Chemical Bonding Part 1 Covalent Bonding Types of Chemical Bonds Covalent Bonds Single Polar Double NonPolar Triple Ionic Bonds Metallic Bonds Other Bonds InterMolecular orces first A PREVIEW & SUMMMARY of the 3 main types of bond: Ionic Bonds while keeping in mind: Atoms are unhappy if their outer energy level is not full!! Atoms only bond with other atoms in order to fill their outer energy level. An ionic bond is the attraction between an anion and a cation, which form after an electron is transferred from a metal to a nonmetal Covalent Bonds Metallic Bonding A covalent bond exists when two electrons are shared by nonmetallic atoms. Takes place in a SEA O MOBILE VALENCE ELECTRONS 1
Covalent Bonds: are formed when two atoms share a pair of electrons. always form between two nonmetal atoms. always form between atoms with similar electronegativity values. Time for an example: How many electrons does carbon need to be happy? 4 electrons! 6+ Time for an example: Vacancies 6+ Remember, H has 1 e (electron), and 1 p + (proton). 1+ Remember, H has 1 e (electron), and 1 p + (proton). Remember, H has 1 e (electron), and 1 p + (proton). Is H happy? Nope! 1+ How many vacancies does H have? 1!!! 1+ 2
OK, time for the big moment: Let s see how this looks If C has 4 vacancies, and H has 1, how many H can bond with C? 4!!! Hydrogen Let s see how this looks Now we need to add our other H s Hydrogen bonds with 4 hydrogens to form a methane molecule: Single, Double and Triple Bonds: a SINGLE covalent bond is formed by TWO electrons: Single, Double and Triple Bonds a DOUBLE covalent bond is formed by OUR electrons: 3
Single, Double and Triple Bonds a TRIPLE covalent bond is formed by SIX electrons: C C A water molecule contains two, single covalent bonds: Each bond consists of one pair of electrons being shared. Other Examples of Covalent Bonding: Diatomic Molecules Whenever an element bonds with itself, a diatomic molecule is created. Many important molecules are covalently bonded diatomic molecules, for example H 2, O 2, N 2, Cl 2 (atmospheric & other gases) Other Examples of Covalent Bonding: Diatomic Molecules Hydrogen(H 2 ) two electrons form a covalent bond two H atoms held together by a single covalent bond Other Examples of Covalent Bonding: Diatomic Molecules: Hydrogen(H 2 ) Oxygen(O 2 ) Covalent Bonding Double Bond 4
Covalent bonding Results from the sharing of a pair of valence electrons Between nonmetals only (and Hydrogen) Single, Double or Triple Bonds Unequal sharing is called a polar covalent bond (more on this later) Naming Covalent Compounds some stuff you already know: CO Monoxide CO 2 Dioxde SO 2 Sulfur Dioxide N 3 Nitrogen Trifluoride Prefixes used for covalent compounds: 1 Mono 2 Di 3Tri 4Tetra 5 Penta 6 Hexa 7 Hepta 8 Octa 9 Nona 10 Deca Rules for Naming Covalent Compounds 1. Name the first element (the least electronegative is first) (the furthest left on the periodic table.) 2. If there is more than one atom of that element, add a prefix. 3. Name the next element & add a prefix. (even if there is only one, add mono ) 4. Add the ide suffix. Examples: CCl 4 Tetrachloride P 2 O 5 Diphosphorous Pentoxide N 2 O 4 Dinitrogen Tetroxide LEWIS DOT STRUCTURES are sketches of molecules or atoms that show valence electrons as dots C Na P 4 S 10 Tetraphosphorous Decasulfide 4 valence e Sodium 1 valence e luorine 7 valence e 5
LEWIS DOT STRUCTURES are helpful to show how valence electrons are involved in bonding: Two atoms: One molecule: Single covalent bonds are drawn as single lines Remember: Single Covalent Bond = 2 electrons The Octet Rule Remember: Atoms only bond in order to fill their valence shell. In the case of Hydrogen, this means having 2 valence H : H electrons. (duet rule) : In the case of most other nonmetal elements this means getting 8 valence electrons (octet rule). Rules for Drawing Lewis Structures Use one pair of electrons to form a covalent bond between outside atoms and the central atom. 1. Calculate the total number of valence electrons for each atom, and add them up. Arrange the remaining electrons to complete the octets of the outside atoms. 2. If there are more than two atoms, start with central atom (usually the least electronegative but never hydrogen). If the central atom lacks an octet, then form double or triple bonds instead. Make sure all atoms have an octet, except Hydrogen, which always has 1 bond. Resonance structures Sometimes more than one correct Lewis structure can be drawn; especially if there are double and triple bonds. Example: In such a case we call the various structures resonance structures. 6