Comparing models
Different A description of how a chemical bond is formed and/or the structure produced by the atoms. Bonding models can often be used to explain the properties of a substance. represent the structure and bonding present in substances. Each have certain features and limitations. For example, the model of the metallic A regular grid-like arrangement of atoms in a material. does not show more than one layer of metal Electrically charged particle, formed when an atom or molecule gains or loses electrons., or that the Electrons that are not associated with a particular atom, eg in a metal, outer electrons can be free to move through the solid. Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. are in constant motion.
Models for ionic compounds
An 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). form a regular lattice structure in which oppositely charged ions are strongly attracted to each other. Sodium chloride is an ionic compound. The table shows some limitations of different models for sodium chloride.
Models for simple molecular substances
The The smallest part of an element that can exist. in a simple Refers to a substance made up of molecules, so it contains small groups of atoms, of a set size, held together by covalent bonds. substance are joined together by strong A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons.. A collection of two or more atoms held together by chemical bonds. are attracted to each other by weak Weak attractive forces between molecules. When a simple molecular substance melts or boils, it is the intermolecular forces that are broken (not the covalent bonds in each molecule).. Water is a simple molecular substance. The table shows some limitations of different models of water: