Bonding (unit 1)

• Metallic bonding occurs between metal atoms, where the valence electrons are delocalized and free to move throughout the structure .
• Metallic bonding occurs between atoms of a metal
• Covalent bonding occurs between atoms of non-metals
• Ionic bonding occurs between atoms of non-metals and metals
• A compound is a material formed by chemically combining two or more elements
• In metallic bonding the outer electrons of the metal atom are free to move throughout the structure. The electrons are said to be delocalized. The positively charged nuclei of the atoms attract the electrons forming a metallic bond
• Metallic bonding can be described as: Positive ions in 'a sea' of delocalized electrons
• Metals often have relatively high melting and and boiling points. This is because a metallic bond is strong and requires a lot of energy to break it
• A metallic structure consists of a gigantic lattice of positively charged ions and delocalised outer electrons
• All metals regardless of state will conduct electricity. This is because they contain free electrons which will move and carry the current
• Metals are very insoluble in most solvents
• The attraction of the two positive nuclei for the shared pair of negative electrons forms the covalent bond
• The term molecule is used to describe a relatively small group of atoms held together by covalent bonds
• If a molecule has four bonds it probably has a tetrahedral shape
• If a molecule has three bonds it probably has a trigonal pyramidal shape
• If a molecule has two bonds its probably has a angular shape
• If a molecule has one bond it probably has a linear shape
• Simple Covalent (molecular): Covalent substances with low melting and boiling points and have a simple covalent structure. When these substances change state, only weak forces of attraction are broken not the strong covalent bonds this requires relatively small quantities of energy.
• Covalent Network (giant lattice): Covalent substances with high melting and boiling points and have covalent network structure. When these substances change state, the strong covalent bonds have to be broken requiring large quantities of energy
• Covalent network substances do not dissolve. Covalent substances (solids, liquids or gases) do not conduct electricity since they are made up of molecules which are uncharged and they do not have free electrons
• The attraction between oppositely charged ions is an ionic bond
• The structure of an ionic compound is known as a giant ionic lattice
• Ionic compounds have high melting and boiling points because strong ionic bonds must be broken in order to break up the lattice.
• Solid ionic compounds do not conduct electricity as they do not contain free ions or electrons. Many ionic compounds are soluble in water. When dissolved the ions move apart and can move freely. This means that ionic solutions will conduct electricity as the free moving ions can carry the charge.
• Sodium Chloride (NaCl) is known as table salt
• Ion: Charged particals that are formed when atoms lose or gain electrons.
• Compound: 2 or more different elements held together by chemical bonds. (N, H2O, CO2)
• Molecule: 2 or more atoms held together by chemical bonds. (H2O,CO2)