Metallic, Ionic and Network Solids

SCH4U1Mr. 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)-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

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

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

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).

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)

Ionic Solids

• 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.

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.

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.

• 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.

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.

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.

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.

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

Metallic Solids

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