Unit 2 – Chemistry and You

1. Unit 2 – Chemistry and You

2. A. Nature of Science "is the search for the truth“ Chemistry is the study of the composition and properties of matter Chemists interested in: 1) composition and structure of substances 2) the properties of these substances 3) the conditions under which these substances change to form new ones

3. B. History of Chemistry 1) Began with the Greeks - Democritus 2) Alchemists 3) Modern Chemistry Begins

4. C. Models of the Atom 1) Greeks (Democritus) – 400 B.C. 2) Dalton – 1803 A small particle with several smaller pieces within.

5. 3) Thompson – 1898 The Plum Pudding Model 4) Rutherford – 1911 Concentric Rings

6. 5) Bohr – 1923

7. 6) Scroedinger – Present Based on the probability of where electrons would be found about the nucleus.

8. D. Subatomic Particles We are interested in three particles and their mass, charge, and location. AMU – Atomic Mass Unit

9. In an atom/element the number of protons is always equal to the number of electrons. • We always round the atomic mass to the nearest whole number. # Neutrons = Atomic Mass - Atomic Number

10. Atomic Number – Tells us the number of protons 16 S Sulfur 32.06 Element Symbol Element Name Atomic Mass – tells us the number of neutrons and protons

11. E. Ions • ions are formed when an electron is either gained or lost. • when an electron is gained, it becomes a negative ion and we call this an anion. • when an electron is lost, it becomes a positive ion and we call this a cation.

12. When naming a cation, simply add the word 'ion' to the end of the element name. Ex// Mg - Magnesium  Mg+2 - Magnesium ion Ca - Calcium  Ca+2 - Calcium ion Na - Sodium  Na+1 - Sodium ion

13. When naming an anion, drop the last few letters of the element name and add the ending -ide. Ex// O - Oxygen  O-2 – Oxide N – Nitrogen  N-3 - Nitride Cl - Chlorine  Cl-1 – Chloride • ions become charged because they want 8 electrons in their outer shell (octet)

14. When an anion and a cation come together, they form a compound.

15. F. Compounds (Ionic) Compounds are a combination of two or more elements • when an atom loses an electron, it becomes positive which is known as a cation. • when an atom gains an electron, it becomes negative which is known as an anion. • Cations and anions are attracted to each other and thus come together to form a compound.

16. Compounds must be balanced so that the positive charges balance the negative charges. • Compounds must also be written in lowest possible form.

17. NAMING • the cation always goes first, followed by the anion. • use the element name for the cation. • use the ion name for the anion. 1. a) Li+1 P-3 b) Mg+2 F-1 c) Ca+2 N-3 d) Cu+2 O-2 e) Cr+3 S-2 f) Fe+2 S-2 g) Ag+1 S-2 h) Al+3 Br-1 i) Fe+3 O-2

19. 2. Write the chemical formula for each of the following compounds. • Potassium chloride • Calcium nitride • Copper (II) oxide • Iron (III) bromide • Magnesium phosphide • Aluminum selenide • Chromium (III) sulfide • Tin (II) oxide

20. 3. Name each of the following compounds. a) Li2O b) Ag3N c) SnO2 d) CrCl3 e) BaS f) Fe2O3 g) Cu3P h) V2O5

21. G. Writing Equations Products - are the chemicals that are made or produced in a chemical reaction Reactants - are the chemicals that begin or go into the reaction before it takes place

22. Chemical Reaction - when the chemicals that go into the reaction change and new products (chemicals) are formed. Ex. MgI2 + Na2O  NaI + MgO Reactants Products When we write the compounds, we must make sure that they are balanced.

23. ‘+’ – tells us that two compounds are combining. Key Words – combines, mixes, reacts, and, etc. ‘’ – acts as an equals sign to separate reactants and products. Key Words – to form, to produce, to make, synthesize, decompose, break down, etc.

24. Sample Problems 1) Magnesium bromide reacts with calcium nitride to form magnesium nitride and calcium bromide. 2) Copper (II) oxide reacts with lithium phosphide and produces copper (II) phosphide and lithium oxide.

25. 3) Tin (IV) sulfide reacts with calcium iodide and makes tin (IV) iodide and calcium sulfide. 4) Lithium chloride decomposed to form lithium and chlorine. Magic Seven – if ever the following elements are by themselves, they are found in pairs (diatomic). N2, O2, F2, Cl2, Br2, I2, At2, H2

26. 5) Calcium reacts with iodine to form calcium iodide. 6) Chromium (III) iodide combines with sodium phosphide to make chromium (III) phosphide and sodium iodide.

27. H. Writing Word Equations Examples 1) CaI2 + Al2O3 CaO + AlI3

28. 2) CrI2 + Cu2S  CrS + CuI 3) Fe2O3 + KF  FeF3 + K2O

29. I. Acids and Bases

30. Acids • Have a sour taste • Very corrosive • Neutralize bases • Conduct electricity very well • Dissolve in water to produce hydrogen ions (H+) in solution • When an acid and a base neutralize each other, they form salt and water NaOH + HCl  H2O + NaCl Sodium Hydrochloric Water Salt Hydroxide Acid

31. Bases • Have a bitter taste • Very corrosive • Neutralize acids • Conduct electricity very well • Dissolve in water to produce hydroxide ions (OH-) in solution • When an acid and a base neutralize each other, they form salt and water

32. Acid-Base Indicators • Acid – Base indicators are substances that change different colors when added to acids and bases. • Litmus Paper – red in an acid - blue in a base • Bromothymol Blue – yellow in an acid - blue in a base

33. pH paper – is another type of indicator that can change to several different colours to tell the scientist how acidic or basic the solution is.

34. pH Scale • An acid-base indicator will not tell you how acidic or basic a solution is. • The pH scale indicates the level of acidity of a solution and it ranges from 0-14. • pH of 0-6.9 is acidic. • pH of 7 is neutral. • pH of 7.1-14 is basic. • The pH scale is logarithmic (based on the power of ten). This means the difference between a pH of 5 and 6 is actually ten times. The difference between 4 and 6 is actually 100 times.

35. Maintaining a constant pH is often very important for biological systems. • Human blood has a pH range of 7.35-7.45. Any change from this could be fatal. • Plants grow best in soil with a pH between 6 and 7. Any higher or lower, prevents the plants from absorbing nutrients. • Shampoo normally has a pH of about 8. The human scalp has a pH of about 6. A scalp that becomes too basic results in dandruff.

37. THE END Exam Time!