CHAPTER 4: METALLIC BONDING Flashcards
metallic properties (9)
- exhibit a range of melting points and relatively high boiling points
- good conductors of electricity
- good conductors of heat
- generally have high densities
- are malleable → can be shaped by beating or rolling
- are ductile → can be drawn into a wire
- are lustrous or reflective when first cut or polished
- are often hard with TENSILE strength → can resist a pulling force
- have low ionisation energies and electronegativities
alkali metals
- soft enough to be cut with a knife
- react VIGOROUSLY with water to produce hydrogen gas
forming metal ions
metal ions tend to lose their valence electrons to form positive ions called cations (octet rule → 8 electrons in valence shell)
properties of transition metals
- tend to be harder and stronger
- have higher densities
- have higher melting points and boiling points
- some have strong magnetic properties
- high tensile strength
- atoms of transition metals generally have a smaller size because of their greater core charge
- allows them to pack together more tightly with stronger bonds
- gives transition metals their properties
- transition metal compounds display a wide range of different colours
- exception: mercury is a liquid at room temperature
- it can be called the noble gas of metals
metallic bonding model
- positive ions are arranged in a lattice structure and occupy fixed positions
- negatively charged electrons move freely throughout the lattice
- these electrons are called delocalised electrons because they belong to the lattice as a whole, rather than staying in the shell of a particular atom
- delocalised electrons come from the outer shells of the atoms
- inner shell electrons are NOT free to move throughout the lattice and remain firmly bonded to the individual cations
- the positive cations are held in the lattice by the electrostatic force of attraction between these cations and the sea of delocalised elections
- this attraction is known as the metallic bonding model
explaining property: ‘metals are hard and have relative high boiling points’
strong electrostatic forces of attraction between positive metal ions and the sea of delocalised electrons holds the metallic lattice together
explaining property: ‘metals are good conductors of electricity’
free moving delocalised electrons will move towards a positive electrode and away from a negative electrode in an electric circuit
explaining property: ‘metals are malleable and ductile’
when a force causes metal ions to move past each other, layers of ions are still held together by the delocalised electrons between them
explaining property: ‘metals generally have a high density’
- cations in a metal lattice are closely packed
- the density of a metal depends on the mass of the metal ions, their radius, and the way in which they are packed
explaining property: ‘metals are good conductors of heat’
when the delocalised electrons bump into each other, and into the metal ions, they transfer energy to their neighbours
explaining property: ‘metals are lustrous’
because of the presence of free electrons in the lattice, metals reflect light of all wavelengths and appear shiny
limitations of the metallic bonding model
- range of melting points, hardness and densities of different metals
- differences in electrical conductivities of metals
- magnetic nature of metals such as cobalt. iron and nickel
reactivity of metals with water
- metals in group 1 are more reactive in water than those in group 2
- going down a group, the reactivity of the metal in water increases
- transition metals are generally less reactive with water than group 1 and group 2 metals are
- metal + water → metal hydroxide + hydrogen gas
eg. 2Na + 2H2O → 2NaOH + 2H2
reactivity of metals with acids
- the reactivity of different metals with acids follows the same general pattern as the reactivity of metals with water
- metals are normally more reactive with acids than with water
- metal + hydrogen chloride (HCl) -> metal chloride + hydrogen gas
eg. Mg + 2HCl -> MgCl2 + H2
reactivity of metals with oxygen
- the group 1 metal all react rapidly with oxygens
- the group 2 metals also react with oxygen to form oxides → not as rapidly as group 1 metals
- heat is usually required to start the reaction
- the transition metals are less reactive with oxygen than the metals in group 1 and group 2
- metal + oxygen gas (O2) → metal oxide
eg. 4K + O2 → 2K2O
