Covalent Bonding

What is Covalent Bonding? Covalent Bonding occurs when two atoms share valence electrons, forming an electrically-neutral compound Covalent bonding is different than ionic bonding because: 1) neutrally-charged atoms share, not electrically- charged ions 2) the valence electrons are actually shared, they are not transferred from a cation to an anion, like in ionic bonding 3) Covalent bonding occurs in bonds formed between nonmetals -- ionic bonds are always metal/nonmetal or involve polyatomic ions

Why Do Atoms Covalently Bond? Covalent bonding occurs for two reasons: 1) Covalent bonds involve nonmetals bonding to nonmetals, both of which have nearly-full valence energy levels -- neither atom is capable of giving up electrons to form a cation -- there are also no valence electrons available to form anions 2) Covalent bonds form from atoms with high electron affinity -- the pull of the nucleus keeps the electrons in the atom

Examples of Covalent Bonds We can draw covalent bonds using our Lewis Structures For example, let’s draw the covalent bond in water, H2O H + H + O H O H Each hydrogen has 1 valence electron and the oxygen has 6 valence electrons If each hydrogen shares its electron with oxygen, then oxygen has 8 electrons and is happy In return, oxygen shares 2 of its electrons (one to each hydrogen), giving hydrogen a full valence shell of 2 electrons, making hydrogen happy

Image of Covalent Bonding in Water

What About More Difficult Molecules? What about a compound like C2H6, how would we show that? We can use curved arrows to show the movement of electrons into a “shared” position -- it also helps to use different colors to represent different atoms H H H C C H Notice how I circle the electrons around each atom to make sure that all have a full valence shell

Number of Bonds Notice in both our water molecule and our molecule of ethane (C2H6), each atom shared only two electrons with each other individual atom -- this “pair” of shared electrons is a covalent bond Sometimes, however, in order to satisfy the octet rule and have a full valence shell, atoms need to share more than one pair of electrons -- if atoms in a compound share one pair of electrons, it is called a single bond -- if atoms in a compound share two pairs of electrons, it is called a double bond (4 electrons shared) -- if atoms in a compound share three pairs of electrons, it is called a triple bond (6 electrons shared)

What you MUST draw to get credit! Step 1 Step 2 Cl Cl Cl Cl *use two different colors or symbols for the electrons Step 3 Step 4 Cl2 Cl – Cl

Practice Drawing Covalent Bonds Use Lewis Structures to draw the covalent bonds in the following molecules: Oxygen gas (O2) 2) Nitrogen Gas (N2) 3) Carbon Dioxide (CO2)

Naming Covalent Compounds Simple binary (two different element) covalent compounds are really easy to name 1) The first word is the same as the name of the first element in the compound -- because it’s not metal-nonmetal, whichever element is further left on the table goes first -- oxygen IS (almost) NEVER the first word 2) The second word is the name of the second element in the compound, with the ending changed to –ide 3) Finally, both words in the compound get a prefix based on how many atoms of each there are in the compound -- if there is only 1 atom of the first element, it DOES NOT receive a prefix of mono-

Prefixes in Chemical Names mono 1 di 2 tri 3 tetra 4 penta 5 hexa 6 hepta 7 octa 8 nona 9 deca 10

Practice Writing the Names of Covalent Compounds -- H2O -- CCl4 -- NH3 -- P5O2 -- C3H8 Dihydrogen Monoxide Carbon Tetrachloride Nitrogen Trihydride Pentaphosphorus Dioxide Tricarbon Octahydride

Practice Writing the Formula From the Compound Name It’s also really easy to go the other direction given the name: For example: -- Disulfur pentoxide -- Carbon trifluoride S2O5 CF3