Chemistry Notes Introduction to Chemical Bonding Introduction Chemical reactions involve the making and breaking of bonds It is essential that we know what bonds are before we can understand any chemical reaction To understand bonds we will first describe several of their properties The bond strength tells us how hard it is to break a bond Bond lengths give us valuable structural information about the positions of the atomic nuclei Bond dipoles inform us about the electron distribution around the two bonded atoms From bond dipoles we may derive electronegativity data useful for predicting the bond dipoles of bonds that may have never been made before From these properties of bonds we will see that there are two fundamental types of bonds covalent and ionic Covalent bonding represents a situation of about equal sharing of the electrons between nuclei in the bond Covalent bonds are formed between atoms of approximately equal electronegativity Because each atom has near equal pull for the electrons in the bond the electrons are not completely transferred from one atom to another When the difference in electronegativity between the two atoms in a bond is large the more electronegative atom can strip an electron off of the less electronegative one to form a negatively charged anion and a positively charged cation The two ions are held together in an ionic bond because the oppositely charged ions attract each other as described by Coulomb s Law Ionic compounds when in the solid state can be described as ionic lattices whose shapes are dictated by the need to place oppositely charged ions close to each other and similarly charged ions as far apart as possible Though there is some structural diversity in ionic compounds covalent compounds present us with a world of structural possibilities From simple linear molecules like H2 to complex chains of atoms like butane CH3CH2CH2CH3 covalent molecules can take on many shapes To help decide which shape a polyatomic molecule might prefer we will use Valence Shell Electron Pair Repulsion theory VSEPR VSEPR states that electrons like to stay as far away from one another as possible to provide the lowest energy i e most stable structure for any bonding arrangement In this way VSEPR is a powerful tool for predicting the geometries of covalent molecules Terms Anion A negatively charged ion Bond That which holds together atoms in molecules and ions in lattices Cation A positively charged ion Coulomb s Law A mathematical formula whose consequence is that negatively and positively charged particles attract each other and similarly charged species repel each other Covalent Bond A bond that results from a sharing of electrons between nuclei Ion A charged species created by the gain or loss of an electron from an atom or neutral molecule Ionic Bond A bond that results from electrostatic attraction between oppositely charged ions The cation is positively charged while the anion is negatively charged Lattice A regularly repeating three dimensional array of atoms molecules or ions Molecular Orbital A combination of atomic orbitals in molecular orbital theory that provides an orbital description of a molecule analogous to the atomic orbital description of atoms Molecular Orbital Theory A description of bonding that combines atomic orbitals from each bondedatom to produce a set of molecular orbitals Molecule A chemical species containing a covalent bond Valence Shell Electron Pair Repulsion Theory A theory used to predict bonding geometries that states that electron pairs will be distributed about the central atom to minimize electron pair repulsions