Simple particle theory is developed in this unit to include atomic structure and bonding. The arrangement of electrons in atoms can be used to explain what happens when elements react and how atoms join together to form different types of substances.
Substances that have simple molecular, giant ionic and giant covalent structures have very different properties.
Ionic, covalent and metallic bonds are strong.
However, intermolecular forces, the forces between molecules, are sometimes weaker, eg in carbon dioxide and iodine.
Metals have many uses. When different metals are combined, alloys are formed.
Shape memory alloys have a range of uses.
There are different types of polymers with different uses.
Nanomaterials have new properties because of their very small size.
Candidates should use their skills, knowledge and understanding to:
■ relate the properties of substances to their uses
■ suggest the type of structure of a substance given its properties
■ evaluate developments and applications of new materials, eg nanomaterials, fullerenes and shape memory materials.
Atomic structure and bonding - Definition of compound: Compounds are substances in which atoms of two or more elements are chemically combined. Quick reminder: the differences between atoms, elements, ions, compounds and mixtures (click here). Formation of a chemical bond between atoms: Chemical bonding involves either transferring or sharing electrons contained in the highest occupied energy levels of atoms in order to achieve the electronic structure of a noble gas (Group 0). ONLY Giant covalent macromolecules - Remember: Covalent bonds form between non-metal atoms. Each covalent represents a shared pair of electrons. Covalent bonds are very strong. There are two types of covalently bound molecule: simple molecules (click here) and giant covalent macromolecules. Carbon allotropes: graphite, diamond, amorphous carbon (soot, charcoal) and fullerenes are all examples of carbon allotropes. Allotropes are forms of an element that Ionic compounds - Structure Ionic compounds have regular structures (giant ionic lattices) in which there are strong electrostatic forces in all directions between oppositely charged ions. Examples of such crystals are the alkali metal halides (e.g. potassium chloride, sodium fluoride, sodium chloride) The exact arrangement of ions in an ionic lattice varies according to the size of the ions in the solid. Example NaCl Each Na+ Metallic structure and bonding - Metals form giant structures containing free electrons, making them good conductors of heat and electricity. Structure and properties Metals conduct heat and electricity because of the delocalised electrons in their structures. Conduction depends on the ability of electrons to move throughout the metal. The layers of atoms in metals are able to slide over each other and so metals can be bent and shaped. The strength Simple covalent molecules - Remember: Covalent bonds form between non-metal atoms. Each covalent represents a shared pair of electrons. Covalent bonds are very strong. There are two types of covalently bound molecule: simple molecules and giant covalent macromolecules (click here). Simple covalent molecules Simple molecular substances consist of molecules in which the atoms are joined by strong covalent bonds. Examples include the covalently bonded Polymer structure and intermolecular forces - LD and HD poly(ethene) The properties of polymers depend on what they are made from and the conditions under which they are made. For example, low density (LDPE) and high density (HDPE) poly(ethene) are produced using different catalysts and reaction conditions. LDPE HDPE branches on polymer molecules many few relative strength weak strong maximum usable temperature 85 ºC 120 ºC HDPE is more suited for Nanoscience - 1 nanometre = 1 x 10−9 m = 1,000,000,000 th of a metre = 1,000 millionth of a metre Nanoscience refers to structures that are 1–100nm in size, of the order of a few hundred atoms. The diameter of an atom is about 0.1nm Nanoparticles show different properties to the same materials in bulk and have a high surface area to volume ratio,
What are the relationships between atom, element, molecule, ion, compound and mixture? - What are the relationships between atom, element, molecule, ion, compound and mixture? Matter is made up of repeating units of atoms, molecules or ions. An element is a substance that contains only one type of atom as its repeating unit. A monatomic element has a single atom (e.g. copper, sodium or helium) repeating unit. Whereas, a polyatomic element, has a multiple atom C1.1 Atom ‘dot’ electron(s) and nucleus diagrams - Electrons occupy particular energy levels Each electron in an atom is at a particular energy level (in a particular shell). 1st shell (the ‘innermost’) shell can occupy a maximum of 2 electrons 2nd shell (‘outside the first shell’) can occupy a maximum of 8 electrons 3rd shell (‘outside the second shell’) can occupy a maximum of 8 electrons At GCSE level, because C1.1 Atoms - The difference between atoms, elements, compounds, mixtures and ions always confuses students. Further information may be found here. Atom All substances are made of tiny particles called atoms. Atoms have a small central nucleus, which is made up of protons and neutrons and around which there are electrons. Element A substance that is made of only one sort of atom
Chemical bonding simulation by Kent Chemistry (click here)
BP Heating substances and changing states of matter video