LecturePLUS Timberlake Covalent Bonding LecturePLUS Timberlake

LecturePLUS Timberlake I CAN write a formula for and name a covalent (molecular) compound. LecturePLUS Timberlake

LecturePLUS Timberlake Covalent Bonds Recently we worked with IONIC COMPOUNDS which form when positive CATIONS combine with negative ANIONS. Not ALL compounds involve ions. In COVALENT BONDING, valence electrons are shared between two atoms. Electrons are NOT transferred from one atom to another, so they do not develop “+” or “-” charges as do ions. Generally form between TWO NONMETAL ELEMENTS from GROUPS 14, 15, 16, and 17 but can involve elements FROM OTHER GROUPS. Covalent compounds are also called MOLECULAR COMPOUNDS. LecturePLUS Timberlake

LecturePLUS Timberlake EXAMPLE Two Hydrogen atoms move close together to SHARE valence electrons. H + H H H LecturePLUS Timberlake

LecturePLUS Timberlake The SAME TWO ATOMS can share DIFFERENT NUMBERS of electrons. There is more than one possible formula combination for the same group of atoms. For example, NITROGEN and OXYGEN can form several different compounds: NO NO2 NO3 N2O N2O2 N2O3 N2O4 N2O5 If we named this NITROGEN OXIDE, which one would we be talking about? LecturePLUS Timberlake

Naming Covalent (Molecular) Compounds In order to name a COVALENT compound, we follow the same basic rules as for BINARY IONIC compounds….with one added step. Since the same group of atoms can bond in different proportions, we must indicate HOW MANY OF EACH ATOM there is in the compound. LecturePLUS Timberlake

Naming Covalent Compound 1. Name the first element by its name, adding a NUMBER PREFIX ONLY IF THERE IS MORE THAN ONE ATOM. 2. Name the second element by its name, but: A. Change the ending to IDE. B. Add a NUMBER PREFIX to tell how many, even if there is only one! LecturePLUS Timberlake

Number Prefixes for Covalent Compounds 1 – Mono 2 – Di 3 – Tri 4 – Tetra 5 – Penta 6 – Hexa 7 – Hepta 8 – Octa 9 – Nona 10 –Deca LecturePLUS Timberlake

LecturePLUS Timberlake When adding prefixes, the “A” or “O” of the prefix may need to be DROPPED if the element starts with a VOWEL, such as: Hexa added to OXIDE becomes: Hexoxide NOT Hexaoxide LecturePLUS Timberlake

LecturePLUS Timberlake Practice Problems Example Write the formula for: Trinitrogen Pentachloride Tri = 3 Penta = 5 nitrogen chloride = chlorine So this compound needs 3 NITROGEN and 5 CHLORINE The 3 and 5 are the SUBSCRIPTS in the formula. N3Cl5 LecturePLUS Timberlake

LecturePLUS Timberlake WRITE the formula for these Covalent Compounds: (To make it easier, prefixes are colored in these practice problems) Click HERE for a PERIODIC TABLE. 1. carbon monoxide 2. carbon dioxide 3. phosphorus trichloride 4. carbon tetrachloride 5. dinitrogen monoxide LecturePLUS Timberlake

LecturePLUS Timberlake 1. CO carbon monoxide 2. CO2 carbon dioxide 3. PCl3 phosphorus trichloride 4. CCl4 carbon tetrachloride 5. N2O dinitrogen monoxide LecturePLUS Timberlake

LecturePLUS Timberlake MORE PRACTICE PROBLEMS Write the correct formula for the following Covalent compounds. 1. triphosphorus monoxide 2. phosphorus pentoxide 3. diphosphorus pentoxide 4. dichlorine heptoxide 5. dichlorine tribromide 6. silicon tetroxide 7. carbon tribromide 8. antimony disulfide LecturePLUS Timberlake

Diatomic Elements Some elements, when not bonded to other elements, bond to another atom of their own kind. These are known as DIATOMIC ELEMENTS. There are 8 naturally existing diatomic elements: ALL of family 17 (Halogen Family). Oxygen, Nitrogen and Hydrogen These elements should be written as: F2, Cl2, Br2, I2, At2, O2, H2, N2 when they are NOT part of a compound.

LecturePLUS Timberlake Pure vs Polar Covalent When two atoms share an electron, the ELECTRONEGATIVITY value of each atom determines how closely the electron is pulled toward one atom or the other. Recall Electronegativity [Eneg] is the measure of the attraction one atom has for another’s valence electrons. SEE CHART NEXT SLIDE FOR Eneg Values. LecturePLUS Timberlake

Electronegativity Values LecturePLUS Timberlake

LecturePLUS Timberlake Determining Bond Type To determine the type bond between any two atoms, find the difference between their Eneg values: 0 to 0.5 - PURE Covalent – the e- is shared at an equal distance between both atoms. 0.51 to 1.99 – POLAR Covalent – the e- is shared closer to one atom than the other…this gives the atom the e- is closest to a slightly NEGATIVE charge [delta -] and the one the e- is father away from a slightly POSITIVE charge [delta +]. 2.0 or greater – the e- is completely transferred from one atom to the other and forms an IONIC BOND. LecturePLUS Timberlake

LecturePLUS Timberlake Practice Problems Use Eneg values to predict the type of bond that would form between each pair of atoms: 1. Ca and Br ____________ 2. H and O ______________ 3. Pb and S ______________ 4. Au and S_______________ 5. Sn and I ______________ 6. C and H _______________ 7. B and H _______________ 8. Fr and F _______________ 9. N and Al _______________ LecturePLUS Timberlake