of two identical monomers. The bonds will be relatively
strong hydrogen bonds or covalent bonds.
Dimerisation
The linking together of two molecules.
Displacement reaction A redox reaction in which a more reactive element displaces a less reactive
element from a solution of its ions or salt, often in aqueous solutions.
Disproportionation
The simultaneous oxidation and reduction of a single element.
Electrical conductivity A measure of the ability of a substance to conduct an electric current due to
the presence of mobile charged particles – either delocalized electrons in metals or graphite, or ions in
electrolytes.
Electronegativity A measure of the tendency of an atom in a molecule to attract a pair of shared
electrons towards itself. They are commonly measured on the Pauling scale which runs from 0.7 for the
least electronegative element, francium; to 4.0 for the most electronegative atom, fluorine. The
difference in electronegativities of two atoms in a covalent bond gives an indication of the bond’s
polarity.
Group A group is a vertical column of elements in the Periodic Table. The atoms of the elements in
the group all have the same number of electrons in their outer energy level, but a different number of
occupied energy levels.
Halide ions The halide ions are chloride (Cl–), fluoride (F–) bromide (Br–) and iodide (I–). The
halides are salts that contain a halide ion.
Halogens A group of non-metals in Group 7 of the Periodic Table. They exist as diatomic molecules
in their standard states.
Hydrolysis
A chemical reaction involving the reaction of water in which covalent bonds are broken.
Immiscible liquids
Liquids which do not mix (e.g. oil and water).
Ionic radius The radius of an ion in the crystalline form of a compound. Positive ions are smaller
than the corresponding atoms; negative ions are larger.
2
Ionization energy (first) The minimum energy required to remove one mole of electrons from a
mole of gaseous atoms to form a mole of univalent cations in the gaseous state. It is the enthalpy
change for the reaction: X(g) → X+(g) + e–.
Miscible liquids Liquids that mix in all proportions, for example, ethanol and water.
Monodentate ligand
A ligand that forms one dative covalent bond to a central metal ion.
Neutral solution An aqueous solution that has a pH of 7. It contains the same concentrations of
H+(aq) and OH–(aq) ions.
Noble gases A group of very unreactive gases found in Group 0 of the Periodic Table. They exist as
single atoms and have a stable s2p6 electron configuration. (Helium is an exception with a 1s2
configuration).
Non-metal Chemical elements that have typically low thermal and electrical conductivities. They
typically form covalent bonds and/or form negative ions (anions) and have acidic oxides.
Oxidation number A number given to indicate the degree of oxidation of an element. Fluorine
always has an oxidation number of –1 in its compounds. Oxygen has an oxidation number of –2 in its
oxides.
Oxide
–2.
A compound of oxygen with another element, where the oxygen has an oxidation number of
Oxy acid An acid in which the acidic proton is covalently bonded to an oxygen atom.
Period A period is a horizontal row of elements in the Periodic Table. Within a Period, the atoms of
the elements have the same number of occupied energy levels but an increasing number of electrons in
the outer energy level.
Periodicity The regular repetition of chemical and physical properties as you move across and down
the Periodic Table.
Periodic Table A table of the chemical elements arranged in order of increasing atomic number to
show the similar chemical properties of elements with similar electron configurations.
pH
pH = –log10 ([H+(aq)]).
Precipitate An insoluble substance produced by a chemical reaction in solution. It occurs when two
soluble salts react to give one soluble and one insoluble salt.
Resistance A measure of a component’s opposition to the flow of an electric current.
R (resistance) = V (potential difference ) /I (current in A ). It is measured in ohms (Ω).
Transition element/metal A set of metals in the Periodic Table, located between Groups 2 and 3,
which have incomplete d orbtital in their atoms or ions. Zn and Sc are not transition elements.
3
Trend A term used to describe the way in which a chemical or physical property increases or
decreases along a series of elements.
Universal indicator A mixture of indicators whose colour indicates the pH of an aqueous solution.
4