1	M4 Periodic Table V: Chemical Change
2	Learning objectives Key Concepts: Combination, synthesis, decomposition, displacement, double displacement, precipitation, signs of reaction reaction, physical property, chemical property, element, compound, mixture, word equation, chemical equation, Word equation, chemical equation, reactant, product, Skills: Identify diagrammatic representation for element, compound and mixture Distinguish between element, compound and mixture Distinguish between physical change and chemical change Identify a chemical reaction
3	Learning objectives Write word for simple combination reactions between metals and non-metals given the names of the chemicals involved. Write chemical equations for simple combination reactions given the formula of the compounds (except those you are meant to memorize). Balance simple combination reactions given the formula of the chemicals involved using particle diagrams and the law of conservation of matter. Discuss signs of reaction (the four hints that indicate a chemical change)
4	Combination Reaction We will next start by considering a few variety of interactions between elements which produce compounds. Whenever elements and/or compounds interact, they are said to have undergone a chemical reaction. A chemical reaction produces a completely new substance or substances. (When elements and/or compounds are just physical brought together, they form a mixture of course.) The most simple of these reactions is combination (or synthesis) reaction. (There are about ten different types of chemical reactions all of which you will study about in MYP.)
5	Combination Reaction Combination reactions are ones where two different elements chemically combine to produce a single compound. Element A + Element B ® Compound containing A and B A metal can combine with a non-metal to form a compound Metal + Nonmetal ® Compound containing metal & nonmetal Two non-metals can combine to form a compound. Nonmetal A + Nonmetal B ® Compound containing nonmetal A & B Two metals cannot combine to form compounds however. (They do mix to give alloys, which is a mixture and not a compound.) The physical and chemical properties of the compound are usually different from those of the elements it is made from.
6	Chemical Equation You will study several different types of chemical reactions and learn to represent them using words or formula of the substances involved. The simplest is was of representing a reaction is using the names of the chemical involved (called word equation). A chemical equation is a chemical short-hand for a host of information For example, Sodium + oxygen ¾® Sodium oxide Everything to the left of the arrow is referred to as reactants and everything to the right product(s) “à” means produces or yields or gives or results in “+” on the left side means “reacts with” or “combines with” (If “+” appears on the right hand side it means “and.”)
7	Representing Reactions Here are some more examples of word equations: Hydrogen + oxygen ¾® Water Coal (carbon) + oxygen ¾® Carbon dioxide Zinc + Iodine ¾® Zinc iodide Aluminum + Iodine ¾® Aluminum iodide Aluminum + bromine ¾® aluminum bromide The other method of representing chemical reactions is to use the formula of the substances involved. 2Na _(g) + O_{2 (g)} à 2Na₂O _(s) 2H_{2 (g)} + O₂ _(g) à 2H₂O _(l)(Note hydrogen and oxygen and are diatomic elements)
8	Representing Reactions C _(g) + O₂ _(g) à CO₂_(g) Zn _(s) + I_{2 (s)} à ZnI₂ _(s) 2Al _(s) + 3I_{2 (s)} à 2AlI₃ _(s) 2Al _(s) + 3Br₂ _(l) à 2AlBr₃_(s) The equations above are referred to as chemical (or symbolic) equations. Notice a couple of things that’s different about a chemical equation compared to word equation: Chemical equation includes symbols in bracket next to the chemicals involved in the process Coefficients in front of the formula of the chemicals involved in the chemical process.
9	State Symbols AT THIS POINT, YOU DO NOT NEED TO BE ABLE TO REPRODUCE THE FORMULA OF COMPOUNDS! YOU WILL LEARN TO DO THAT LATER. The symbols in brackets are referred to as the (physical) state symbol. The state symbols indicate the physical state of the substances. s = Solid l = liquid g = gas aq = aqueous (dissolved in water, in other words in solution) You should by now know the physical states of most of the elements and be able to supply the state symbol for any element that appears in an equation.
10	State Symbols As far as compounds go all compounds of metals are solid. Compounds formed by the combination two non-metals however, can be solid, liquid or gas. However, most of those that you will have to work with and be able to recognize are gaseous. You will need to memorize them as you learn about their state. Water of course is liquid. But, carbon dioxide (CO₂) and carbon monoxide (CO), both oxides of carbons are gaseous. Both sulfur dioxide (SO₂) and sulfur trioxide (SO₃) are gaseous as well. Hydrogen sulfide (H₂S) is also gaseous. All halides of hydrogen (hydrogen chloride, HCl, hydrogen bromide, HBr, and hydrogen iodide, HI) are gaseous as well.
11	Coefficients Coefficients in front of the formula are required to conform to the law of conservation of matter. That is, since matter cannot be destroyed or created, atoms and molecules cannot be destroyed or created in a chemical process. The number of atoms at the end of a chemical process must be equal to the number of atoms in the beginning. For simple combination reaction, you can balance them by drawing (or imagining) particle diagrams.
12	Combination Reaction So a reaction between sodium and oxygen can be visualized as follows: Na + O₂ à Na₂O
13	Combination Reaction Since oxygen atoms travel around in pairs, we must end up with two oxygen atoms in the number of units of the compound produced.
14	Combination Reaction: Balancing Equation The creation of 3 sodium atoms, which we can balance by adding three more sodium atoms to the left.
15	Combination Reaction: Balancing Equation A reaction between zinc and iodine can be visualized as follows: Zn + I₂ à ZnI₂
16	Practice Question Draw balanced diagrams to represent the following reaction: Al + O₂ à Al₂O₃
17	Combination Reaction: Metal + Nonmetal In the lab you observed some dramatic combination reaction, one of which was that between zinc and iodine. Zinc + Iodine à Zinc iodide When a metal (such as zinc) and non-metal (such as iodine) combine to form a compound, the name of the compound is derived by writing the name of the metal first followed by the name of the non-metal whose last syllable is replaced by an –ide ending. Iodine therefore becomes iodide. Hence the name of a compound of zinc and iodine is zinc iodide. You also observed a reaction between aluminum and iodine. The word equation for that looks like this: Aluminum + Iodine à Aluminum iodide
18	Combination Reaction: Metal + Nonmetal So, names of all compounds formed by the combination of a metal and iodine have the format: name of metal followed by iodide. As a matter of fact, compounds containing iodine and a metal are referred to as iodides. That is, zinc iodide, aluminum iodide, sodium iodide, magnesium iodide are examples of iodides. You also observed some reactions between oxygen and other elements. Sodium + oxygen à sodium oxide Magnesium + oxygen à magnesium oxide In other words, compounds of consisting of an element and oxygen are referred to as oxides.
19	Combination Reaction: Metal + Nonmetal You also observed some reactions between other metals and non-metals: zinc + sulfur à zinc sulfide iron + sulfur à iron sulfide In general then: Metal + non-metal à metal and name of non-metal with –ide ending
20	Combination Reaction: Metal + Nonmetal Hydrogen becomes hydride. Nitrogen becomes nitride. Oxygen becomes oxide. Fluorine becomes fluoride. Phosphorus becomes phosphide. Sulfur becomes sulfide. Chlorine becomes chloride. Bromine becomes bromide.
21	Combination Reaction: Non-metal + non-metal So what do you call a compound of hydrogen and oxygen combined together? Hydrogen + oxygen à hydrogen oxide? Not really, though that would make sense. You all know it’s called water.
22	Combination Reaction The names and the products of a reaction between two non-metals are not as easy to figure out and determine.
23	Combination Reaction
24	Combination Reaction hydrogen + chlorine à hydrogen chloride hydrogen + bromine à hydrogen bromide hydrogen + iodine à hydrogen iodide sulfur + oxygen à sulfur dioxide But notice that as long as the compound is made of two different elements, their names end in –ide. A compound is different from a mixture in that the atoms in a compound are chemically bonded together, and that’s why the physical and chemical properties of the compound is markedly different from the elements from which it is made. In the next several slides we will look at properties of some elements and the compounds they form.
25	Formation of Water Element: Hydrogen, symbol: H, formula: H₂ Properties: an odorless molecular gas room temperature transparent, clear, light passes through it chemically reactive - very reactive when a small spark is provided
26	Formation of Ammonia Element: Hydrogen, H; symbol: H, formula: H₂ Properties: an odorless molecular gas room temperature transparent, clear, light passes through it chemically reactive - very reactive when a small spark is provided
27	Carbon dioxide Element: Carbon, symbol: C; formula: C. Properties: a solid (powder) at room temperature black coloured, absorbs all light, none passes through chemically reactive when heated slightly
28	Sulfur Dioxide Element: Sulfur, symbol: S; formula: S. Properties: a solid at room temperature yellow coloured insoluble in water chemically reactive when heated slightly
29	Sodium oxide Element: Sodium, symbol: Na; formula: Na. Properties: a solid at room temperature silver coloured very reactive (hence stored under oil)
30	Compound and mixture A mixture on the other hand retains the properties of the elements and/or compound it is made of. For example sea water is a mixture and it retains the saltiness of salt and fluidity of water. Vinegar is a mixture of acetic acid and water Air is a mixture of different gases (nitrogen, oxygen, argon and a few others). Alloys are mixtures of two or more metals. Steel is an alloy of iron, chromium and nickel; bronze: copper & tin etc.
31	Signs of reaction When you observed those dramatic demonstration and performed the other combination reactions, you would have noted the following signs of reaction and concluded that a chemical reaction (change) had taken place: change in color and/or production of a solid where there was no solid or a different colored solid from that already present in the mixture, and/or Bubbling or evolution of a gas that is colored or has an odor, and/or Change in energy--either production of energy in the form of sound energy (explosion) or generating heat energy (increasing temperature) or using up heat energy (decreasing temperature).
32	Why do elements react with one another? Elements react with each other because they are energetically unstable. Atoms of noble gases are energetically stable while the rest of the elements in the periodic table are not. Atoms of noble gases are energetically stable because their valence shells contain the maximum number of electrons that they can accommodate. So, atoms of other elements try to attain a similar electronic structure as those of noble gases and they do so by reacting with other elements. Atoms of other elements achieve the same electronic structure as a noble gas by either losing electrons, or gaining electrons or sharing electrons between themselves.
33	Metal atoms lose electrons Metal atoms in general achieve noble gas structure by losing their valence electrons.
34	Nonmetal atoms either gains electrons Non-metal atoms when reacting with metals achieve noble gas structure by gaining electrons.
35	…or share electrons Non-metal atoms when reacting with other non-metal atoms, they achieve noble gas structure by sharing electrons between themselves.