Chemical Nomenclature

Transcription

1 Chemical Nomenclature Learn names you will Review: Valence electrons (the outer most electrons) are responsible for the interaction between atoms when forming chemical compounds. Another way to say that is that valence electrons are the electrons that participate in chemical bonding. The Octet Rule explains that every atom seeks a full valence shell. It is the attaining or loss of valence electrons that will satisfy the octet rule. The question now becomes: How do atoms gain a noble gas electron arrangement, or an octet? Answer: Through Chemical Bonding! A chemical bond is a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds them together. Ultimately resulting in a noble gas electron arrangement for all atoms involved. Matter Exists as Atoms, Metals, Ions, or Molecules Nobel gases actually exist as individual atoms. Remember, it is the interactions between the valence electrons of different elements to gain an octet that determine how the element will react with other elements. Nobel gases have an octet, therefore, they do not need to interact with other atoms to be energetically favorable. Matter Exists as Atoms, Metals, Ions, or Molecules We commonly work with pure metals. How is it then that only noble gases exist as atoms when pure metals are very common? Do they not exist simply as atoms? Unfortunately, no; they must shift their electrons around endlessly to gain a pseudooctet called Metallic Bonding. Matter Exists as Atoms, Metals, Ions, or Molecules While metal atoms can achieve a pseudooctet with delocalized valence electrons, allowing for a stable elemental form, metals rarely exist as pure substances. Rather, they exist as ions by completely giving away their valence electrons to nonmetal atoms. The transfer of electrons results in the formation of Ions; cations (+) and anions (). The resulting electrical attraction that then pulls cations and anions together is called ionic bonding forming ionic compounds. 1

2 Matter Exists as Atoms, Metals, Ions, or Molecules Ionic Bonds While nonmetal atoms prefer to take electrons from metal atoms forming ions, this is not always an option. Given that all nonmetal atoms seek to gain electrons in order to gain an octet, when nonmetal atoms are forced to interact with only other nonmetal atoms, they are forced to share electrons between them forming a covalent bond resulting in the formation of molecules. Here we see the formation of sodium chloride from sodium and chlorine. The ionic compound is formed as the electronegative chlorine atom takes an electron from the sodium atom. Metals vs. Nonmetals The simplest wholenumber ration of ions in a compound is called a formula unit. Since the sodium is +1 and the chlorine is 1, the ratio of cations to anions in sodium chloride is 1:1. Therefore, the formula unit for sodium chloride is NaCl; or, one sodium per one chloride ion. When atoms lose or gain electrons, they become ions. Cations are positive and are formed by elements on the left side of the periodic chart (metals). Anions are negative and are formed by elements on the right side of the periodic chart (nonmetals). But, not all ionic compounds are formed between ions of equal but opposite charge. Observe magnesium in group 2. The octet rule states that all atoms seek the electron configuration of the nearest noble gas, which is neon for magnesium. 12 Mg 2 p y To obtain an octet, magnesium gives up its two valence electrons to be like neon which has an octet in the next lowest energy level. 12 Mg 2 Mg Mg e 2 py The result is a cation with a 2 + charge. 3s 3s 9 9 F Fluorine also wants to be like neon; however, fluorine is electronegative must gain an electron to be like neon forming a 1 anion to obtain its octet. F + 1e F F 2 py 2 py So, given magnesium forms a 2+ ion and fluorine forms a 1 ion what would be the formula unit for a compound created between magnesium and fluorine? 2

3 Writing Formulas Because compounds are electrically neutral, one can generally determine the formula of a compound this way: The charge on the cation becomes the subscript on the anion. The charge on the anion becomes the subscript on the cation. If these subscripts are not in the lowest wholenumber ratio, divide them by the greatest common factor. Knowing the charges on ions Charges for representative elements can be determined from their group number. Charges on transition metals must be learned. Names, formulas and charges on polyatomic ions must be learned Charges on Representative Atoms Using a new reference periodic table, identify the charges for all representative metals and nonmetals using their group numbers. Transition metals can sometimes have more than one charge. This is due to the movement of electrons from lower energy levels to higher energy levels, ultimately changing the number of valence electrons for the atom. You will have to memorize the common charges on the transition metals. 3

4 Not all ions are monatomic. Sometimes a group of atoms that are bonded together can gain or loose electrons collectively. The result is a group of bonded atoms with a charge, known as a polyatomic ion. There are 11 polyatomic ions for which you will need to be able to identify the chemical formula, charge and name. Look at your Common Ion Reference and identify the eleven ions you are responsible for We will eventually learn where polyatomic ions come from, but for now, all you need to do is be able to recognize them. Naming Polyatomic Ions The names of polyatomic ions must be memorized. However, a trend does exist. Notice, when there are more than one polyatomic ions that differ only in the number of oxygens, the ion with the fewer oxygens has an ite suffix and the ion with the greater number of oxygens has an ate suffix. For Example: Nitrate vs. Nitrite What about ionic compounds formed from polyatomic ions? We treat the polyatomic ions as whole units by placing parenthesis around them and balancing them as they were individual atoms For Example: Magnesium and Phosphite could combine to form magnesium phosphite. Charges are: Mg 2+ and (PO 3 ) 3 Therefore, the chemical formula should be Mg 3 (PO 3 ) 2 Write the correct formula unit for all possible ionic compounds formed by the combination of the following: 1.Aluminum and hydroxide 2.Phosphide and strontium 3.Acetate and cobalt 4.Iron and sulfite Careful, remember that cations are always listed first. Naming Monatomic Ions Monatomic ions are single atoms that have gained or lost electrons. Monatomic cations, formed from metal atoms are named using the atomic name For example: Na Na + and are both called Sodium Monatomic transition metal cations are named the same way however, since transition metals may have more than one charge, the charge on the metal must be included in parenthesis using roman numerals following the name. For example: Fe 2+ Fe 3+ and are named Iron (II) and Iron (III) 4

5 Monatomic anions formed from nonmetals are named using the root of the atomic name with an ide suffix For example: S 2 N 3 Cl Are Sulfide, Nitride, and Chloride. Name the following ions: Mg 2+ CO 2 3 Cu + K + Br OH O 2 NO 2 Sn 4+ Mn 3+ Hg 2+ I P 3 NH + 4 Zn 2+ Nomenclature of Ionic Compounds 1. Write the name of the cation. 2. If the cation can have more than one possible charge, write the charge as a Roman numeral in parentheses. 3. If the anion is an element, change its ending to ide; if the anion is a polyatomic ion, simply write the name of the polyatomic ion. lets put it all together Write all possible ionic compounds that could be formed by the following pairs and name them correctly: 1.Cyanide and potassium 2.Ammonium and fluorine 3.Calcium and sulfur 4.Phosphate and cobalt 5.Hydrogen phosphate and gold Nomenclature of Molecules Because molecules do not contain ions, there are no charges to determine the formulas for the compounds. Learn more names you will No Ions! Therefore, in order to name molecules we must use prefixes to denote the number of atoms in a molecular compound. 5

6 Naming Molecular Compounds List atoms in order of increasing electronegativity Use prefixes to denote the number of atoms in the molecule. (mono, di, etc ) The last atom is given an ide suffix Drop o or a from prefix for atoms beginning with a vowel Omit the prefix mono when there is only one of the first (least electronegative) atom Molecular Prefixes: 1 mono 6 hexa 2 di 7 hepta 3 tri 8 octa 4 tetra 9 nona 5 penta 10 deca Lets try naming the following molecules: 1.CCl 4 2.P 4 S 8 3.SF 6 4.SiO 3 5.Molecule made from 1 sulfur and 2 chlorine atoms 6.H 3 N Nomenclature of Acids Learn even more names you will Acids An acid is defined as any molecule that can produce Hydrogen ions in solution. NonOxyanionic acids = do not contain oxygen in the resulting anions formed by the ionization of the molecule Oxyanionic acids = contain oxygen in the resulting anions formed by the ionization of the molecule. It is the interaction of these special molecules with water that make them acids. For Example: HNO 3 H + (aq) + NO 3 (aq) When hydrogen nitrate (HNO 3 ) is placed in water, H + and NO 3 are formed. Notice when hydrogen nitrate is placed in water, it is called nitric acid since it produces H + and NO 3, a polyatomic ion called Nitrate. You have already started to learn the names of some common acids Nonoxyanionic (Binary) Acids Oxyanionic Acids HF Hydrofluoric Acid HNO 3 Nitric Acid HCl Hydrochloric Acid HNO 2 Nitrous Acid HBr Hydrobromic Acid H 2 SO 4 Sulfuric Acid HI Hydroiodoic Acid H 2 SO 3 Sulfurous Acid H 2 S Hydrosufuric Acid H 3 PO 4 Phosphoric Acid H 3 N Hydronitric Acid H 3 PO 3 Phosphourous Acid H 3 P Hydrophosphoric Acid H 2 CO 3 Carbonic Acid HCN Hydrocyanic Acid HC 2 H 3 O 2 HCH 3 CO 2 Acetic acid What polyatomic ion is formed when each acid above looses hydrogen? 6

7 Nonoxyanionic (binary) acids are hydrogenated nonmetals with the exception of a few, such as cyanide. They are named with the hydro prefix followed by the anion name replacing the ide suffix with ic acid Oxyanionic acids contain oxygen and usually have multiple combinations of oxygen with the central atom. Oxyanionic acids are named by replacing the ate suffix with ic acid or the ite suffix with ous. Example: Notice: no hydro prefix Nitrate Nitric Acid Nitrite Nitrous Acid 7