BONDING

  • ·         molecules are the smallest units of a substance that still possess the fundamental chemical and physical properties of the substance
  • ·         molecules can be chemically broken down into simpler constituents called atoms
  • ·         atoms have much different properties when they’re isolated than when they’re components of a molecule
  • ·         elements are substances that consist of atoms of only one kind
  • ·         living matter tends to have common elements in it – C, H, O, N, P, and S
  • ·         it was once thought that atoms could not be broken down into smaller components, hence the name “atom” meaning “indivisible”
  • ·         however, today it is known that atoms can be broken down into their sub-atomic constituents:  electrons, protons, and neutrons
  • ·         electrons are negative in charge and possess negligible mass
  • ·         protons are positive in charge and possess approximately the same mass as neutrons, which have no charge
  • ·         protons and neutrons combine to form the nucleus – which is 99.9% of the mass of the atom, but occupies less than 1% of its volume
  • ·         using statistics, scientists can determine the most probable location of electrons in regions of space called orbitals
  • ·         they are able to determine regions of space where they are most likely to exist
  • ·         these fixed, 3-dimensional, regions of space around the nucleus are called orbitals 
  • ·         orbitals can only accommodate 2 electrons
  • ·         each energy level that surrounds a nucleus of an atom possesses subshells that contain these orbitals
  • ·         for example, energy level one possesses one subshell, (the s subshell), which in turn, is the first orbital, energy level two possesses two subshells, (the s and the p subshell), therefore 4 orbitals, the s, and the three p orbitals, energy level three possesses three subshells, (the s, the p, and the d subshell), therefore nine orbitals, the one s, the three ps, and the five ds, etc.
  • ·         the 1st orbital of every energy level has the same shape, the 2nd orbital has another distinct shape
  • ·         the maximum number of electrons that each energy level can hold can be calculated using 2n2, where n is the energy level
  • ·         for example, energy level 3, alone, can hold a maximum of 2(3)2 = 18 electrons
  • ·         an atom that has three energy levels can hold a maximum of 2(1)2 + 2(2)2 + 2(3)2 = 28 electrons
  • ·         the arrangement of electrons in the orbitals is called an atom’s electron configuration 
  • ·         the outermost orbitals contain the electrons furthest away from the nucleus of an atom     
  • ·         the orbitals that exist on the outer-most level contain the electrons that are responsible for the interaction of atoms to form molecules
  • ·         electrons found in these outer-most orbitals are called valence electrons
  • ·         these electrons are called valence electrons
  • ·         they are the ones involved in the chemical reactions of that atom
  • ·         the chemical stability of an atom is determined by the arrangement of an atom’s valence electrons
  • ·         atoms that have completely filled orbitals are more stable, and less reactive than atoms with half-filled, or incomplete orbitals
  • ·         all the elements in group 18 of the periodic table have a full set of electrons in their valence shell, therefore they are chemically stable
  • ·         all other elements in the universe have incomplete outer orbitals, therefore are reactive
  • ·         the most reactive elements are those that have one or two more than the full amount, or one or two less than the full amount
  • ·         these are found in the first and second column (group), and the sixteenth and seventeenth column (group)
  • ·         notice that the elements in each column possess the same number of valence electrons
  • ·         elements can become chemically stable by either taking, losing, or sharing valence electrons
  • ·         the elements on the left of the periodic table will lose the appropriate number of electrons to elements of the right side of the periodic table (excluding the last column of course) so that they will possess the full set number
  • ·         for example, if a sodium atom was in contact with a chlorine atom, the sodium would lose one electron to the chlorine, resulting in a stable number of 10 electrons (just like neon)
  • ·         consequently, the chlorine will pick up one electron and have a stable number of 28 electrons (just like argon)
  • ·         as a result, sodium becomes a cation with a positive one in charge, and chlorine becomes an anion with a negative one charge
  • ·         positive sodium is attracted to negative chloride, resulting in a force of attraction that keeps them together called an ionic bond
  • ·         the compound that results is sodium chloride – an ionic compound where each atom is chemically stable
  • ·         the force that keeps oppositely charged ions together is called an electrostatic force of attraction - it is not a true molecular bond
  • ·         molecular forces of attraction are forces that result from the overlapping of valence orbitals (sharing of electrons) between two atoms
  • ·         for example, if a carbon atom were in contact with two oxygen atoms, neither would lose or gain electrons
  • ·         instead, the carbon would share two electrons with one oxygen, and two with the other
  • ·         the region of space where the sharing of electrons takes place is called an intramolecular bond, also known as a covalent bond
  • ·         groups of atoms held together by covalent bonds are called true molecules -- 
  • ·         the forces that hold atoms together in a compound are called intramolecular forces of attraction