Introduction to Chemistry – Background for Nanoscience and Nanotechnology Prof. Petr Vanysek

Introduction to Chemistry: Compounds

Chemical Bonding Covalent bonds Ionic bonds Metal bonding

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.

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.

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.

Covalent and Ionic Bonding Atom# of Covalent BondsTypical charge for an Ion H1+1 C4 O2-2 N3 F, Cl, Br, I1 S2-2 Si4 Li, Na, K+1 Be, Mg, Ca, Sr, Ba+2

Polar Molecules –If the electron density is not distributed evenly around a molecule then they are polar.

Intermolecular Bonding Bonding 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.

Hydrogen Bonding H O H

O H H O H H

Dipole Interaction The partial positive and negative ends of the molecules hold the molecules together.

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.

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. CC HH HH ) ( n nCH 2 =CH 2

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.

Structure of Materials Grains Crystals Crystal Unit Cell Electron orbitals Atom

Biological Organization Tissue Cells Organelles Proteins Nucleic Acids Membranes

Review of Chemistry States of Matter Atoms, Molecules and Ions Subatomic particles Periodic Table Covalent and ionic bonding Chemical reactions Intra-molecular forces Polymers