2012 topic 4.1 bonding - metallic

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  • Dear David
    I am glad that you find my chemistry resources useful. I must disagree with your statement of 'much taken from my Knockhardy Powerpoint' . I would say all, or most, wouldn't you!
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  • 1. IB Chemistry Power Points Topic 4 Bondingwww.pedagogics.ca LECTURE 3 Metallic Bonding
  • 2. METALLIC BONDING Involves a lattice of positive ions surrounded by delocalised electronsMetal atoms achieve stability by “off-loading” electrons to attain a morestable electron configuration.The free electrons are mobile and form a negative “cloud” which preventsthe newly-formed positive ions from flying apart.Atoms arrange in regular close packed The outer shell electrons of each atom 3-dimensional crystal lattices. leave to join a mobile “cloud” or “sea” of electrons which can roam throughout the metal. The electron cloud binds the newly- formed positive ions together.
  • 3. METALLIC PROPERTIES HIGH MELTING POINTSMelting point is a measure of how easy it is to separate individual particles.In metals it is a measure of how strong the electron cloud holds the + ions.The ease of separation of ions depends on the... ELECTRON DENSITY OF THE CLOUD IONIC / ATOMIC SIZE PERIODS Na (2,8,1) < Mg (2,8,2) < Al (2,8,3) m.pt 98°C 650°C 659°C b.pt 890°C 1110°C 2470°C + 2+ 3+ Na Mg Al MELTING POINT INCREASES ACROSS THE PERIOD THE ELECTRON CLOUD DENSITY INCREASES DUE TO THE GREATER NUMBER OF ELECTRONS DONATED PER ATOM. AS A RESULT THE IONS ARE HELD MORE STRONGLY.
  • 4. METALLIC PROPERTIES HIGH MELTING POINTSMelting point is a measure of how easy it is to separate individual particles.In metals it is a measure of how strong the electron cloud holds the + ions.The ease of separation of ions depends on the... ELECTRON DENSITY OF THE CLOUD IONIC / ATOMIC SIZE GROUPS Li (2,1) < Na (2,8,1) < K (2,8,8,1) m.pt 181°C 98°C 63°C b.pt 1313°C 890°C 774°C + + Li + Na K MELTING POINT DECREASES DOWN A GROUP IONIC RADIUS INCREASES DOWN THE GROUP. AS THE IONS GET BIGGER THE ELECTRON CLOUD BECOMES LESS EFFECTIVE HOLDING THEM TOGETHER SO THEY ARE EASIER TO SEPARATE.
  • 5. METALLIC PROPERTIES Metals are excellent conductors of electricityFor a substance to conduct electricity it must have mobile ions or electrons.Because the ELECTRON CLOUD IS MOBILE, electrons are free to movethroughout its structure. Electrons attracted to the positive end are replacedby those entering from the negative end. MOBILE ELECTRON CLOUD ALLOWS THE CONDUCTION OF ELECTRICITY
  • 6. METALLIC PROPERTIES Metals can have their shapes changed relatively easilyMALLEABLE CAN BE HAMMERED INTO SHEETSDUCTILE CAN BE DRAWN INTO RODS AND WIRESAs the metal is beaten into another shape the delocalised electroncloud continues to bind the “ions” together.Some metals, such as gold, can be hammered into sheets thinenough to be translucent.