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Chemical Change

Chemical Change. 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,

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Chemical Change

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  1. 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, M4 Periodic Table: Chemical Change Slide 3 of 35

  3. Learning objectives • 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

  4. Learning objectives • Write word equations 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 • 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) M4 Periodic Table: Chemical Change Slide 5 of 35

  5. 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. • The most simple of these reactions is combination (or synthesis) reaction. • (When elements and/or compounds are just physical brought together, they form a mixture of course.) M4 Periodic Table: Chemical Change Slide 6 of 35

  6. Practice Question (7) • Balance the following formulas • BaCl • NH4O • NaS • AuAg • Iron III Oxide

  7. 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 M4 Periodic Table: Chemical Change Slide 8 of 35

  8. Combination Reaction • 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.

  9. 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 way 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 M4 Periodic Table: Chemical Change Slide 10 of 35

  10. Chemical Equation Sodium + oxygen  Sodium oxide • Everything to the left of the arrow is referred to as reactants and everything to the right product(s) • “” 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.”)

  11. Representing Reactions • Here are some more examples of word equations: • Hydrogen + oxygen  Water • Coal (carbon) + oxygen  Carbon dioxide • Zinc + Iodine  Zinc iodide • Aluminum + Iodine  Aluminum iodide • Aluminum + bromine  aluminum bromide M4 Periodic Table: Chemical Change Slide 12 of 35

  12. Representing Reactions • The other method of representing chemical reactions is to use the formula of the substances involved. • 2Na (s) + O2 (g)  2Na2O (s) • Is this balanced? • 2H2 (g) + O2 (g)  2H2O (l) • (Note hydrogen and oxygen and are diatomic elements)

  13. Representing Reactions • C (g) + O2(g) CO2 (g) • Zn (s) + 2I (s) ZnI2(s) • 2Al (s) + 6I (s) 2AlI3(s) • 2Al (s) + 6Br (l) 2AlBr3 (s) • The equations above are referred to as chemical (or symbolic) equations. M4 Periodic Table: Chemical Change Slide 14 of 35

  14. Representing Reactions • 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.

  15. State Symbols • 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. M4 Periodic Table: Chemical Change Slide 16 of 35

  16. 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. • 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. M4 Periodic Table: Chemical Change Slide 17 of 35

  17. 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. M4 Periodic Table: Chemical Change Slide 18 of 35

  18. + Combination Reaction • So a reaction between sodium and oxygen can be visualized as follows: • Na + O2 Na2O • What that means is that to form one unit of the compound sodium oxide, two sodium atoms are needed to combine with one atom of oxygen. • Each formula can be made to represent one fundamental particle. • Na represents 1 atoms of sodium, and O2 represents 1 moleculeof oxygen (which is 2 atoms). • Notice, as written, the equation shows the loss/destruction of one oxygen atom and creation of one sodium atom! M4 Periodic Table: Chemical Change Slide 19 of 35

  19. + Combination Reaction • Since oxygen atoms travel around in pairs (Diatomic), we must end up with two oxygen atoms in the number of units of the compound produced. • So, in the equation a molecule of oxygen is shown to produce two units of sodium oxide. Accounting for the number of oxygen atoms has meant the creation of sodium atoms. M4 Periodic Table: Chemical Change Slide 20 of 35

  20. + Combination Reaction: Balancing Equation • The creation of 3 sodium atoms, which we can balance by adding three more sodium atoms to the left. • Giving us the balanced equation: • 4Na + O2 2Na2O • A chemical equation must be balanced so as to not contradict the law of conservation of matter. M4 Periodic Table: Chemical Change Slide 21 of 35

  21. + Combination Reaction: Balancing Equation • A reaction between zinc and iodine can be visualized as follows: • Zn + I2 ZnI2 • Draw balanced diagrams to represent the following reaction: • Al + I2 AlI3 M4 Periodic Table: Chemical Change Slide 22 of 35

  22. Practice Question • Draw balanced diagrams to represent the following reaction: • Al + O2 Al2O3 M4 Periodic Table: Chemical Change Slide 23 of 35

  23. Combination Reaction: Metal + Nonmetal • In the lab you observed some dramatic combination reaction, one of which was that between zinc and iodine. • Zinc + Iodine  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  Aluminum iodide M4 Periodic Table: Chemical Change Slide 24 of 35

  24. 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  sodium oxide • Magnesium + oxygen  magnesium oxide • In other words, compounds of consisting of an element and oxygen are referred to as oxides. M4 Periodic Table: Chemical Change Slide 25 of 35

  25. Combination Reaction: Metal + Nonmetal • You also observed some reactions between other metals and non-metals: • zinc + sulfur  zinc sulfide • iron + sulfur  iron sulfide • In general then: • Metal + non-metal  metal and name of non-metal with –ide ending M4 Periodic Table: Chemical Change Slide 26 of 35

  26. 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. M4 Periodic Table: Chemical Change Slide 27 of 35

  27. Combination Reaction: Non-metal + non-metal • So what do you call a compound of hydrogen and oxygen combined together? • Hydrogen + oxygen  hydrogen oxide? • Not really, though that would make sense. • You all know it’s called water. M4 Periodic Table: Chemical Change Slide 28 of 35

  28. Combination Reaction • The names and the products of a reaction between two non-metals are not as easy to figure out and determine. • hydrogen (gas) + oxygen (gas)  water + • Other reactions were: • carbon + oxgyen  carbon dioxide + • This is the reaction that takes place when coal burns. M4 Periodic Table: Chemical Change Slide 29 of 35

  29. + + Combination Reaction • nitrogen + hydrogen  ammonia • Nitrogen + oxygen  nitrogen oxide • This reaction can take place in the engine of a car. • hydrogen + fluorine  hydrogen fluoride M4 Periodic Table: Chemical Change Slide 30 of 35

  30. Combination Reaction • hydrogen + chlorine  hydrogen chloride • hydrogen + bromine  hydrogen bromide • hydrogen + iodine  hydrogen iodide • sulfur + oxygen  sulfur dioxide • But notice that as long as the compound is made of two different elements, their names end in –ide. M4 Periodic Table: Chemical Change Slide 31 of 35

  31. Combination Reaction • 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.

  32. Practice Problem (33) • The next few slides show how compounds have different properties then the elements the are made of, they are examples, you do not need to learn them • Write the balanced chemical equation for each in one box on your assignment sheet

  33. Formation of Water •  Element: Oxygen, symbol: O; formula: O2 • Properties: • an odorless molecular gas at room temperature • transparent, clear, light passes through it • chemically reactive - very reactive when heated • 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 •  Compound: Water, H2O • Properties: • An odorlessliquid at room temperature • transparent, clear, light passes through it • not very chemically reactive, the compound is stable M4 Periodic Table: Chemical Change Slide 34 of 35

  34. 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 •  Element: Nitrogen, N; symbol: N, formula: N2 • Properties: • A odorless molecular gas at room temperature • transparent, clear, light passes through it • chemically reactive - very reactive when heated •  Compound: Ammonia, NH3 • Properties: • a characteristic pungent smelling gasat room temperature • transparent, clear, light passes through it • A relatively reactive compound M4 Periodic Table: Chemical Change Slide 35 of 35

  35. 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 •  Element: Oxygen, O;symbol: O; formula: O2 • Properties: • a gas at room temperature • transparent, clear, light passes through it • chemically reactive - very reactive when heated •  Compound: Carbon dioxide, CO2 • Properties: • a gas at room temperature • transparent, clear, light passes through it • not very chemically reactive, the compound is stable M4 Periodic Table: Chemical Change Slide 36 of 35

  36. Sulfur Dioxide • Element: Sulfur, symbol: S; formula: S. • Properties: • a solid at room temperature • yellow coloured • insoluble in water • chemically reactive when heated slightly •  Element: Oxygen, O; symbol: O; formula: O2 • Properties: • a gas at room temperature • transparent, clear, light passes through it • chemically reactive - very reactive when heated •  Compound: Sulfur dioxide, SO2 • Properties: • a gas at room temperature • transparent, clear, light passes through it • readily dissolves in water M4 Periodic Table: Chemical Change Slide 37 of 35

  37. Sodium oxide • Element: Sodium, symbol: Na; formula: Na. • Properties: • a solid at room temperature • silver coloured • very reactive (hence stored under oil) •  Element: Oxygen, O;symbol: O; formula: O2 • Properties: • a gas at room temperature • transparent, clear, light passes through it • chemically reactive - very reactive when heated •  Compound: Sodium oxide, Na2O • Properties: • a gray solid at room temperature • hygroscopic • readily dissolves in water M4 Periodic Table: Chemical Change Slide 38 of 35

  38. 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. M4 Periodic Table: Chemical Change Slide 39 of 35

  39. Signs of reaction • When you observed combination reactions, you would have noted the following signs of reaction • 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). M4 Periodic Table: Chemical Change Slide 40 of 35

  40. 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. M4 Periodic Table: Chemical Change Slide 41 of 35

  41. Na Sodium atom after losing 1 electron Sodium atom Na Mg Mg Metal atoms lose electrons • Metal atoms in general achieve noble gas structure by losing their valence electrons. Magnesium atom after losing 2 electrons Magnesium atom M4 Periodic Table: Chemical Change Slide 42 of 35

  42. F F Fluorine atom after gaining 1 electron Fluorine atom O O Oxygen atom after gaining 2 electrons Oxygen atom Nonmetal atoms either gains electrons • Non-metal atoms when reacting with metals achieve noble gas structure by gaining electrons. M4 Periodic Table: Chemical Change Slide 43 of 35

  43. …or share electrons • Non-metal atoms when reacting with other non-metal atoms, they achieve noble gas structure by sharing electrons between themselves. Cl H + H Cl Hydrogen & chlorine atoms sharing 2 electrons between them. Hydrogen atom Chlorine atom • We will have more to say about metals losing electrons, non-metals either gaining electrons or sharing electron when we look at other chemical reactions and bonding. M4 Periodic Table: Chemical Change Slide 44 of 35

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