Covalent Compounds

Covalent Bonds Atoms of two nonmetals combined Held together by sharing electrons “co” means cooperate/share “valent” refers to the valence electrons Atoms bonded with covalent bonds are called molecules

Covalent molecules Atoms with covalent bonds share electrons to achieve an octet for each of them Some elements exist in nature as diatomic molecules = molecules that contain two like atoms * Note the names

Sharing Electrons Between Atoms of Different Elements The number of electrons that an atom shares and the number of covalent bonds it forms are usually equal to the number of electrons needed to acquire a noble gas arrangement

Exceptions Although the nonmetals typically form octets,… Some (P, S, Cl, Br, and I) can share more valence electrons and form stable valence shells of 10 or 12 electrons 1A 3A 4A 5A 6A 7A H 1 bond B 3 bonds C 4 bonds N O 2 bonds F Si P 3 (or 5) bonds S 2 (4 or 6) Cl, Br, I 1 (3 or 5) Bonds

Multiple Covalent Bonds In many covalent compounds, atoms may share 2 or 3 pairs of electrons to complete their octets Double bond  2 pairs of e- shared Triple bond  3 pairs of e- shared C, O, N, and S are most likely to form multiple bonds Atoms of hydrogen and the halogens do not form double or triple bonds

Naming Covalent Compounds 1st nonmetal uses its elemental name 2nd nonmetal uses its elemental name with the –ide ending Subscripts are expressed as prefixes placed in front of each name Prefixes for naming covalent numbers used in compounds 1 Mono 2 Di 3 Tri 4 Tetra 5 Penta 6 Hexa 7 Hepta 8 Octa 9 Nona 10 Deca

Ex) carbon + oxygen can form CO (carbon monoxide) or The names of covalent compounds need prefixes because several different compounds can be formed from the same two nonmetals Ex) carbon + oxygen can form CO (carbon monoxide) or CO2 (carbon dioxide) In the name of a covalent compound, the prefix mono is usually omitted on the 1st atoms name When the vowels o and o or a and o appear together, the first vowel is omitted

Practice naming covalent compounds Name each of the following covalent compounds: a) NCl3 b) N2O4 Nitrogen trichloride Dinitrogen tetroxide Write the formula of sulfur dichloride. SCl2

Naming and Writing Formulas Naming Binary Molecular Compounds The prefix tells how many atoms of each element are present in each molecule of the compound Carbon Monoxide vs. Carbon Dioxide Mono- indicates one oxygen Di- indicates two oxygens

Naming and Writing Formulas Guidelines for Naming Confirm the compound is a molecular compound (2 nonmetals) Omit mono- when the the formula contains only one of the first element in the name Add -ide to the second element in the formula Guidelines for Formula Writing 1) Use the prefixes in the name to tell you the subscripts in the formula

Naming and Writing Formulas Practice Write the name of these molecular compounds: NCl3 BCl3 NI3 SO3 N2H4 N2O3

Naming and Writing Formulas Practice Write the formulas for these binary molecular compounds: Phosphorus pentachloride Iodine heptafluoride Chlorine trifluoride Iodine dioxide Carbon tetrabromide Diphosphorus trioxide

Summary of naming rules Binary Compounds (may be ionic or covalent)  State the 1st element, followed by the 2nd element with an –ide ending If 1st element is  a metal = ionic compound nonmetal = covalent compound Ionic compounds  Is the 1st able to form more than one ion? … …if so, use Roman numerals to indicate charge Compounds with polyatomic ions use –ate or –ite endings (determined by # of oxygens) * Exception NH4+ written 1st Covalent compounds  Prefixes are needed to show # of atoms of each nonmetal in the formula

Organic Compounds