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2016 topic 4.5 bonding - metallic

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IB Chemistry Bonding Topic 4

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2016 topic 4.5 bonding - metallic

  1. 1. LECTURE 3 Metallic Bonding IB Chemistry Power Points Topic 4 Bonding www.pedagogics.ca
  2. 2. METALLIC BONDING Involves a lattice of positive ions surrounded by delocalised electrons Metal atoms achieve stability by “off-loading” electrons to attain a more stable electron configuration. The free electrons are mobile and form a negative “cloud” which prevents the newly-formed positive ions from flying apart. Atoms arrange in regular close packed 3-dimensional crystal lattices. The outer shell electrons of each atom 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. 3. METALLIC PROPERTIES For a substance to conduct electricity it must have mobile ions or electrons. Because the ELECTRON CLOUD IS MOBILE, electrons are free to move throughout its structure. Electrons attracted to the positive end are replaced by those entering from the negative end. Metals are excellent conductors of electricity
  4. 4. METALLIC PROPERTIES MOBILE ELECTRON CLOUD ALLOWS THE CONDUCTION OF ELECTRICITY For a substance to conduct electricity it must have mobile ions or electrons. Because the ELECTRON CLOUD IS MOBILE, electrons are free to move throughout its structure. Electrons attracted to the positive end are replaced by those entering from the negative end. Metals are excellent conductors of electricity
  5. 5. MALLEABLE CAN BE HAMMERED INTO SHEETS DUCTILE CAN BE DRAWN INTO RODS AND WIRES As the metal is beaten into another shape the delocalised electron cloud continues to bind the “ions” together. Some metals, such as gold, can be hammered into sheets thin enough to be translucent. METALLIC PROPERTIES Metals can have their shapes changed relatively easily
  6. 6. The strength of metallic bonding depends on ELECTRON DENSITY (number of delocalized electrons) IONIC RADIUS CONSIDER GROUP 1 metals 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 STRENGTH of METALLIC BONDING MELTING POINT DECREASES DOWN A GROUP – bonds get weaker IONIC RADIUS INCREASES . . . Na + K + Li +
  7. 7. The strength of metallic bonding depends on ELECTRON DENSITY (number of delocalized electrons) IONIC RADIUS CONSIDER PERIOD 3 metals STRENGTH of METALLIC BONDING 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 Na + Al 3+ Mg 2+ MELTING POINT INCREASES ACROSS THE PERIOD THE ELECTRON CLOUD DENSITY INCREASES DUE TO THE GREATER NUMBER OF DELOCALIZED ELECTRONS. IONIC RADIUS DECREASES
  8. 8. ALLOYS An alloy is a mixture of different metals Alloys are specially designed for particular uses By manipulating the metal mix, physical properties can be enhanced such as: Greater strength Greater resistance to corrosion Enhanced magnetic properties Greater ductility Watch video and complete your notes

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