Presentation on theme: "The Atom and the Periodic Table"— Presentation transcript:
1 The Atom and the Periodic Table ChemistryThe Atom and the Periodic Table
2 A Picture of an Atom Most of an atom is empty space! The nucleus contains most of the mass of the atomThe # of protons = the # of electrons (in a neutral atom)The # of protons determines which element the atom isThe number of neutrons can change – this is called an isotopeSome elements can lose an electron(s) (become positively charged) or gain an electron(s) (become negatively charged) – charged atoms are called ions
9 Electrons are placed in specific electron shells Electrons are placed in specific electron shells. Each period number equals the number of electron shells in the atom, which stays the same for all the elements in each period
10 Elements in a group or family have similar properties (characteristics) and undergo the same type of chemical reactions (due to having the same number of valance electrons)Elements across a period change in a regular way (the # of protons increases as does the #of electrons and the atomic mass), but the number of electron shells stays the same
12 All Pure Matter has Physical Characteristics Can observe without changing into a new substanceExamples: boiling point, freezing/melting point, hardness, color, texture, & state at room temperature (gas, liquid or solid), density, solubility (if possible) in water or non-polar solventIf a metal: luster, malleability, conductivity of electricity and heat, attraction to magnet
13 If matter undergoes a physical change, then it is the same substance with the same physical and chemical properties
14 Example: an ice cube, liquid from the faucet, and steam from a boiling pot are all water. Each state has the same chemical formula, freezing/melting and boiling points, clear color, and is the universal solvent.
15 All Pure Matter has Chemical Characteristics Can’t be observed just by looking at itDescribes ability to turn into a new substanceTo observe the property, the substance MUST react with another and form other pure substance(s), SO there must be a chemical reactionExamples: flammability, reacts with gas (iron to form rust, copper turns green, silver tarnishes), reacts with metals (acids)
16 If matter undergoes a chemical reaction, there is a new substance with its own physical & chemical properties
17 Sodium (Na) - soft, silvery metal that explodes in water Chlorine (Cl) - a poisonous yellow-green gas.
18 Chemical Reaction: sodium chloride (NaCl) a white soliddissolves in water without explodingsafe to eat – table saltmelting point of 801°C (Na 97.85°C)boiling point of 1413°C (Cl -34.6°C).
20 Compounds vs. MixturesA compound is a pure substance made of 2 or more atoms (molecule) that reacted chemically and has unique chemical properties of its own.A mixture is made of 2 or more substances that do no react chemically, and retain their chemical properties.
21 Types of MixturesHeterogeneous – no matter how well mixed, you can still see the separate partsExample – salad: lettuce, tomatoes, croutons, etc.; can pick out the cucumber slices if you don’t likeHomogeneous – parts are so evenly mixed, you can’t see the different parts; looks like one substanceExample – teaspoon of sugar stirred into hot tea; can’t see sugar but the tea tastes sweet.
22 What is another name for homogeneous mixture? Solution – a well-mixed mixtureAt least one substance dissolves into anotherSolute – substance dissolved into the 2nd substance (smaller amount)Solvent – substance that surrounds the 1st substance (larger amount)Solubility is a measure of how much solute goes into solvent at a given temperature – this is a physical property
24 Are all solutions a solid dissolving into a liquid? Liquid into liquidGas into gasGas into liquidSolid into solidAnti-freeze: ethylene glycol into waterOxygen in airOxygen in water, CO2 in soda waterAlloys: metal in metal such as bronze (Sn in Cu), brass (Zn in Cu), 14 kt gold (Ag, Cu, or Zn in Au)
25 Factors That Affect Solubility TemperaturePressureSolvent compatibility
26 Temperature Affects Solubility ↑ solid’s solubility by ↑ temperature, genetallygenerally
28 Pressure Affects Solubility ↑ gas’ solubility by ↑ pressure over the solvent
29 Solvent Compatibility - Like Dissolves Like Polar solvent + ionic compoundWater is a polar molecule: (+) & (-) sidesSalt is an ionic compoundThe sodium ion (Na+) is attracted to water’s (-) sideThe chlorine ion (Cl-) is attracted to water’s (+) side.
30 Polar Solvent + Polar Solute Polar ammonia molecules dissolve in polar water molecules.The +H of the water molecule is attracted to the –N of the ammonia molecule AND…The +H of the ammonia molecule is attracted to the –O of the water molecule
31 Non-polar + non-polar Even if a substance is soluble, it may not dissolve in waterNon-polar: no (+) & (-) parts of moleculeAcetone is a solvent that is partially polarThe components in nail polish are non-polarchemicals (resins) dissolved in acetoneLetting your nails dry means allowing the solvent to evaporate leaving the resin behind.To remove, the polish needs to dissolveThis is the same reason you can’t clean oil-based paint from a paint brush using water. You must use turpentine.- -
39 Indicator paper call tell you if a substance isacid (< 7), base (> 7)or neutral (= 7)The closer to 0, thestronger the acidThe closer to 14, thestronger the base (ormore alkaline)The closer to 7, theweaker the acid or baseStrength determines safety
40 What Happens If An Acid & Base Mix? Neutralization = reaction between acid and baseResulting substance is less acidic, less basic than the original substancesacid + base = a salt + waterHow close to pH 7 depends on the concentrations and amounts of the originals