Covalent Compounds
These types of compounds are formed by chemical bonding of non-metal atoms to other non-metal atoms. As a result, a covalent bond is formed by the sharing of electron pairs (usually one e- from each element). The 2 non-metals are the same type, so they’re buddies… and buddies share!!
Covalent Bonds…why share? To obey the“Octet Rule” which states: atoms tend to gain, lose, or share e- to acquire a full set of valence e- (in most cases, 8 e-). They become isoelectronic (their configuration looks like) to an inert gas.
Covalent Bonds…how to show sharing? This sharing can be shown using “Lewis dot diagrams” which show just the valence electrons as dots around the symbol of the element. Each symbol only has 4 available spots around it, and each spot can hold a max of 2 e- Remember the bus-seats!!
Covalent Bonds…how to show sharing? Recall: Each symbol only has 4 available spots around it, and each spot can hold a max of 2 e-. Remember the bus-seats!! (Nobody pairs up till all seat at least have 1 e-) Eg.
How do you quickly draw a Lewis Dot structure??? This works for all elements in row 1,2, and 13-18. The last digit of the row number is the number of valence electrons the atom has. Eg. Oxygen is in row 16, so it has 6 valence e- (6 dots in lewis structure) Eg. Magnesium is in row 2, so it has 2 valence e- (2 dots in lewis structure) O Mg
Try some … Remember, up to 4 e-, you put separately on each side of the symbol, once you get to 5, you have to start pairing up. 1) Magnesium 2) Nitrogen 3) Flourine 4) Argon Single e- = Bonding pair N Double e- = Lone pair Mg F 8 e- = Stable Octet!! Ar
H Try Some!! F F F A Flourine atom A Calcium atom A Flourine ion Draw the Lewis structures for: A Flourine atom A Calcium atom A Flourine ion A Calcium Ion Hydrogen Flouride F Ca 1- F 2+ Ca H F
Each shared pair of electrons form a single covalent bond (line). Most covalent compounds’ formulas are difficult to predict without the names, but Lewis dot diagrams can be helpful when making predictions: E.g. Predict the compound H2O… Each shared pair of electrons form a single covalent bond (line).
Try the Lewis structure for CCl4… Bonding pair – 2 electrons paired where each is from a different element – they have bonded Lone pair – 2 electrons paired where both belong to the same atom!
How would you draw… NH3 H N H H CHOH H C O Hint : Make it symmetrical!! Hint : Carbon is always the backbone (central part of a Lewis structure if it is present!)
4. Naming covalent compounds involves a few simple rules: The more “metallic” of the non-metal elements is named first, that is, the element that loses e- more easily (less electronegative) Electronegativity is the ability to take e- from another atom. So…if you have high electronegativity – you are a real taker (very non-metal/negative atom!) e- High Electronegativity N M
Electronegativity
4. Naming covalent compounds: The element furthest to the left in a row is more metallic, also the element furthest down in a group/family. Eg. N is further left than O So… N is more metallic(less Electronegative) and goes 1st… N2O3 S is further down than O So… S is more metallic(less Electronegative) and goes 1st… SO
4. Naming covalent compounds: To tell the number of atoms of each element present in the covalent compound prefixes are used (see p. 246) MEMORIZE THESE PREFIXES!!! 1 2 3 4 5 6 7 8 9 10 Mono Di Tri Tetra Penta Hexa Hepta Octa Nona Deca
4. Naming covalent compounds: Change the ending of the second element in the compound to “-ide” e.g. oxygen oxide nitrogen nitride sulfur sulfide chlorine chloride *If the first element has only 1 atom, don’t put the prefix mono in front of it! Otherwise, put prefixes in front of everything else!
Examples: SO2 Sulphur Dioxide C2H4 Dicarbon Tetrahydride SF5 Sulfur PentaFluoride Dinitrogen Trioxide N2O3
5. Notice that prefixes must be used when naming covalent compounds as the elements charges cannot always be used to predict the chemical formula.
Now you try!! Hebden Pg 75 # 35,41,44,48,52,66,74,80,84,86 104,112,118,126,134,138. Final Review!! Do Pg 76 odds!!