Chemistry

1. Chemistry

2. Physical Properties • Properties of matter that can be observed or measured without changing the identity of the matter • Ex. • Color, Smell, Mass, Volume, Density • Conductivity (ability to transfer energy) • State {physical form (solid, liquid, gas)} • Malleability (ability to be hammered into thin sheets) • Ductility (ability to be drawn into a wire) • Solubility (ability to dissolve in another substance)

3. Chemical Properties • Chemical Properties: describe a substance based on its ability to change into a new substance with different properties • Ex. Flammability, reactivity • Metal reacts with oxygen to form rust.

4. Physical changes • A change that affects one or more physical properties of a substance, but doesn’t change its chemical identity. • Ex: breaking a pencil, melting, dissolving sugar in water, cutting your hair, crushing an aluminum can

5. Physical changes • An easy way to tell if something is a physical change, is to determine if it can be undone. • Ex: • Ice cubes that melt in a bowl can be refrozen. • A broken pencil still writes. • Hair doesn’t turn into something else when it’s cut.

6. Chemical Change • A change that occurs when one or more substances are changed into entirely new substances with different physical properties. • Ex. Baking a cake, effervescent tablets fizzing in water, a car rusting

7. States of Matter • There are four states of matter: solid, liquid, gas, and plasma • Matter is in constant motion.

8. Pure Substance • Pure substances are made of only one type of particle. • Elements: A pure substance that cannot be separated into simpler substances by physical or chemical means. • Ex. Carbon (C), Oxygen (O), Gold (Au) • Represented by 1 or 2 letters, first letter always capital • Each element has unique physical and chemical properties that can be used to identify them. • For the most part…elements can be divided into three categories.

9. Elements Metals Nonmetals Metalloids Pure substances: Elements

10. Pure substances: Elements • Metals: Shiny, good conductors of electricity, malleable, ductile • Ex. Iron, Copper • Nonmetals: Dull, poor conductors of electricity, brittle and unmalleable • Ex. Sulfur, Neon • Metalloids: Semiconductors of electricity, somewhat malleable and ductile, some shiny some dull • Ex. Boron, Silicon

11. Periodic Table

12. Pure Substance: Compounds • Compounds: A pure substance that is composed of two or more elements that are chemical combined. • Have a fixed ratio of elements. • When compounds form they take on new characteristics. • Ex. Na + Cl → NaCl or 2H2 + O2 → 2H2O

13. Common Compounds • NaCl: Sodium Chloride (Table Salt) • H2O: Dihydrogen Monoxide (Water) • CO2: Carbon Dioxide • CH4: Methane • C6H12O6: Glucose (Sugar)

14. Pure Substance: Compounds • Since compounds are composed of elements that are chemical combined, they must undergo chemical changes to be broken down into the constituent elements. • Most of the substances that we deal with everyday are compounds, because most elements are too reactive to remain as a single element. • Ex: Proteins, CO2, NH4

15. Mixtures • A mixture is a combination of two or more substances that are NOT chemically combined. • Ex. Pizza, Salt water • Mixtures can be separated by physical means. (filtration, centrifuge, evaporation, mechanical separation, magnetism) • Do not have fixed ratios.

16. Mixtures :Solutions • Homogenous (solution): Particles are uniform throughout • Examples: Salt water, alloy (metals dissolved in metals) Brass=zinc+copper • Solute: substance that is dissolved • Ex: Salt • Solvent: substances that is doing the dissolving • Ex. Water (Universal Solvent!)

17. Mixtures :Solutions • Solubility: basically how much of the solute can be completely dissolved by the solvent • Increases with: • Temperature (except with gases) • Surface Area • Stirring

18. Atoms • An atom is the smallest particle into which an element can be divided and still be the same substance. (Building block of matter) • Composed of… • Protons • Neutrons • Electrons

19. Atoms

20. Atoms • Atomic number: tells the number of protons • Mass number: # protons + # neutrons • Atomic mass: average of the masses of the existing isotopes in an element • Isotopes: Elements that have the same # of protons, but a different # of neutrons • Some isotopes are radioactive (carbon dating) • Naming: Isotopes are named for the element and then the atomic mass (Carbon-14)

21. Practice • Determine the number of protons, neutrons, and electrons in the following: • Potassium (K) • Oxygen (O) • Sodium (Na) • Helium-3 (3He)

22. Ions • Atoms that have either gained or lost one or more electrons. Therefore they have either a positive or negative charge. • Cation: (+) Positive charge • Anion: (-) Negative charge

23. Atoms: Electrons • Electrons orbit the nucleus of the atom. • For the Bohr model electrons are placed in orbitals by the formula 2n2, where n=energy level • So for the first energy level: 2(1)2=2 • The second energy level: 2(2)2=8 • The third energy level: 2(3)2=18

24. Reactivity • All elements want to achieve noble gas configuration. • They will donate or accept electrons to achieve this configuration. • The most reactive elements are very close to achieving noble gas configuration and they readily achieve it! • Ideally they want 8 electrons in their outer shell! • Valance Electrons: outer electrons

25. The Periodic Table

26. Why is the Periodic Table important to me? • The periodic table is the most useful tool to a chemist. • You get to use it on every test. • It organizes lots of information about all the known elements.

27. Pre-Periodic Table Chemistry … • …was a mess!!! • No organization of elements. • Imagine going to a grocery store with no organization!! • Difficult to find information. • Chemistry didn’t make sense.

28. HOW HIS WORKED… Put elements in rows by increasing atomic weight. Put elements in columns by the way they reacted. SOME PROBLEMS… He left blank spaces for what he said were undiscovered elements. (Turned out he was right!) He broke the pattern of increasing atomic weight to keep similar reacting elements together. Dmitri Mendeleev: Father of the Table

29. The Current Periodic Table • Mendeleev wasn’t too far off. • Now the elements are put in rows by increasing ATOMIC NUMBER!! • The horizontal rows are called periods and are labeled from 1 to 7. Periods tell the number of energy levels the atom has. • The vertical columns are called groups are labeled from 1 to 18.

30. Groups…Here’s Where the Periodic Table Gets Useful!! • Elements in the same group have similar chemical and physical properties!! • (Mendeleev did that on purpose.) Why?? • They have the same number of valence electrons. • They will form the same kinds of ions.

31. Families on the Periodic Table • Columns are also grouped into families or groups. • Families may be one column, or several columns put together. • Families have names rather than numbers. (Just like your family has a common last name.)

32. Hydrogen • Hydrogen belongs to a family of its own. • Hydrogen is a diatomic, reactive gas. • (Br, I, N, Cl, H, O, F) • Hydrogen was involved in the explosion of the Hindenberg. • Hydrogen is promising as an alternative fuel source for automobiles

33. Alkali Metals • 1st column on the periodic table (Group 1) not including hydrogen. • Very reactive metals, always combined with something else in nature (like in salt). • Soft enough to cut with a butter knife • 1 electron in outer orbital

34. Alkaline Earth Metals • Second column on the periodic table. (Group 2) • Reactive metals that are usually combined with nonmetals in nature. • Not as reactive as alkali metals. • Several of these elements are important mineral nutrients (such as Mg and Ca) • 2 electrons in outer shell

35. Transition Metals • Elements in groups 3-12 • Less reactive harder metals • Includes metals used in jewelry and construction. • Metals used “as metal.” • Higher densities and melting points than groups 1 and 2.

36. Lanthanides and Actinides • Transition metals placed here to keep periodic table from being too wide. • Named for the elements that they follow. • Lanthanides: • Shiny, reactive metals, used in steel manufacturing • Actinides: • Radioactive (unstable) • Synthetic past U!

37. Boron Family/Group • Elements in group 13 • Aluminum metal was once rare and expensive, not a “disposable metal.” • Contains 1 metalloid and 4 metals • 3 electrons in outer level • Solid at room temperature

38. Carbon Family/Group • Elements in group 14 • Contains elements important to life and computers. • Carbon is the basis for an entire branch of chemistry. • Silicon and Germanium are important semiconductors. • 4 electrons in outer shell

39. Nitrogen Family • Elements in group 15 • Nitrogen makes up over ¾ of the atmosphere. • Nitrogen and phosphorus are both important in living things. • The red stuff on the tip of matches is phosphorus. • 5 electrons in outer shell

40. Oxygen Family/Group • Elements in group 16 • Oxygen is necessary for respiration. • Many things that stink, contain sulfur (rotten eggs, garlic, skunks,etc.) • 6 outer electrons

41. Halogens • Elements in group 17 • Very reactive, volatile, diatomic, nonmetals • Always found combined with other element in nature . • Used as disinfectants and to strengthen teeth. • 7 outer electrons

42. The Noble Gases • Elements in group 18 • VERY unreactive, monatomic gases • Used in lighted “neon” signs • Used in blimps to fix the Hindenberg problem. • Have a full valence shell.

44. Reactivity • Noble Gases are at the far right of the periodic table. • Reactivity increases as you go to the left and the top of the periodic table.

45. Chemical Bonding A chemical bond is the force of attraction that holds two atoms together. The key to bonding is found in the number of valance electrons. Valance electrons: electrons that are in the outermost energy level of an atom Remember the goal is to have 8 valance electrons (exception H and He)

46. Chemical Bonding • The oxidation number of an atom is the charge that atom would have if the compound was composed of ions.

47. Bonding: Ionic, Covalent, Metallic Ionic bond: forms between a metal and a nonmetal where the metal gives up an electron to the nonmetal and the resulting oppositely charged ions attract each other.

48. Bonding: Ionic, Covalent, Metallic Covalent bond: involves the sharing of electrons between atoms Can exist as a single, double, or triple bond (C, O, N)

49. Bonding: Ionic, Covalent, Metallic Metallic bond: gives metals their unique characteristics due to delocalized electrons that can flow throughout the metal Occurs in transition metals.

50. Predicting bonding First determine how many e- are in the atoms outer shell. Next determine whether it is likely to lose or gain e- or if it is able to share e-. Ionic=nonmetal+metal Covalent = nonmetal + nonmetal