* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Scientific Principles: Chemical Properties
Resonance (chemistry) wikipedia , lookup
Gas chromatography–mass spectrometry wikipedia , lookup
Rutherford backscattering spectrometry wikipedia , lookup
Electronegativity wikipedia , lookup
Isotopic labeling wikipedia , lookup
Metallic bonding wikipedia , lookup
Chemical potential wikipedia , lookup
Hydrogen-bond catalysis wikipedia , lookup
Process chemistry wikipedia , lookup
Organic chemistry wikipedia , lookup
Drug discovery wikipedia , lookup
Water pollution wikipedia , lookup
Rate equation wikipedia , lookup
Lewis acid catalysis wikipedia , lookup
Artificial photosynthesis wikipedia , lookup
Freshwater environmental quality parameters wikipedia , lookup
Abundance of the chemical elements wikipedia , lookup
Inorganic chemistry wikipedia , lookup
Electron configuration wikipedia , lookup
Chemical element wikipedia , lookup
Water splitting wikipedia , lookup
Periodic table wikipedia , lookup
Biochemistry wikipedia , lookup
Molecular dynamics wikipedia , lookup
Electrochemistry wikipedia , lookup
Click chemistry wikipedia , lookup
Extended periodic table wikipedia , lookup
Electrolysis of water wikipedia , lookup
Bioorthogonal chemistry wikipedia , lookup
Chemical reaction wikipedia , lookup
Photosynthetic reaction centre wikipedia , lookup
Chemical bond wikipedia , lookup
Hypervalent molecule wikipedia , lookup
Physical organic chemistry wikipedia , lookup
IUPAC nomenclature of inorganic chemistry 2005 wikipedia , lookup
Transition state theory wikipedia , lookup
History of chemistry wikipedia , lookup
Stoichiometry wikipedia , lookup
Chemistry: A Volatile History wikipedia , lookup
History of molecular theory wikipedia , lookup
1 Goals & Objectives • To explain the Periodic Table of the Elements • To identify and explain how chemical symbols, formulas and equations are used in food science • To discuss elements, compounds, mixtures and formulas • To compare elements and compounds • To analyze chemical and physical changes in food • To examine the occurrence of specific chemical reactions 2 Main Menu 3 Basic Chemistry Principles 4 Atoms • Are the basic unit of matter • Consist of a dense, central nucleus composed of protons and neutrons • Are surrounded by a cloud of electrons 5 Components of Atoms • Include: – neutrons- large particles with no net charge located in the nucleus – protons- large, positively charged particles located in the nucleus – electrons- small, negatively charged particles located in atomic orbitals 6 Elements • Are pure substances consisting of one type of atom • Cannot be broken down or changed into another substance • Combine with other elements to form compounds 7 Compounds • Are substances composed of two or more elements in specific ratios and bonded together through chemical forces – Example: Carbon dioxide is always composed of one carbon atom and two oxygen atoms • Are classified as either covalent or ionic in foods 8 Covalent Compounds • Are also known as molecular compounds • Occur between the non-metal elements • Share the electrons from each atom • Are molecules 9 Ionic Compounds • Occur between metals and nonmetals • Are held together by ionic bonds – electrons are donated from one atom to another giving one atom an overall negative charge and the other atom an overall positive charge • Contain atoms in which the total number of electrons is not equal to the number of protons • Can consist of one element or multiple elements such as NaCl 10 Ions • Are either positively or negatively charged • Can be a single atom (monatomic ion)or multiple atoms (polyatomic ion) – ions of many elements and compounds exist such as hydrogen, sodium, ammonium and sulfate 11 Pure Substances • Can be formed from elements or compounds • Consist of only one component with definite physical and chemical properties • Have the same composition throughout – E x a m p l e : O2 o r p u r e w a t e r 12 Mixtures • Are substances held together by physical forces – this means individual molecules are near each other without altering their chemical structure • Can be homogeneous or heterogeneous Homogeneous: mixtures which are the same throughout, with identical properties throughout the mixture Heterogeneous: mixtures which have different properties when sampled from different areas 13 Mixtures & Pure Substances Example • Tap water contains molecules which are not water molecules, making it a mixture • Distilled water contains only water molecules making it a pure substance 14 Bonds • Between atoms influence the molecule’s properties • Are classified as: – hydrogen – covalent – ionic – polar 15 Bonds • Example of this difference are hydrogen and covalent bonds – In a covalent bond, each atom equally shares the combined electrons; this type of bond is harder to break than a hydrogen bond. – Hydrogen bonds are commonly found between water molecules and proteins. The bond is the main reason for the properties of water and instrumental in the ‘unzipping’ of DNA. This bond is only about five to ten percent of the strength of a covalent bond. 16 Periodic Table 17 Periodic Table • Was created by Russian Chemist Dmitri Mendeleev in 1869 • Displays all of the known elements • Arranges all of the elements based on certain properties • Provides a framework to classify, organize and compare chemical behavior • Can be used in all fields of science 18 Periodic Table • Uses a unique chemical symbol to identify each element • Arranges elements from left to right and top to bottom in order of increasing atomic number – the order generally coincides with increasing atomic mass • Has rows called periods and columns called groups 19 Chemical Symbol • Is a shortened version of the name of an element • Represents an element in chemical formulas • Uses only one or two letters to represent an elements – for example, Hydrogen, Nitrogen and Oxygen are represented by H, N and O – if two elements have the same first letter, two letters comprise the symbol • for example, Calcium and Chlorine both start with a “c” but are represented by Ca and Cl 20 Atomic Number • Is the number of protons in an atom • Defines the element – for example: • all carbon atoms have six protons so its atomic number is six • all oxygen atoms have eight protons so its atomic number is eight 21 Atomic Mass • Is the average mass of an the protons and neutrons present in an element • Is measured in atomic mass units (amu) – Atomic mass units measure the approximate mass of one proton or neutron 22 Periods • Are the rows of the Periodic Table • Contain elements which have the same number of atomic orbitals for its electrons • Are given a period number – there are seven periods in the Periodic Table Atomic orbitals: shell which holds electrons Period number: the highest unexcited energy level for an electron in the element 23 Groups • Are the columns of the Periodic Table and are also known as families • Contain elements which share common properties • Are elements which have the same number of electrons in their outer orbital – the outer electrons are called valence electrons • Have Roman numerals listed above each group in the Periodic Table to indicate how many valence electrons are present • for example, group VA will have five valence electrons 24 Valence Electrons • Are the electrons located in the outermost occupied shell in an atom • Participate in chemical bonding • Determine the properties and chemical reactivity of the element • Aid in dividing the elements into representative elements and nonrepresentative elements 25 Major Families of Elements • Alkali Metals – are located in Group One – are very reactive – include the following elements: • • • • • • Lithium (Li) Sodium (Na) Potassium (K) Rubidium (Rb) Cesium (Cs) Francium (Fr) 26 Major Families of Elements • Alkaline Earth Metals – are located in Group Two – are the second most reactive group of elements – include the following elements: • • • • • • Beryllium (Be) Magnesium (Mg) Calcium (Ca) Strontium (Sr) Barium (Ba) Radium (Ra) 27 Major Families of Elements • Transition Metals – are located in the middle portion of the periodic table – are very hard – have high melting and boiling points 28 Major Families of Elements • Halogens – are very reactive – can be found in Group 17 – include the following elements: • • • • • Fluorine (F) Chlorine (Cl) Bromine (Br) Iodine (I) Astatine (At) 29 Major Families of Elements • Noble Gases – can also be called inert gases – are located in Group 18 which is also called Group Zero – are not reactive – include the following elements: • • • • • • Helium (He) Neon (Ne) Argon (Ar) Krypton (Kr) Xenon (Xe) Radon (Rn) 30 Major Families of Elements • Lanthanide Series – consist of 15 elements – can be found naturally occurring on Earth – has one radioactive element 31 Major Families of Elements • Actinide Series – consist of 15 elements – are all radioactive compounds – include some elements which are not found in nature 32 Chemical Formulas & Reactions 33 Chemical Formulas • Are a combination of elemental symbols and subscript numbers that are used to show the composition of a compound • Represent compounds – for example, the chemical formula f o r a l u m i n u m o x i d e i s Al2O3 • this means there are two aluminum atoms and three oxygen atoms 34 Ionic Compounds • Are composed of cations and anions • Are held together by the strong attraction of the positive and negative charges of the ions • Are neutral compounds • Are formed between metals and nonmetals – for example: sodium chloride or table salt (NaCl) Cation: ion with a positive charge Anion: ion with a negative charge 35 Chemical Formulas • Have a charge sum of zero – the positive and negative charges cancel each other out • for example: if a bond was formed between Mg+2 and Cl– to equal out the charges it would take 2 Cl- and 1 Mg+2 – so the chemical formula would be MgCl2 Hint: Always use the charges when writing a chemical formula. 36 Chemical Formulas • Polyatomic ion example – a bond is made between lithium Li+1 and sulfate S O 4 - 2 • to equal out the charges it would take two L i + 1 and 1 S O 4 - 2 • so the chemical formula would be L i 2S O 4 Hint: When working with polyatomic ions, DO NOT break it up or change the numbers in the ion. 37 Chemical Formulas • Covalent or molecular compound example – prefixes give the number of each element present in a molecule • carbon dioxide = C O 2 • dinitrogen monoxide = N 2 O • dichloride heptoxide = C l 2 O 7 38 Prefix Help Chart 39 Chemical Reactions • Occur when a chemical change occurs • Begin with one compound and turn it into another • Can include ions, molecules or pure atoms 40 Chemical Reaction Rate • Is the speed at which the reaction occurs – a lower reaction rate means the molecules combine at a lower speed than a reaction with a higher rate • Can be influenced by the collision theory – states that the more collisions in a system, the more likely combinations of molecules will happen • the higher the number of collisions, the faster the reaction will occur 41 Factors Affecting Reaction Rate • Include the following: – concentration – temperature – pressure 42 Concentration • Increases the rate of reaction if there is more of a substance in a system – there is a greater chance for the molecules to collide • Decreases the rate of reaction if there is less of a substance in a system – there is a decreased chance for the molecules to collide 43 Temperature • Increases the rate of reaction if the temperature is increased – the atoms or molecules will move more and are more likely to collide • Decreases the rate of reaction if the temperature is decreased – the atoms or molecules move slower and collide less 44 Pressure • Increases the rate of reaction when pressure is increased – increases the number of collisions between the atoms or molecules • Decreases the rate of reaction when the pressure is decreased – the atoms or molecules will not hit each other as often 45 Reaction Rate • Can be any of the following: – forward rate • the rate of the forward reaction when reactants become products – reverse rate • the rate of the reverse reaction when products become reactants 46 Reaction Rates • Net rate – the forward rate minus the reverse rate • Average rate – the speed of the entire reaction from start to finish • Instantaneous rate – the speed of the reaction at one moment in time 47 Chemical Reactions • Happen in several steps – the rate for each step should be measured • the rate-limiting step is the slowest step in the reaction and can determine the overall rate of reaction 48 Stoichiometry • Is the study of the amounts of substances involved in reactions • Helps you to figure out how much of a compound you need or how much you started out with 49 Stoichiometry Example • To make sodium chloride (NaCl), you start out with two ions Na+ and Cl- and end up with the ionic compound NaCl • When you look at the chemical formula, you see that it takes one atom of sodium to combine with one item of chlorine • Stoichiometry aids us in determining the amounts of substances needed to fulfill the requirements of the reaction • Stoichiometry tells us that if you have 100 atoms of sodium and only one atom of chlorine you can only make one molecule of sodium chloride. 100 Na + + 1 Cl NaCl + 99 Na + 50 Stoichiometry Example • Let’s say you are mixing two hydrogen gas molecules ( H 2 ) and one oxygen gas molecule ( O 2 ) and add a spark to it. • You would have this equation: 2H2 + O2 • In order to make water you need two hydrogen atoms for each oxygen to get the H2O chemical formula • Therefore the chemical reaction will yield two H 2 O 2H2 + O2 2 H 2O 51 Equilibrium • Occurs when two reactants combine to make a product and the products then break apart and turn back into the reactants – the reactants combining is a forward reaction and the products breaking apart is a reverse reaction • Exists when the forward reactions equal the rate of the reverse reaction 52 Catalysts • Increase reaction rate • Lower the amount of energy needed for a reaction to occur • Aid a reaction in reaching its activation energy Activation Energy: the energy required to make a reaction happen 53 Inhibitors • Decrease rate of reaction • Have the ability to stop a reaction from occurring • Help to control the rate of reactions 54 Food Chemistry 55 Food Chemistry • Is a systematic evaluation and understanding of water, carbohydrates, lipids, proteins, minerals and vitamins as they undergo chemical interactions during harvest, processing, storage and distribution • Is the study of chemical processes and interactions of all biological and nonbiological components of food • Encompasses the chemical makeup of food 56 Food Chemistry • Is based upon the following components of food: – water – carbohydrates – lipids – proteins – enzymes – vitamins 57 Water • Is a major component of food • Is an excellent location for bacterial growth and food spoilage to occur • Can be measured by obtaining the water activity of a food • Must be controlled in foods to aid in food preservation • Is controlled in foods by dehydration, freezing and refrigeration 58 Water • Is important in cooking and food preparation • Uses include: – removing debris and the washing of foods – a substance in which to cook food – a solvent to disperse and dissolve flavor additions – adding moisture to foods 59 Water • Can be either hard or soft – hard water • any water containing an appreciable quantity of dissolved minerals – soft water • any water in which the only positively charged ion is sodium Fun Fact: Rain water is considered “soft” until it reaches the ground where it picks up minerals 60 Hard Water • Commonly has high levels of calcium and magnesium • Can cause build up on fixtures such as faucets and shower heads • Decreases the effectiveness of soaps and laundry detergents 61 Hard Water • Found in almost 85 percent of American communities • Can be corrected by adding a water softener – Sodium or potassium ions are bonded to resin beads. Hard water runs over the beads and the minerals in the water cling to the beads, releasing the sodium and potassium ions into the water 62 Soft Water • Does not contain any dissolved minerals • Increases the life expectancy of plumbing systems and appliances which use water • Decreases: – soapy residue on clothes – mineral deposits on bathroom and kitchen fixtures – amount of soap and detergents used 63 Water • Is found in three states: – liquid – gas – solid • Can be transformed from a solid by the heat of fusion and from a liquid to a gas by the heat of vaporization 64 Heat of Fusion • Is the amount of energy required to transform a substance from a solid to a liquid • Is measured in Joules or calories • For water is 334 Joules per gram or 79.7 calories per gram 65 Heat of Vaporization • Is the amount of energy required to transform a substance from a liquid to a gas at the boiling point of the substance • Is measured in Joules or calories • For water is 2260 Joules per gram or 539 calories per gram 66 Heat of Vaporization • For water, is greater than the heat of fusion – Water has many unique chemical properties. For more information see: The United States Geological Survey Water Science for Schools 67 Carbohydrates • Are organic compounds which consist of carbon, hydrogen and oxygen • Are classified as monosaccharides, disaccharides, oligosaccharides and polysaccharides • Complete numerous functions such as providing energy 68 Carbohydrates • Can be used as thickening agents, sweeteners and for texture in foods • Form pastes when a mixture of ground starch and water is heated – Heat is necessary for paste formation 69 Paste Formation • Begins when the starch granule swells with the intake of water • Proceeds when the granule absorbs the maximum amount of water and releases amylose • Completes when the starch granule implodes • Increases the viscosity of a mixture 70 Paste Formation • Necessary for the creation of such foods as: – breakfast cereals – pastas – sauces 71 Lipids • Are a group of naturally occurring molecules such as: – fats and oils – waxes – sterols – monoglycerides – diglycerides – phospholipids • Are naturally hydrophobic 72 Lipids • Are commonly referred to as fats • Come from both animal and plant sources • Provide tastes and textures to foods • Have a wide range of cooking temperatures • Can be used as a cooking medium when melted at high temperatures 73 Lipids • Are important in food preparation • Provide a pleasant mouth feel and flavor to foods • Provide the highest amount of useable calories per gram Fun Fact: Mouth feel is the sum of a food’s physical and chemical reactions in the mouth. Texture is the actual physical feeling of a food in the mouth. 74 Lipids • Can: – prevent foods from sticking to cookware – create fluffy and moist or flaky baked goods – transfer heat to food – thicken or emulsify sauces 75 Lipids • Are available for cooking in liquid and solid forms • Must be observed closely while using as temperature can have a negative effect • Have different smoke points • Possess properties which can be altered by light, temperature and usage Smoke Point: temperature at which cooking fats and oils begin to smoke, emit odors and chemical structures break down 76 Temperature • Melts solid fat when increased • Inconsistences over time can cause chemical changes in the fat resulting in smell, taste and texture changes • At high degrees, degrades cooking fats over time 77 Temperature • Can cause the fat in food products to separate from the food – example: cheddar cheese cooked for a long period of time at a high temperature will release fat, become tough and rubbery, then crumble • Ranges for each cooking fat is different, so make sure you keep this in mind when choosing a cooking fat 78 Proteins • Are organic compounds made of amino acids arranged in a linear chain and folded into a globular form • Are essential for growth and survival • Can be found in legumes, meat, poultry and seafood 79 Proteins • Are used in cooking for texture, taste, appearance and nutritional content • In food preparation can be used: – as a base for a food product – as binding agent – to alter the texture of a food product 80 Proteins • Are denatured in the cooking process • Can be used as emulsifiers – egg yolks are used to bind oil and water in mayonnaise • Found in wheat are responsible for the texture of baked goods and pastas 81 Proteins • Must be present for the Maillard reaction to take place • Can be isolated from legumes, such as soybeans, and added to other protein sources, such as chicken, to change the texture and nutritional content of the final product Maillard Reaction: the coagulation of denatured proteins with sugars resulting in a distinct flavor and browned color; seen in caramelized onions and dairy based caramels 82 Enzymes • Are proteins which serve as catalysts used in converting processes from one substance to another • Reduce the time and energy required to complete a chemical process • Are used in baking, brewing, dairy production and fruit juices 83 Vitamins • Are nutrients required in small amounts for essential metabolic reactions in the body • Are either water or fat soluble • Can prevent disease 84 Physical Changes • Are any changes not involving a change in a substance’s chemical identity • Occur when objects undergo a change which does not change their chemical nature • Involves a change in physical properties – physical properties include the following: • • • • • • • texture shape size color volume mass weight 85 Common Physical Changes in Food • Include the following: – cutting – mashing – boiling – melting – freezing 86 Freezing • Involves storing a food below the freezing point of water – safest temperature of freezer storage is below 0°F • Results in water transforming from a liquid state to a solid state • Can have adverse effects on food quality – texture change, especially if food is not frozen quickly – altered color – freezer burn if exposed to air – increased food preparation time to account for defrosting time 87 Chemical Changes • Occur when bonds are broken and new bonds are formed between different atoms • Take place in everyday food production • Include the following common food reactions: – Nonenzymatic browning – leavening – fermentation 88 Nonenzymatic Browning • Is browning caused by heat degradation of sugars or by the reaction between reducing sugars and a free amino group • Is commonly found in foods • Increases when there is a rise in temperature and an increase in pH above 6.8 89 Leavening • Gives breads, cakes, muffins, pancakes and other foods the ability to rise and increase in volume • Occurs mainly during cooking • Involves a water or gas expanding for rising to occur 90 Leavening • Agents include: – baking powder – baking soda – baker’s ammonia – potassium bicarbonate – yeast – sourdough starter 91 Baking Powder • A combination of baking soda, cream of tartar and cornstarch • Comes in several types – single action- chemical reaction occurs when the powder comes in contact with moisture – double action- chemical reaction occurs in two stages: • first when the powder is moistened • second proceeds when heated – phosphate- reacts when the powder encounters moisture 92 Baking Powder • Ingredients all play a different role – cream of tartar is the acid salt in the baking powder and reacts with the baking soda in the presence of moisture – cream of tartar/baking soda reaction produces carbon dioxide – cornstarch absorbs any excess moisture which may enter the reaction 93 Baking Powder • Can drastically affect the taste of a baked good – makes food bitter and coarse textured if over used • Is best used in foods which are not overly acidic • Will lose effectiveness with age due to moisture interaction 94 Fermentation • Is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts or bacteria under anaerobic conditions • Implies the action of microorganisms is desirable • Is used in preservation techniques to create lactic acid in sour foods or for use in pickling foods 95 Resources “Chemical Properties”.Elmhurst College. Virtual Chembook.” (2003). Retrieved from: http://www.elmhurst.edu/~chm/vchembook.html “Physical and Chemical Properties”. Class notes. Indiana University Northwest. (2010). Retrieved from: http://www.iun.edu/~cpanhd/C101webnotes/matter-andenergy/properties.html “What is Food Chemistry?”. (2010). Deb Dommel. Retrieved from: http://www.math.unl.edu/~jump/Center1/Labs/WhatisFoodChemist ry.pdf “Food Chemistry: Principles and Applications”. (2000). Genevieve Christen & J. Scott Smith. 96 Acknowledgements Production Coordinator: Production Manager: Megan Mitchell Maggie Bigham Project Coordinator: Maggie Bigham Graphic Designer: Executive Producers: Gordon Davis, Ph.D., Jeff Lansdell Megan Mitchell © MMXI CEV Multimedia, Ltd. 97