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Metallic, Ionic and Network Solids

Metallic, Ionic and Network Solids. SCH4U1 Mr . Dvorsky. Covalent Network Solids. Consist of atoms covalently bonded to each other in a continous pattern. Can be 2D or 3D. Has no natural beginning or end. e.g. Diamond, Graphite (allotropes of carbon)

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Metallic, Ionic and Network Solids

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  1. Metallic, Ionic and Network Solids SCH4U1 Mr. Dvorsky

  2. Covalent Network Solids • Consist of atoms covalently bonded to each other in a continous pattern. Can be 2D or 3D. • Has no natural beginning or end. • e.g. Diamond, Graphite (allotropes of carbon) -allotrope – one of two or more compounds consisting of the same element but having different physical properties. -can be more than one type of atom, e.g. SiO2

  3. Ionic Solids • Result from the reaction of a metal and a non-metal • Because of the large electronegativity difference, electrons transfer from the metallic atom to the non-metallic atom and the ions that result attract each other. • Thus ionic solids are held together by ionic bonds

  4. Ionic Solids -can be considered an array of positive and negative ions -arranged such that every positive ion has a negative neighbour and vice versa. -there are no distinct molecules in an ionic solid. -the attraction that the oppositely charged ions have for one another gives the solid its stability

  5. Ionic Solids • These solids are hard, have high melting points due to the strong ionic bonds. • Are brittle, and do not conduct electricity (no mobile electrons in them) • When they dissolve in water, they dissociate into ions and therefore form solutions which conduct electricity (in liquid state the ions and electrons are free to move).

  6. Ionic Solids • When comparing the properties of ionic solids we need to consider the strength of the ionic bond. • Strength of bond depends on: -1. atomic radii – the greater the distance between the ions = smaller force of attraction -2. the force of attraction between charged ions is proportional to the magnitude of charges on the ions (i.e. MgO has a higher melting point than NaCl because it has ions with greater charge on them)

  7. Ionic Solids

  8. Ionic solids are hard and brittle • Hammering can cause like charges to become aligned. –when this happens the crystal breaks along the line at which like charges are repelling each other.

  9. Metallic Solids • Metal atoms = low electronegativity, and valence shells that are less than half filled. • Therefore cannot attract or hold electrons of other atoms when they interact with others. • Instead, hold their own electrons so weakly that they pass from one atom to the next – are said to be delocalized.

  10. Metallic Solids • Electron sea model of metals – an ordered array of cations in a “sea” of freely moving electrons, with the positively charged ions attracted to many atoms of the electrons in the “sea” simultaneously.

  11. All pure metals except one are solids at room temperature – suggests that atoms are held rigidly in place. • Most form a uniform crystalline pattern • At microscopic level, can see that metals are made up of aggregates of millions of tiny crystals – from nanometres to several millimetres depending on the metal.

  12. Properties of Metals Melting/Boiling Points: -high mp and boiling point -requires a lot of kinetic energy to pull atoms away from adjacent molecules. -bp decreases down group 1 – have more orbitals, free valence electrons are further away, so strength of attractive force decreases. -mp increases left to right – more electrons in the sea, and larger charge of ion.

  13. Properties of Metals Malleability -can hammer some metals into shapes without breaking them. Gold is most malleable. -can hammer gram of gold into a sheet 1 metre squared and 230 atoms thick. -some malleable at room temp: copper, aluminum -iron must be heated to become malleable.

  14. Properties of Metals • Electrical and Thermal Conductivity of metals: are good conductors, since valence electrons free to move from atom to atom. • Same with heat conductivity – freely moving electrons receive kinetic energy from source of heat and pass it on to other electrons.

  15. Alloys • An alloy is a solid mixture of two or more different types of metal atoms • Addition of small amount of second metal with main metal can have big impact on properties. e.g. pure gold is too soft for dental crowns. The electron-sea model helps explain the structure of alloys. Interstitial versus substitutional

  16. Metallic Solids • Are able to absorb and re-emit light of all wavelengths – explains why they are shiny.

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