VIEWS: 0 PAGES: 4 POSTED ON: 7/27/2012
The "Street Chemist" Part-4 Families of Salt Compounds ROBERT BURKE Elements bond together ionically or covalently to form compounds. Compounds can be organized into families, which have similar characteristics and hazards. If you are familiar with the rules that place a compound into a particular family, you can encounter an unknown compound and know the hazards based upon family association. Metals and non- metals bond together ionically to form salts. Salts can be divided into six general salt families, each with their own characteristics and hazards. Salt families include the binary, binary oxide, peroxide, hydroxide, oxysalt, and cyanide salts. Generally all of the hazards associated with salt families are the result of a reaction of the salt and water. So the salt may not have significant hazards when dry, but may become very dangerous when in contact with water. Water reactions can cause the release of heat, corrosive liquid, poison liquid, or an oxidizer. When metals and non-metals bond ionically, the metal gives up its outer shell electrons to the non-metal. This leaves behind a stable outer shell in the metal, and the non-metal has a stable outer shell because of the electrons received from the metal. Formulas of ionically bonded salts have to be balanced. When a metal gives up an electron, there is now one less negatively charged electron in the atom then positive protons in the nucleus. Therefore, the metal has a positive charge in the compound. This is represented in the formula by a plus sign and a number above and to the right of the metal in the formula. When a non-metal receives an electron from the metal, there is now one more negative electron in the shells than positive protons in the nucleus. This results in the non-metal or non-metal radical having a negative charge. This is represented in the formula by a negative sign and a number above and to the right of the non-metal in the formula. Charges of atoms of elements are obtained from the Roman Numerals at the top of each column of the "Towers" portion of the periodic table. Each element in a column has the same charge. For example, family I the Alkali Metals each have one electron in their outer shell. Therefore, they have one electron to give up to the non-metal during bonding and have a +1 charge. Elements in family II are the Alkaline Earth Metals and each has two electrons in their outer shells to give up. This results in a +2 charge for those metal elements. Transitional elements have varying numbers of electrons in their outer shells and Ionic Bonding Graphic so the number at the top of the column of the transitional metals is of no help. A chart below shows possible numbers of electrons and their charges of some common transitional elements. Transitional Elements for Street Chemistry Element Possible Example Naming of Naming of Charges Compound New Old Copper +1 CuCl Copper I Cuprous +2 CuCl2 Copper II Cupric Iron +2 FeCl2 Iron II Ferrous +3 FeCl3 Iron III Ferric Mercury +1 HgCl Mercury I Mercurous +2 HgCl2 Mercury II Mercuric Tin +2 SnCl2 Tin II Stannous +4 SnCl4 Tin IV Stannic The naming of transitional metals also identifies the number of electrons in the outer shell of that metal element. For example, Copper can have 1 or 2 electrons in its outer shell. If there is one electron it is called Copper I, if there are two electrons, it is Copper II. An older naming system of transitional metals also exists (see chart above). This system uses an alternative name to indicate the different charges of some elements. For example, when a transitional element has two different potential charges, the lesser charge has an "ous" ending. The higher charge of the two has an "ic" ending. Using this system, copper I is referred to, as cuprous and copper II is cupric. Putting copper together with chlorine under the new and old naming system would yield copper I chloride or cuprous chloride. Copper II chloride would be cupric chloride under the old system. Radicals are one or more non-metal elements covalently bonded together and acting as a group. The elements as a group have an assigned charge to the group. This is represented in the formula by a negative sign and number above and to the right of the non-metal radical. In order to balance a salt compound, more than one atom of a given element may be required. This could result in different numerical values for the positive or negative numbers located above the compound formula. The actual numbers depend on how many atoms of the elements involved in the bonding were necessary to obtain the right number of electrons in the outer shells of the metal and non-metal in the compound. The reason for the bonding is to make sure each atom of each element has 2 or 8 electrons in the outer shell to satisfy the duet and octet rules of bonding. After the bonding is complete the positive and negative numbers at the top are removed if they are the same numerical value. For example, if there was a two above each compound symbol, they would cancel each other out and not be written. It is then just understood if there are no numbers there, then they were both the same. If the number above the element symbols in the compound is a one, it is understood and it is not written. If the numbers above the symbols in the compound are not the same, they are then "criss crossed" to balance the compound and placed at the lower right of the metal or non-metal symbol. Salt Families Binary Binary Peroxide Hydroxide Oxysalts Cyanide Oxide M+ M + Oxy M + NM M + (O2)-2 M + (OH)-1 M + CN-1 Oxygen Rad Not Oxy Ends in Ends in Ends in Ends in Ends in See Chart oxide Peroxide Hydroxide Cyanide "ide" WR= WR= CL, *Varies CL,RH, R WR=CL, RH Oxidizer Poison, CL RH O2 WR = Water Reactive CL = Corrosive Liquid RH = Release Heat RO = Release Oxygen *There is no specific hazard assigned to family, hazard must be researched in reference materials. Binary salts are made up of any metal and any non-metal with the exception of oxygen. Binary salts have a wide variety of hazards and are the exception to the family rule. Binary salts must be researched in reference sources to determine the exact hazard of the salt compound. Binary compounds are named by listing the metal first followed by the non- metal, which has been altered to end in "ide". For example, if the metal sodium were combined with chlorine the resulting compound would be called sodium chloride with a molecular formula of NaCl. It is the "ide" ending, which determines the binary salt family. If a compound has a metal in the formula and the non-metal ends in "ide" then it is a member of the binary salt family. Note that there are also non-salt compound names that end in "ide". The distinction is made by whether there is a metal or non-metal element in the compound. Calcium metal combined with the non-metal carbon would create the compound calcium carbide with a molecular formula of CaC2. You might notice that the balancing procedure for the salts does not fit for this compound. Just know that this compound has a peculiar bonding process and is the exception to the rule. (The formula listed for calcium carbide is correct.) Binary oxide salts are made up of any metal and the non-metal oxygen. Upon contact with water, binary oxides release heat (RH) and form a corrosive liquid (CL). They do not release oxygen because the oxygen present is tied up in the compound. Binary oxide salt compounds are named much the same as the binary salts. First you name the metal followed by the non-metal. In the case of the binary oxides, the only non-metal used is oxygen. So all binary oxides will end in "oxide". An example would be the metal potassium combined with oxygen produces the compound potassium oxide, K2O. Peroxide salts are made up of any metal and the peroxide radical. In the case of peroxide salts, two oxygen atoms bond together and act as one with a negative charge; O2 -2. Oxygen, you will remember, is one of the diatomic elements that cannot exist by themselves and many times will bond with each other to satisfy the octet rule of bonding. When a metal and non-metal O2 group bond together they form a peroxide salt compound. Peroxide salts in contact with water, release heat, form a corrosive liquid, and because there is excess oxygen, they release oxygen. This can be dangerous in a fire situation as oxygen can be released to accelerate the combustion process, making the fire more difficult to extinguish. Peroxide salts are named by placing the metal first and ending with the word "peroxide". For example, if the metal sodium were combined with the peroxide radical, the resulting compound would be sodium peroxide, Na2O2. Hydroxide salts are composed of any metal and the hydroxide radical. The hydroxide radical is made up of an oxygen and hydrogen covalently bonded together. This radical carries a negative one charge OH-1. When in contact with water, hydroxide salts release heat and produce a corrosive liquid. Hydroxide compounds are named with the metal first followed by the ending "hydroxide". Lithium metal combined with the hydroxide radical would produce the compound lithium hydroxide, LiOH. Oxysalts are made up of a metal and a non-metal covalently bonded oxy radical. Oxysalts are oxidizers. Oxysalts when in contact with water do not react violently, but rather dissolve in water. The danger occurs when these materials are dissolved in water and soak into a flammable material. Once the flammable material becomes dry, the oxysalt stays in the flammable material. If the material catches fire, the combustion is accelerated because of the oxysalt oxidizer in the material. Oxy radicals are shown on the chart below. Different radicals carry different charges ranging from -1, -2, and -3, and are listed on the chart by the charge they have. The radicals are named using the base state ending "ate". Therefore, FO3 is fluorate, ClO3 is chlorate, BrO3 is bromate, IO3 is iodate, NO3 is nitrate, MnO3 is manganate, CO3 is carbonate, SO4 is sulfate, and PO4 is phosphate. Oxy Radicals & Charges Oxysalts are named by the metal first and followed -1 -2 -3 by an ending found on the naming chart below. FO3 CO3 PO4 Names are based upon the number of oxygens in ClO3 SO4 the radical. For example, Magnesium metal BrO3 combined with the radical NO2 yields the compound IO3 magnesium nitrite. The ending is "ite" because there NO3 is one less oxygen than is found in the base state MnO3 NO3. If the radical used were NO, the compound would be named magnesium hyponitrite. The prefix "hypo" is added to the compound because the oxygen is two less than the base state of NO3. Naming Oxysalts The base state of an oxysalt is O3. Oxysalts that are at the base state end in +1 Oxygen_________Prefix "Per" _____ "ate" Ending Base _____________Ending "ate" "ate". For Example, Calcium metal -1 Oxygen_________ Ending "ite" combined with the oxy radical ClO3 would -2 Oxygen_________ Prefix "hypo"____ "ite" Ending be named calcium Chlorate, Ca(ClO3)2. Chlor indicates chlorine. In some cases a prefix is also added to the oxysalt name, again also based upon the numbers of oxygens in the radical. When an oxysalt radical has excess oxygen, usually O4, the prefix "per" is added to the non-metal radical and it ends in "ate". For example, if additional oxygen is added to the ClO3, it becomes ClO4, one above the base state. The prefix "per" is added and the ending remains "ate". The name of the compound would be Calcium Perchlorate, with a formula of Ca (ClO4) 2. Oxysalts also have to be balanced. Calcium has a charge of +2, while the oxy radical ClO4 has a charge of -1. Ca+2(ClO4)-1 These do not cancel out, so they have to be criss-crossed to balance the compound. Ca(ClO4)2 When the number of oxygens is less than the base state, the ending changes to "ite". For example, Calcium combined with the oxy radical ClO2 would be named Calcium Chlorite because of the one less oxygen compared to the base state. The formula would be Ca(ClO2)2. The charge of the oxy radical does not change even though the number of oxygen has changed. If the number of oxygens is two below the base state, a prefix "Hypo" is added to the name. Calcium metal and CLO (remember anytime there is just one of anything, the one is understood and not represented in the formula) combine to form Calcium Hypochlorite with a formula of Ca(ClO)2. Once again, the charge does not change. The naming rules hold true no mater what the metal is, which is attached to an oxy radical. Cyanide salts are made up of a metal and the cyanide radical, CN-1. The name of the compound starts with the metal and ends with the word "cyanide". Cyanides are deadly poisonous salts and dissolve in water to form a hydrogen cyanide solution. Cyanides are found as solids and liquids. When liquids are heated they can product a toxic gas. Potassium metal combined with the cyanide radical would be called potassium cyanide with a formula of KCN. Since both potassium and cyanide charges are 1, they cancel out and there are no subscripts in the formula.
Pages to are hidden for
"The 'Street Chemist' Part-4"Please download to view full document