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Danyal Education (Contact: 9855 9224) “A commitment to teach and nurture” The Particulate Nature of Matter: Structure and Properties of Materials Candidates should be able to: a) Describe the differences between elements, compounds and mixtures on b) Compare the structure of simple molecular substances, eg methane; iodine, with those of giant molecular substances, eg poly(ethene); sand (silicon dioxide); diamond; graphite in order to deduce their properties (*) (#) al Ed uc ati c) Compare the bonding and structures of diamond and graphite in order to deduce their properties such as electrical conductivity, lubricating or cutting action (candidates will not be required to draw the structures) (*) (#) Da ny d) Deduce the physical and chemical properties of substances from their structures and bonding and vice versa (*) (#) * not in combined Science syllabus # not in N level Science syllabus O Level Chemistry – Structure and Properties of Materials 1 Danyal Education (Contact: 9855 9224) “A commitment to teach and nurture” What is an atom? What is an element? An atom is the smallest particle of an element that has the chemical properties of that element. An element is a pure substance that cannot be split into 2 or more simpler substances. (Eg, N, O, Mg, Ca) What is a compound? (A mono-atomic element is a non-metal element that exists as atoms. Eg all noble gases like Ne, Ar) What is a mixture? on A compound is a pure substance that contains two or more elements chemically combined. (Eg MgO, NaCl, NH4NO3) A mixture is made up of two or more substances added together without chemical bonds being formed. (Eg air, crude oil, sugar solution) What is a molecule? al Ed uc ati A molecule is a pure substance that contains two or more non-metal atoms that are chemically combined. (Molecules formed by the combination of two atoms are called di-atomic molecules, eg O2, N2, Cl2, CO. Molecules consisting of three atoms are called triatomic molecules, eg O3, CO2. Molecules consisting of four or more atoms are called polyatomic molecules, eg P4, S8, NH3) What are the differences between a mixture and a compound? S.P.E.C. Properties No chemical reaction takes place when a A chemical reaction takes place when a mixture is formed – usually there is little compound is formed – usually there is an or no energy change. energy change. Da Energy Change Mixture Compound The components of a mixture can be The elements in a compound can only be separated by physical methods. separated by chemical methods or electricity. The chemical properties of a mixture are The physical and chemical properties of a the same as those of its components. compound are different from those of the elements in the compound. ny Separation Composition The components of a mixture can be The elements in a compound are always mixed in any proportion. combined in a fixed proportion by mass. O Level Chemistry – Structure and Properties of Materials 2 Danyal Education (Contact: 9855 9224) “A commitment to teach and nurture” Describe the structure of a simple molecular structure. Give 3 examples of substances with this type of structure. al Ed uc ati on In a simple molecular structure, the molecules exist as simple, discrete molecules. Within each molecule, the elements are held together by strong covalent bonds. Between molecules, weak intermolecular forces of attraction hold the molecules together. Eg iodine, methane, carbon dioxide, water Describe the structure of a giant molecular structure. Give 3 examples of substances with this type of structure. In a giant molecular structure, a large number of atoms are joined together by strong covalent bonds, forming a giant network of atoms. Eg diamond, graphite, silicon(IV) oxide, silicon carbide Da ny (Both diamond and graphite are allotropes of carbon. Allotropes are different forms of the same element.) O Level Chemistry – Structure and Properties of Materials 3 Danyal Education (Contact: 9855 9224) “A commitment to teach and nurture” Physical Properties of Substances with Simple Molecular Structure Physical Property Explaination using structure Low melting point and boiling point High volatility Weak inter-molecular forces of attraction Very little energy is required to overcome these forces Usually liquids or gases at r.t.p. No free moving ions or electrons to transfer electric charges Usually insoluble in water Do not dissociate completely into its ions in water on Do not conduct electricity in any state al Ed uc ati Usually soluble in organic solvents Physical Properties of Substances with Giant Molecular Structure Physical Property Explanation using structure High melting point and boiling point Non-volatile Solids at r.t.p. Strong covalent bonds between atoms All the atoms are joined together to form a giant network of atoms A lot of energy is required to break these strong covalent bonds Do not conduct electricity in any state (except graphite) No free moving ions or electrons to transfer electric charges (except for graphite, which has delocalized, mobile electrons) Insoluble in all solvents Do not dissociate into its ions in all solvents Comparing the Structures and Bonding of Diamond and Graphite Diamond Each carbon atom is joined to four other carbon atoms by strong covalent bonds in a tetrahedral arrangement. ny Da Giant Molecular Structure Properties Uses Graphite Within each layer, each carbon atom is joined to three other carbon atoms by strong covalent bonds. Layers of carbon atoms lie on top of each other, held together by weak forces of attraction. Hard Very high melting and boiling points Non-conductor of electricity Soft Very high melting and boiling points Conductor of electricity As gemstones As tips of cutting, grinding and polishing tools In pencils As a dry lubricant As inert electrodes O Level Chemistry – Structure and Properties of Materials 4