1. Chemistry FundamentalsPart 2:Basic Chemistry Concepts Chapter 8: Chemical Reactions and Physical Changes Essential Question: What are the basic chemistry concepts of food science? 1
2. Essential Information GPS: FS 3 – Students will discuss the basic chemistry concepts of food science. A. Describe the parts of an atom B. Describe solutions, heterogeneous mixtures, homogeneous mixtures and explain the similarities and differences C. Define and differentiate between chemical and physical changes in food D. Recognize chemical symbols, formulas, and equations for common elements found in food E. Compare and contrast elements and compounds and explain the difference between ionic and covalent bonds and compounds 2
3. Essential Information Key Questions: How do chemical reactions compare to physical changes? What are the parts of an atom? What is the mass of one mole of an element or compound? How are ionic and covalent bonds formed? What are the parts of a chemical equation? What are the differences between reversible and irreversible reactions and changes? 3
5. The Cycle of Change How do chemical reactions compare with physical changes? 5
6. Physical and Chemical Changes Chemical reaction – the change of substances into other substances Physical change – an alteration of a substance that does not change its chemical composition Chemical reactions produce one of the following three results: Elements join to form compounds Compounds break apart into elements Compounds form other compounds All chemical reactions involve the rearrangement of atoms 6
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8. What is the mass of a mole of an element or compound?7
9. Atoms: The Building Blocks of Matter Atoms – the smallest particle of an elements that retains its chemical properties Structure of Atoms: Made of even smaller parts called subatomic particles The three most important particles are: Protons – a particle that has a positive electrical charge; the number contained in an atom determines its identity; atomic number – the number of protons in an atom Neutrons – uncharged atomic particle; each atom can have different numbers of neutrons Protons and neutrons are located in the nucleus – dense core of an atom (plural = nuclei); protons give the nucleus a positive charge Electrons – negatively charged particle that moves around the nucleus; have almost no mass compared to protons and neutrons; determine whether a chemical reaction takes place 8
10. Atoms: The Building Blocks of Matter While atoms of one element are different from the atoms of any other, subatomic particles are not. A proton in carbon atom is identical to a proton in an oxygen atom. The same is true from electrons and neutrons. Energy Levels of Electrons: Opposite electrical charges attract Positively charged electrons in the nucleus hold the negatively charged electrons within the atomic structure. An atom stays neutral as long as it has an equal number of protons and electrons. 9
11. Atoms: The Building Blocks of Matter Energy Levels of Electrons: (cont.) Electrons move about the nucleus in regions of space called energy levels. The first energy level, which is closest to the nucleus, is lowest in energy. More energetic electrons occupy levels increasingly farther from the nucleus An electron in the third level has more energy than on in the second. This pattern continues through all of an atom’s energy levels Each energy level can hold only a certain number of electrons – 2 in the first, 18 in the third 10
12. Atoms: The Building Blocks of Matter Energy Levels of Electrons: (cont.) Most atoms are chemically stable, or unlikely to react with others, when they have 8 electrons in their outer most energy level. Hydrogen and Helium are exceptions – with just one energy level, their atoms achieve stability with only 2 electrons Atomic Mass Mass number – combining the total protons and neutrons in an atom’s nucleus Not every atom of the same element has the same mass number. Recall that while every atom of an element has the same number of protons, the number of neutrons may vary 11
13. Atoms: The Building Blocks of Matter Atomic Mass Mass numbers may also vary. Every atom of chlorine has 17 protons. If one chlorine atom has 18 neutrons, its mass number would be 35. A different chlorine atom with 16 neutrons would have a mass number of 33. Mass numbers are used to determine the atomic mass of an element. When the mass numbers of many chlorine elements were actually averaged, the number 35,453 resulted. This number forms the atomic mass of chlorine. Atomic mass – the average mass of a sample of atoms of that element found in nature Hydrogen, with the simplest atomic structure (one proton and no neutrons), has an atomic mass of 1.0. Carbon’s = 12.0 and Sulfur’s = 32.1 12
14. Atoms: The Building Blocks of Matter Atomic Mass Atomic mass and other facts about each element are found in a periodic table – a chart that arranges the elements by atomic number into rows and columns according to similarities in their properties. Elements with the same properties are placed in the same columns. The Mole Working with something as small as atoms and molecules requires a very large unit of measure – the mole Mole – the unit of measure used to count atoms or molecules; quantity equal to 6.02 x 1023 Written out – 602 followed by 21 zeros May be different in other properties – may have the same number; but may be vastly different in mass and volume 13
15. Atoms: The Building Blocks of Matter Moles and Mass When scientists work with a certain amount of an element or a compound, they often need to know its mass. They have a few rules to simplify this task: The mass of one mole of an element is called its molar mass and is equal to that element’s atomic mass in grams. To find the mass in grams of one mole of a compound, you must add the atomic masses of the elements in the compound. If a compound contains more than one mole of an element, then it must be multiplied by its subscript Determining molar mass is essential studying chemical reactions. Knowing the ratio of atoms and molecules in a reaction can help chemists determine the mass of elements and compounds needed to carry out that reaction. 14
17. How Compounds Form How are ionic and covalent bonds formed? What are the parts of a chemical equation? 16
18. How Compounds Form Compounds form when two or more elements join chemically. Their atoms give in to attractive forces strong enough to bind them. Chemical bonds – the forces that hold atoms together There are two types and each one produces a particular kind of compound. Ionic Bonding Covalent Bonding 17
19. How Compounds Form Ionic Bonding Atoms are most stable when their outer energy level contains eight electrons – without this number, it is likely to interact with another atom to satisfy this need. It may transfer the electrons in its outer level to another atom, or accept electrons from an atom With an equal number of protons and electrons, an atom is neutral. After electrons transfer, a donor atom has more positive protons in its nucleus than negative electrons and becomes positively charged The atom that accepts the extra electrons now has more negative electrons than positive protons and takes a negative charge Ions – charged particles 18
20. How Compounds Form Ionic Bonding With opposite electrical charges, these positive and negative ions are attracted and held together by an ionic bond – the bond formed by the transfer of electrons between atoms. Occurs only between atoms of different elements Atoms of metallic elements most easily achieve a stable energy level by losing electrons from their outer level. They tend to form positive ions Nonmetals generally achieve stability by gaining electrons Ionic compounds – compounds that result when metals and nonmetals bond ionically with each other; also called salts Ionic compounds properties are completely different from those of its parent elements Sodium chloride is a good example: Pure sodium is kept under oil to prevent it from reacting with oxygen and igniting. Chlorine is a poisonous gas best known for killing bacteria. The transfer of a single electron between the two, allows them to form a solid that is safe to eat. 19
21. Physical Changes What are the differences between reversible and irreversible reactions and changes? 20
