Introduction to Chemistry – Background for Nanoscience and Nanotechnology
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Transcript of Introduction to Chemistry – Background for Nanoscience and Nanotechnology
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Introduction to Chemistry – Background for Nanoscience and Nanotechnology
Prof. Petr Vanysek
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Introduction to Chemistry:
Compounds
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Chemical Bonding
• Covalent bonds• Ionic bonds• Metal bonding
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Covalent bonds
• Covalent bonding is when electrons are shared between to atoms or more.
• The number of covalent bonds an atom is likely to form is determined by its place in the periodic table and the number of valence electrons it has.
• An atom will share electrons with another atom so that it results in them both having a full valence shell. Usually this will be 8 electrons.
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Ionic bonds
• When a metal and a non-metal form bonds they are typically ionic bonds where electrons are transferred from the metal to the non-metal.
• Some metals will lose enough electrons to achieve a complete valence shell.
• Non-metals will usually gain enough electrons to achieve a complete valence shell.
• Many metals are able to form ions with more than one charge.
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Metal bonding
• In metals the atoms are held together by metal bonding. Electrons can easily transfer from one atom to the next. This suggests a model of positive ions in a sea of electrons. Metals can conduct electricity because electrons flow easily in any direction.
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Covalent and Ionic BondingAtom # of Covalent Bonds Typical charge for an
Ion
H 1 +1
C 4
O 2 -2
N 3
F, Cl, Br, I 1 -1
S 2 -2
Si 4
Li, Na, K +1
Be, Mg, Ca, Sr, Ba +2
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Polar Molecules
• Polar Molecules– If the electron density is not distributed evenly
around a molecule then they are polar.
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Intermolecular BondingBonding between molecules
van der Waals forces• Hydrogen bonding
– This relatively strong type of inter-molecular bonding which typically occurs between a hydrogen atom of one molecule and an electron pair or electronegative atom of another molecule.
– Multiple hydrogen bonds hold the DNA double helix together.
• Dipole interaction• London forces
– These are induced forces caused by a temporary rearrangement of the electron clouds when molecules bump together.
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Hydrogen Bonding
+
--+
H
OH
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Hydrogen Bonding
OH
H
OH
H
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Dipole Interaction
• http://www.chemguide.co.uk/atoms/bonding/vdw.html
• The partial positive and negative ends of the molecules hold the molecules together.
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London Forces
Two hexane molecules approach.
The hexane molecules bump into each other.
The electron clouds rearrange to form a temporary dipole.
+ + +- - -
+ + +
- - -
London forces are induced dipoles caused by temporary rearrangement of the electron cloud.
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Polymers
• Polymers are large chainlike molecules that are built from smaller molecules called monomers.
• For example polyethylene is formed from ethylene:
• Proteins are natural polymers.
• http://www.pslc.ws/macrog.htm
C C
H H
H H
)(n
nCH2=CH2
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Chemical Reactions
• Involve the making or breaking of chemical bonds.
• Chemical reactions result in making a new substance with different properties from the original substance.
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Structure of Materials
Grains Crystals Crystal
Unit CellElectron orbitalsAtom
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Biological Organization
Tissue Cells Organelles
Proteins Nucleic AcidsMembranes
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Review of Chemistry
• States of Matter• Atoms, Molecules and Ions• Subatomic particles• Periodic Table• Covalent and ionic bonding• Chemical reactions• Intra-molecular forces• Polymers