分类物质

WordDefinitionTopicallotropesAllotropes are structurally-different forms of an element. They differ in the way the atoms bond with each other and arrange themselves into a structure. Because of their different structures, allotropes have different physical and chemical propertiesClassifying materialsatomAll elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons.Classifying materialscompoundA compound is a substance formed by the chemical union (involving bond formation) of two or more elements.Classifying materialsconductTo allow electricity, heat or other energy forms to pass through.Classifying materialscovalent bondA covalent bond between atoms forms when atoms share electrons to achieve a full outer shell of electrons.Classifying materialsdouble bondA double bond is a covalent bond resulting from the sharing of four electrons (two pairs) between two atoms.Classifying materialsductileIf a material is ductile it is capable of being drawn into thin sheets or wires without breaking.Classifying materialselectronAn electron is a very small negatively-charged particle found in an atom in the space surrounding the nucleus.Classifying materialselectrostaticAn electrostatic force is generated by differences in electric charge (ie positive and negative) between two particles. It can also refer to electricity at rest.Classifying materialsformulaA formula is a combination of symbols that indicates the chemical composition of a substance.Classifying materialsgroupsThe groups of elements in the periodic table are the elements which have the same number of electrons in their outer shells and so have similar chemical properties. A group of elements all lie in same column in the periodic table.Classifying materialsionAn ion is a charged particle formed by loss or gain of electrons. When atoms lose an electron they become a positive ion. When they gain an electron they become a negative ion.Classifying materialsionsCharged particles formed by loss or gain of electrons. When atoms lose an electron they become a positive ion. When they gain an electron they become a negative ion.Classifying materialsionic bondAn ionic bond forms between two atoms when an electron is transferred from one atom to the other, forming a positive-negative ion pair.Classifying materialsionic compoundAn ionic compound occurs when a negative ion (an atom that has gained an electron) joins with a positive ion (an atom that has lost an electron): The ions swap electrons to achieve a full outer shell.Classifying materialsisotopesAtoms of the same element that have different numbers of neutrons are called isotopes.Classifying materialslatticeA lattice is a regular grid-like arrangement of atoms in a material.Classifying materialslubricantA substance used to reduce the friction between two solid surfaces.Classifying materialsmalleableIf a material is malleable it is capable of being hammered or pressed out of shape without being likely to break or return to the original shape.Classifying materialsmassMass is a measure of the amount of material in an object. It is measured in grams (g).Classifying materialsmass numberThe mass number (A) of an element is the number of protons plus the number of neutrons in the nucleus of the atom.Classifying materialsmolecular compoundA molecular compound is made up of at least two different elements, which share electrons to form covalent bonds.Classifying materialsmoleculeA molecule is a collection of two or more atoms held together by chemical bonds. It is the smallest part of a substance that displays the properties of the substance.Classifying materialsmoltenMolten means reduced to liquid form by heating. It is mainly used to describe rock, glass or metal.Classifying materialsnegligibleSo small as to be not worth considering.Classifying materialsnucleusFound at the centre of an atom, the nucleus contains protons and neutrons.Classifying materialsneutronA neutron is a particle that is found in the nucleus of an atom, has a mass approximately equal to that of a proton, and has no electric charge.Classifying materialsproductA product is a substance formed in a chemical reaction.Classifying materialsprotonsA proton is a small particle with a positive charge found in the nucleus of the atom.Classifying materialsradioactiveA radioactive isotope gives off (or is capable of giving off) radiant energy in the form of particles or rays by the spontaneous disintegration of the nucleus.Classifying materialsreactantA reactant is a substance put together with another substance/substances to undergo a chemical reaction.Classifying materialsrelative massThe relative mass is the number of times heavier a particle is, compared to another.Classifying materialsstableAtoms are stable if their outer shell contains its maximum number of electrons.Classifying materials