Chemical Bonding Flashcards
Covalent bonds
Occur between elements – usually nonmetals – that have a difference in electronegativity between zero and 1.7.
In covalent bonds, electrons are shared between two atom. The attraction is created from the attraction between opposite magnetic fields created by the two electrons in the bond. The number of covalent bonds that a nonmetal may form equals eight minus the group number of the element.
Ionic attractions
Occur between elements – usually combination of metal and nonmetal atoms – that have a difference in electronegativity greater than or equal to 1.7.
In an ionic attraction, an electron leaves the less electronegative atom – creating a positive charge, and migrates to the more electronegative atom – creating a negative charge. The unlike charges that result create an attraction between the two atoms.
Ionic attraction follows Coulomb’s Law. The strength of attraction is directly proportional to the amount of charge and inversely proportional to the square of the distance between the two charges.
Ionic attractions satisfy the valence shells of the elements involved in the attraction. The metal loses electrons to have a filled shell. The nonmetal gains electrons to have a filled shell.
Double and triple bonds
Electrons in a covalent bond satisfy the valence shell octets of both elements in the bond. The first covalent bond between two nonmetals is a sigma bond(σ), where the electrons are paired along the axis between the two atoms. Any additional covalent bonds between nonmetals are pi bonds(π), where the electrons are paired through the sideways overlap of P- orbitals above and below the inter-nuclear axis. For example, a double bond consists of one sigma and one pi bond. Sigma bonds are much stronger than pi bonds, and are therefore more difficult to break.
Nonpolar covalent bonds
They form when the difference in electronegativity of the two atoms is negligible (<0.4). Electrons in the bond are shared equally. Typical examples of nonpolar bonds are those between diatomic molecules of the same element(F2, Cl2, O2).
Polar covalent bonds
They form when the difference in electronegativity of the two atoms is between 0.4 and 1.7. In a polar covalent bond, the element with the greater electronegativity takes on a slightly negative charge, and the element with the lesser electronegativity takes on a slightly positive charge. In effect, the electrons in the bond are closer to the element with the greater electronegativity.
Dipole moment
A dipole moment exists in a polar covalent bond that points to the more electronegative atom. Dipole moments add together like vectors to create a total dipole moment on the molecule.
Network covalent
Network covalent crystals are groups of nonmetal atoms held together by covalent bonds. A commonly cited example is a diamond, which is a network covalent crystal of carbon atoms.
Network covalent crystals tend to have very high melting and boiling point, and a very high amount of energy is needed to break apart the Crystal.
Metallic attraction
Outer electrons of metals are delocalized (shared between multiple bonds) and may be associated with one atom or another.
Delocalized electrons give metals many of their physical properties: luster (because easily excited electrons give off photons as they return to the ground state), and electrical and thermal conductivity (because electrons move easily from atom to atom).
Metallic bonding is created because all the metallic atoms share their outer electrons in a manner that is thought of as an “electron sea.” The electrons, which are delocalized, move freely between the outer energy levels of the different atoms. This delocalization of electrons promotes electrical and thermal conductivity. Metals also demonstrate the qualities of malleability (can be shaped by hammering) and ductility (can be drawn into wire).
