Covalent Bonding Forming Molecular Bonds What is a

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 Non-polar Covalent e- are shared equally Polar Covalent e- shared unequally Ionic one atom takes efrom another Na e- Cl

Types of covalent bonds Single Covalent bonds- (also called sigma bonds) When a single pair of electrons is shared Ex: H H Group 7 A: will form single covalent bonds Group 6 A: will form two single covalent bonds Ex: H 2 O Group 5 A: will form three single covalent bonds Ex: NH 3 Ammonia Group 4 A: will form four single covalent bonds Ex: CH 4 methane

Types of covalent bonds continued… Multiple covalent bonds: Double or Triple bonds Double covalent bond- when two pairs of electrons are shared. Ex: O 2 (draw lewis structure) Triple covalent bond- formed when three pairs of electrons are shared between two atoms. Ex: N 2 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.

: Lewis dot structures : : : Rules for drawing dot structures: 1. Calculate the number of valence e- each atom contributes. Divide this number in half to get the number of pairs. ex: CBr 4 C=4 Br = 7 x 4 = 28 32 e 16 prs

: 3. Use pairs of e- (as single covalent bonds) to attach all the other atoms to the center atom. ex: CBr 4 : Br : C : : : Br 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.

Lewis dot structures continued… 2. Decide which element will be the center at usually the one that has fewer atoms or the lower electronegativity CH 4 SO 2 PCl 5

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

diatomic elements H 2 O 2 Br 2 F 2 I 2 N 2 Cl 2 Octet Rule: atoms share electrons in order to have 8 valence e- (2 for hydrogen)

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 first element 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’.

Naming Covalent Compounds Prefixes Subscript Prefix 1 Subscript Prefix mono- 6 hexa- 2 di- 7 hepta- 3 tri- 8 octa- 4 tetra- 9 nona- 10 deca- 5 penta- Note: When a prefix ending in ‘o’ or ‘a’ is added to ‘oxide’, the final vowel in the prefix is dropped.

1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca * Second element ends ‘ide’ * Drop –a & -o before ‘oxide’ Naming Binary Covalent Compounds: Examples N 2 S 4 dinitrogen tetrasulfide NI 3 nitrogen triiodide Xe. F 6 xenon hexafluoride CCl 4 carbon tetrachloride P 2 O 5 diphosphorus pentoxide SO 3 sulfur trioxide

Writing Chemical Formulas: A Review I. Ionic Compounds II. Covalent Compounds

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: Ø Binary compounds contain only two elements, both of which are nonmetals Ø When in covalent compounds Øatoms DO NOT have charges ØSubscripts are determined directly from the prefixes in the name.

1 Writing Formulas for Binary Covalent Compounds: Examples mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca * Second element ends in ‘ide * Drop –a & -o before ‘oxide’ nitrogen dioxide NO 2 diphosphorus pentoxide P 2 O 5 xenon tetrafluoride Xe. F 4 sulfur hexafluoride SF 6

Writing Formulas: Practice Analysis If “Yes” carbon tetrafluoride CF 4 prefixes covalent prefixes indicate subscripts sodium phosphate Na 3 PO 4 metal ionic balance charges 3 Na 1+ needed for 1 PO 43 - copper (I) sulfate Cu 2 SO 4 aluminum sulfide Al 2 S 3 dinitrogen pentoxide N 2 O 5 ammonium nitrate NH 4 NO 3 lead (IV) oxide Pb. O 2 iron (III) carbonate Fe 2(CO 3)3 metal present ionic balance charges 2 Cu 1+ needed for 1 SO 42* Are there prefixes present The compound is covalent: the prefixes give the subscripts. metal present ionic balance charges 2 Al 3+ needed for 3 S 2 - prefixes covalent prefixes indicate subscripts The compound is ionic: subscripts must be determined by balancing charges polyatomic ion present ionic balance charges 1 NH 41+ needed for 1 NO 31 - metal present ionic balance charges 1 Pb 4+ needed for 2 O 2 - metal present ionic balance charges 2 Fe 3+ needed for 3 CO 32 -