Metals and Ionic Compounds Flashcards
What is the metallic bonding model?
- Metals achieve stability by losing 1 or more valence electrons into a common pool within the lattice. The atom becomes a cation
- Positive ions are arranged in a closely packed structure which is regular, 3D network of positive ions. The cations occupy fixed positions in the lattice.
- Negatively charged electrons move freely thorough the lattice. These electrons are called delocalised electrons
- The positive cations are held in the lattice by the electrostatic forces of attraction between cations and delocalised electrons operating throughout the lattice.
Why are metals good conductors of electricity?
The delocalised electrons in a metallic lattice are free to move. If a source of electricity is applied across a metal electrons are forced in one end and are able to float out the other.
Why are metals good conductors of heat?
Delegalised electrons are able to bump into one another and the cations are able to transmit heat energy rapidly throughout the lattice.
Why are metals lustrous?
Delocalised electrons in the lattice reflect light of all wavelengths, metas appear shiny.
Define ductile and malleable
Ductile: able to be drawn into wires
Malleable: able to be beaten into sheets
Why are metals ductile and malleable?
-When beaten into sheets, drawn into wires or beat. layers of the positive ions are forced across each other. As this happens the delocalised electrons move so that they still surround positive ions. The electrostatic forces of attraction may change but still operate throughout the lattice.
Why do metals generally have high melting and boiling temperatures?
For most metals large amounts of heat energy is required to overcome the strong electrostatic force of attraction between cations and delocalised electrons.
What are the limitations in the metallic bonding model?
- range of meting points, hardness and densities of different metals
- differences in electrical conductivities of metals
- Magnetic nature of metals such as cobalt, iron and nickel
What is the structure of metal crystals?
A crystal is a region of a solid where the particles are arranged in a regular way. A sample of solid metal consists of many small crystals. Each crystal is a continuous regular arrangement of cations surrounded by a sea of delocalised electrons, but the arrangement of individual crystals with respect to one another is random.
How does the arrangement of crystals affect the way a metal behaves?
Generally, small crystals result in hard metals as there is less free movement of layers of cations over each other. Small crystals also have more areas of disruption between them, so the metal is more brittle.
-The larger the grains/crystals the larger the areas of perfect packing of cations. When beaten the cations easily move, the forces between them are adjusted and the lattice forms a flat sheet.
What are substitutional alloys?
Alloys made from elements of similar chemical properties and size.
-Because the different kinds of atoms are slightly different in size the layers within the lattice cannot move as easily past each other making the alloy harder and less malleable than pure metals.
What are interstitial alloys?
Interstitial alloys are where a small proportion of an element with a significantly smaller atom is added to a metal. The added atoms sit in interstices between metal cations in the metal lattice.
Are alloys compounds?
Alloys are not compounds because the elements are not chemically combined and there is no fixed ratio.
What are the properties of transition metals and what causes them?
Harder, higher densities and higher melting points.
This is because the atoms of transition metals are generally a small size due to greater core charger allowing them to pack together more tightly with stronger bonds.
Why do transition metal compounds display a wide range of colours?
The colours arise when electrons within the metal ion in the compounds absorb light of particular wavelets and move to higher energy levels. Absorbance of light with some wavelengths and transmission of light of other wavelengths results in the compound appearing coloured.
