The Cautionary Tale of …  Would you be willing to sign a petition that demands either the strict control of, or a total ban on a substance that: 1.is a major component of acid rain 2.eventually dissolves nearly anything it comes into contact with 3.is lethal if accidentally inhaled 4.can cause severe burns in its gaseous state 5.has been found in tumors of terminal cancer patients

Why should we be cautious about what we hear/see?  Only give part of the picture  Not enough information  Source of info is unknown  Information is presented in a way that prevents other information from coming to light  Additional information/voices suppressed

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 1A3A4A5A6A7A H 1 bond B 3 bonds C 4 bonds N 3 bonds O 2 bonds F 1 bond Si 4 bonds P 3 (or 5) bonds S 2 (4 or 6) bonds 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   1 st nonmetal uses its elemental name   2 nd 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 1Mono 2Di 3Tri 4Tetra 5Penta 6Hexa 7Hepta 8Octa 9Nona 10Deca

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 CO 2 (carbon dioxide)   In the name of a covalent compound, the prefix mono is usually omitted on the 1 st 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) NCl 3 b) N 2 O 4 Nitrogen trichlorideDinitrogen tetroxide Write the formula of sulfur dichloride. SCl 2

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 1)Confirm the compound is a molecular compound (2 nonmetals) 2)Omit mono- when the the formula contains only one of the first element in the name 3)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: a)NCl 3 b)BCl 3 c)NI 3 d)SO 3 e)N 2 H 4 f)N 2 O 3

Naming and Writing Formulas Practice Write the formulas for these binary molecular compounds: a)Phosphorus pentachloride b)Iodine heptafluoride c)Chlorine trifluoride d)Iodine dioxide e)Carbon tetrabromide f)Diphosphorus trioxide

Summary of naming rules Binary Compounds (may be ionic or covalent)  State the 1 st element, followed by the 2 nd element with an –ide ending If 1 st element is    a metal = ionic compound   nonmetal = covalent compound Ionic compounds  Is the 1 st 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 NH 4 + written 1 st Covalent compounds  Prefixes are needed to show # of atoms of each nonmetal in the formula

Organic Compounds