Properties of Substances Describe the types of bonding covered so far. Describe the properties that are generally exhibited by substances because of the bonding present Compare and contrast properties to evaluate the type of bonding a substance will have.

Properties of Substances Copy the following into your jotter and write below the table A to F and next to each letter write down the bonding it is most likely to have considering its properties: A) Discrete Covalent B) Metallic C) Covalent network D) Ionic F) Covalent molecule E) A cheeky wee metal

Types of bonding ionic bonding – electrons are transferred from metal to non-metal atoms form positive and negative ions. These oppositely-charged ions are attracted to each other. In a giant lattice of oppositely charged ions [electrostatic attraction] covalent bonding – electrons are shared between non-metal atoms. Two kinds discrete covalent bonding i.e. NH3 or CO2 strong bonds in the molecule [intra-molecular bonding] and weak forces of attraction between molecules [intermolecular bonding metallic bonding – electrons become delocalized and form a sea of free electrons, which attracts positive metal ions.

Melting and boiling point: giant structures Substances with giant structures generally have high melting and boiling points because all the atoms are strongly bonded together to form a continuous 3D lattice or structure. A large amount of energy is needed to break these bonds. strong covalent bonds holds atoms together + - strong metallic bonds holds ions together strong ionic bonds holds ions together

Melting and boiling point: molecules Simple molecular substances have low melting and boiling points because the forces that hold the molecules together are weak and easily broken. weak bonds between molecules strong bonds within molecules In general, the larger the molecule, the higher the melting and boiling point.

Images of the types of bonding

Ionic lattices and crystals The structure of the lattice means that the ionic compound forms a crystal. This has flat sides and straight edges. These are crystals of sodium chloride. Acknowledgement The image is a coloured scanning electron micrograph (SEM) of  common salt,  sodium chloride,  recrystallised from distilled water.  The salt crystal  is  built up  from  a cubic  lattice  of sodium and chloride ions.  In the  absence  of  impurities  the  exact cubic  crystal form is  produced.  This micrograph shows that in practice this basic cube is  usually disrupted  by  dislocations;   these  give rise to crystals with a variety of shapes,  although  they all    retain    the    basic    cubic   symmetry. Magnification: x280 at 5x7cm size. x975 at 10x8‘. Credit: Andrew Syred/Science Photo Library All ionic compounds form lattices and crystals when solid.

Covalent network

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Predicting bonding

True or false?

Conductivity Experiment

Conductivity – ionic substances Ionic substances cannot conduct electricity when solid because the ions are bonded together in the lattice. + - ions cannot move to carry a charge When liquid (molten) or dissolved, however, the ions are able to break free of the lattice. + - ions are able to move and carry a charge

Conductivity – covalent substances Substances with covalent bonding do not conduct electricity because all the outer electrons are fixed in shells. electrons unable to move and carry a charge The exception is graphite, which has free electrons between layers of carbon atoms.

Conductivity – metals Metals can conduct electricity because the sea of delocalized electrons between the metal ions are free to move anywhere in the structure. sea of electrons metal ions electrons free to move and carry an electrical charge

Bonding and electrical conductivity

Solubility Substances with giant covalent or metallic structures generally do not dissolve easily in water or other solvents. This is because dissolving involves breaking bonds, which needs lots of energy. Many ionic substances dissolve in water because water molecules have a slight electrical charge and can attract the ions away from the lattice. Simple molecular substances are usually insoluble in water but soluble in solvents such as petrol.

Strength Substances with giant structures are generally hard because a large amount of energy is needed to break ionic, covalent and metallic bonds. Ionic substances are hard but brittle – when a force is applied, ions with like-charges are brought together. These repulse each other and cause the lattice to shatter. Covalent substances are hard but brittle – the covalent bonds do not bend but break when enough force is applied. Graphite is slippery because the weak forces between layers of carbon atoms can easily be broken. Metals are hard but malleable and ductile – the delocalized electrons allow the metallic bonds to move.

Ionic lattices + - - + - - - + + + - + + - - - - + + + - - - + + + - - In an ionic compound, millions and millions of ions are packed together in a regular cubic arrangement, joined by ionic bonds. This forms a giant 3D structure called an ionic lattice. + - - + - - - + + + - + + - - - - + + + - - - + + + - - - + + + - - - + + +

Strength of ionic compounds Ionic compounds are brittle – they shatter when they are hit. force + - + - + - repulsion + - When the lattice is hit, a layer of ions is shifted so that ions with the same charges are lined up together. These like charges repel each other, thereby splitting the lattice.

Density The density of a substance depends on the type and strength of bonding and how the atoms/ions are arranged. Giant substances, especially metals, are dense because the atoms/ions are tightly packed together. strong bonds cause tight packing Substances with simple molecular structures have lower densities. The weak forces between molecules cannot pull the molecules together tightly. weak bonds cause loose packing

True or false?

Effect of structure on properties

Glossary  covalent bond – A strong bond between two atoms in which each atom shares one or more electrons with the other.  delocalized – Electrons that are free to move throughout a structure. In metals, they form a ‘sea of electrons’.  ionic bond – The strong electrostatic force of attraction between oppositely charged ions.  giant structure – A structure containing millions of atoms or ions bonded together. The structure extends in three dimensions until all available atoms or ions are used up.  lattice – A 3D structure of closely packed atoms or ions.  metallic bonding – The strong attraction between positive metal ions and a sea of electrons.  molecule – A simple structure containing two or more atoms covalently bonded together.

Anagrams

The effect of bonding on properties

Comparing bonding – team game

Multiple-choice quiz