chemical bonding and the lewis structure
TRANSCRIPT
Metallic
Bonds
Metal + Metal
Covalent BondsNon-Metal + Non-Metal
Electrons are shared
between atoms.
Ionic Bond
sMetal +
Non-Metal
Electrons are
transferred.
Valence electrons• Electrons in the outer energy level of atom.• Are involved in chemical bonding.• Are easily removed.
Noble gases obey the octet structure.
•Forms molecules.•Molecule is held together by a shared electron pair.• Individual atoms in the molecule has octet structure.
Metals give off electrons to form cations in order to obtain a noble gas electron structure.
Li Li+ + e-[He]2s1 [He]
[Ar]4s2 [Ar]Ca Ca2++2e-
Non-metals gain electrons to form anions in order to obtain a noble gas electron structure.
N + 3e- [ N ]3-[He]2s2p3
S + 2e- [ S ]2-[Ne]3s23p4
[He]2s22p6 = [Ne]
[Ne]3s23p6 = [Ar]
• The metal atom gives away its electrons to the non-metal.
• The positive and negative ions attract each other due to electrostatic forces.
(opposite charges attract)• The electrostatic attraction is the ionic
bond.• Crystal lattices form, and are built up of
alternating positive and negative ions.
Ca Ca2+ + 2e-
2x: F + e- [ F ]-
Ca2+ + 2[ F ]- Ca2+2[ F ]- CaF2
Positive ion:
Negative ion:
Crystal lattice
Ionic compounds are in fact composed of many millions of ions, and not just one cation and one anion. This huge structure is known as a crystal lattice.
NaCl is the FORMULA unit (not a molecule of salt.)
Electrostatic attraction between the positive
atomic residue and the sea of delocalised
electrons. Metallic bonds
• Atoms have 1, 2, or 3 valence electrons.• Metallic atoms have a low ionisation energy.• Little energy required to remove valence
electrons – electrons delocalise.• Atoms are tightly packed to form a metal
lattice where the valence orbital overlap.• Atoms that lose an electron becomes positive
(called a positive atomic residue).• The bonding energy is the electrostatic force of
attraction between the sea of delocalised electrons, and the positive atomic residue.
Properties of metals
Reason
Metal glow Sea of delocalised electrons can reflect light and therefore causes the surface to shine.
Electrical conductor Sea of delocalised electrons can move freely and act as charge carriers.
Thermal conductor Sea of delocalised electrons act as carriers of heat energy (kinetic energy).
Malleable/Ductile Atoms, though firmly bound together, can slide over each other, allowing metal to bend and
stretch.High density Atoms in the solid phase is packed closely
together in a metal lattice.
Metals are often converted into alloys to change their
properties. Alloys are usually always stronger than pure
metals.
Text: Olivier, A: Physical Science textbook and workbook, Grade 10 ; Reivilo Uitgewers.Slide 8 – 11: Lily KotzèSlide 18: Lily KotzèSlide 20: http://dtc-wsuv.org/isci/module/img/7_14_NaCl.png Slide 24: http://i.imgur.com/oIoEZhH.gif Slide 27: http://i0.wp.com/upload.wikimedia.org/wikipedia/commons/thumb/3/36/Alloy_Substitutional.svg/150px-Alloy_Substitutional.svg.png?w=625Slide 28: Steel: https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcRb7xMBVsBuBLTvAOfjtLXoghcMRgMkIH5puPfnzKRRKmwUNtHk Stainless steel: http://curiousscience.com/images/stock/img780.jpg Bronze: https://upload.wikimedia.org/wikipedia/commons/c/ca/Apa_Schwerter.jpg