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Covalent Bonding

Covalent Bonding. Forming Molecular Bonds. What is a covalent bond?. The chemical bond that results from the sharing of electrons Non-metals combine to acquire a full valence shell of 8 valence electrons Example:. 7 valence e -. 8 valence e -. Degree of sharing. e - are shared equally.

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Covalent Bonding

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  1. Covalent Bonding Forming Molecular Bonds

  2. What is a covalent bond? The chemical bond that results from the sharing of electrons Non-metals combine to acquire a full valence shell of 8 valence electrons Example: 7 valence e- 8 valence e-

  3. Degree of sharing e- are shared equally e- shared unequally one atom takes e- from another Na Cl e-

  4. Types of covalent bonds Single Covalent bonds- (also called sigma bonds) When a single pair of electrons is shared Ex: H H Group 7A: will form single covalent bonds Group 6A: will form two single covalent bonds Ex: H2O Group 5A: will form three single covalent bonds Ex: NH3- Ammonia Group 4A: will form four single covalent bonds Ex: CH4- methane

  5. Types of covalent bonds continued… Multiple covalent bonds: Double or Triple bonds Double covalent bond- when two pairs of electrons are shared. Ex: O2 (draw lewis structure) Triple covalent bond- formed when three pairs of electrons are shared between two atoms. Ex: N2 shares three pairs of electrons. Pi bonds π- multiple bond consists of one sigma and one pi bond. triple bond- one sigma and two pi bonds. The shorter the bond the stronger the bond. Triple bonds are shorter.

  6. : : : : : Lewisdotstructures : Rules for drawing dot structures: • Calculate the number of valence e- each atom • contributes. Divide this number in half to get • the number of pairs. 32 e- ex: CBr4 C = 4 16 prs Br = 7 x 4 = 28

  7. 3. Use pairs of e- (as single covalent bonds) to attach all the other atoms to the center atom. : ex: CBr4 : Br : : : Br : C Br : : : Br : : : 4. Put lone pairs of e- on the outside atoms until each atom has 8 electrons (4 pairs) or 1 pair on hydrogen. 5. Put any leftover pairs on the center atom so that it also has 4 prs around it.

  8. Lewis dot structures continued… 2. Decide which element will be the center at usually the one that has fewer atoms or the lower electronegativity CH4 SO2 PCl5

  9. Lewis dot structures continued… CH4 What is the central atom? C • How many valence electrons does it have? • 4 • How many hydrogens are there? • 4 • How many valence electrons do each have? • 1 H H H Now, join the electrons with a bond H How many sigma bonds are there? 4

  10. diatomic elements H2 O2 Br2 F2 I2 N2 Cl2 OctetRule: atoms share electrons in order to have 8 valence e- (2 for hydrogen)

  11. Naming Covalent Compounds Covalent compounds are named by adding prefixes to the element names. ‘Covalent’ means both elements are nonmetals. A prefix is added to the name of the firstelement in the formula ONLY if more than one atom of it is present. A prefix is ALWAYS added to the name of the second element in the formula The second element will use the form of its name ending in ‘ide’.

  12. Naming Covalent Compounds Prefixes Note: When a prefix ending in ‘o’ or ‘a’ is added to ‘oxide’, the final vowel in the prefix is dropped.

  13. Naming Binary Covalent Compounds:Examples dinitrogen tetrasulfide N2S4 NI3 nitrogen triiodide XeF6 xenon hexafluoride CCl4 carbon tetrachloride P2O5 diphosphorus pentoxide SO3 sulfur trioxide

  14. Writing Chemical Formulas: A Review I. Ionic Compounds II.CovalentCompounds

  15. Writing Formulas for Covalent Compounds The names of covalent compounds contain prefixes that indicate the number of atoms of each element present. • First element: • if there is only one atom of that element in the formula (its subscript will be 1) and there should NOT be a prefix • Second element: • will ALWAYS have a prefix • will ALWAYS end in -ide • Remember: • Binary compounds contain only two elements, both of which are nonmetals • When in covalent compounds • atoms DO NOT have charges • Subscripts are determined directly from the prefixes in the name.

  16. Writing Formulas for Binary Covalent Compounds:Examples nitrogen dioxide NO2 diphosphorus pentoxide P2O5 xenon tetrafluoride XeF4 sulfur hexafluoride SF6

  17. Writing Formulas: Practice carbon tetrafluoride CF4 prefixes  covalent  prefixes indicate subscripts Na3PO4 sodium phosphate metal  ionic  balance charges  3 Na1+ needed for 1 PO43- copper (I) sulfate Cu2SO4 metal present  ionic  balance charges 2 Cu1+ needed for 1 SO42- aluminum sulfide Al2S3 metal present  ionic  balance charges 2 Al3+ needed for 3 S2- dinitrogen pentoxide N2O5 prefixes  covalent  prefixes indicate subscripts ammonium nitrate NH4NO3 polyatomic ion present  ionic  balance charges  1 NH41+ needed for 1 NO31- lead (IV) oxide PbO2 metal present  ionic  balance charges 1 Pb4+ needed for 2 O2- iron (III) carbonate Fe2(CO3)3 metal present  ionic  balance charges 2 Fe3+ needed for 3 CO32-

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