Chapter One Atoms and Elements

Transcription

1 S u m m e r S c h l S c i e n c e S T P a g e 1 Chapter One Atms and Elements Histry f the Atm Daltn s Atmic Mdel Daltn thught f atms as slid, indivisible balls f different Thmsn s Atmic Mdel Thmsn viewed the atm as a bdy like a, with a certain amunt f muffin dugh (psitively charged substance) embedded with blueberries (negatively charged particles; electrns) Rutherfrd s Atmic Mdel A small, dense is entirely psitive with negatively charged electrns scattered randmly arund the nucleus Rutherfrd-Bhr Atmic Mdel The atm cntains a very small nucleus surrunded by electrns mving in (r electrn shells) Simplified Atmic Mdel Chadwick added the t the Rutherfrd-Bhr mdel. Parts f the Atm Nucleus: Center f the atm Prtn: Charged, Lcated in the Nucleus Neutrn: Has n electrical charge, is n. Lcated in the nucleus Electrns: Charged, Travel arund the Nucleus n Electrn Orbits r Electrn Shells

2 S u m m e r S c h l S c i e n c e S T P a g e 2 The Peridic Table f Elements The Peridic Table f Elements is a visual presentatin f the elements in grups accrding t their physical and chemical prperties. are fund t the left f the staircase. Metals are generally gd cnductrs f electricity and heat. are t the right f the staircase, except Hydrgen. Nn-metals are generally pr cnductrs f electricity and heat. are fund alng bth sides f the staircase. Metallids have prperties f bth metals and nn-metals. They include, Brn, Silicn, Germanium, Arsenic, Antimny, Tellurium, Astatine Grups (Clumns ): The grup # is hw many an element has. Grup 1 - Alkali Metals: Sft, highly reactive metals. Never fund in their elemental state in nature, instead they are in the frm f cmpunds. Grup 2 Alkaline Earth Metals: Highly malleable and reactive, and they burn easily in the presence f heat. They are nt fund in their elemental state in nature either but can be expsed t air. Grup 7 Halgens: They are nn-metals that react easily t frm cmpunds including salts. Grup 8 Nble Gases (als called rare r inert gases): They are very stable because they have full valence electrn shells. They can be fund in their elemental state in nature. Perids (Rws ): The perid # is hw many an element has. Representing Atms The atmic number represents the number f prtns in the nucleus f an atm. When dealing with the first 20 elements f the peridic table, the fllwing rules apply: Electrns fill the shells clsest t the nucleus befre ccupying a farther shell The first shell (the ne clsest t the nucleus) can cntain a maximum f tw electrn shells. The secnd shell can cntain a maximum f eight electrns. The third and furth shells als cntain a maximum f eight electrns.

3 S u m m e r S c h l S c i e n c e S T P a g e 3 Lewis Ntatin Atmic Mdel Lewis Ntatin is a way f representing atms using nly their valence electrns (valence electrns are electrns in the utermst shell f an atm). Hw? Step 1: Write dwn the symbl fr the element. Step 2: Lk at the grup number (clumn number) t see hw many valence electrns the element has. Step 3: Fill in the valence electrns, placing ne at a time arund the symbl, like the fur pints n a cmpass and starting with the right side. Once all fur psitins are filled, the electrns are then dubled t frm pairs. Nitrgen: Chlrine: Sdium: Brn: Argn: Carbn: Rutherfrd-Bhr Atmic Mdel This methd f representing atms shws the number f electrn shells as well as the number f prtns and electrns. Hw? Step 1: Draw the nucleus with the number f prtns (which is the same as the atmic number). Step 2: Lk at the perid t see hw many electrn shells the element has. Step 3: Fill in yur electrns (the first shell is full with tw electrns, all ther shells are full with eight electrns)

4 S u m m e r S c h l S c i e n c e S T P a g e 4 Oxygen: Brn: Magnesium: The Ball-and-Stick Atmic Mdel In this mdel, the atm is depicted as a ball, and its bnds with ther atms are shwn with sticks. The size f the ball is generally prprtinal t the number f electrn shells in the atm. Ex:

5 S u m m e r S c h l S c i e n c e S T P a g e 5 Chapter Tw Mlecules and Slutins An atm is the particle f matter. It cannt be divided chemically. Examples include: Oxygen, Calcium etc. A mlecule is a grup f. Examples include H 2 O (water) r NaCl (table salt) Why d atms tend t bnd with ther atms? One reasn is t acquire an electrn cnfiguratin similar t that f the nble gases (t have ). T d this, atms must gain r lse electrns. An in is an atm that has becme electrically charged by lsing r gaining ne r mre.. Example: Flurine: 9p+ What des Flurine have t d t becme stable? Flurine can gain ne electrn. 2e 7e F befre (as an atm) F after (as an in) Prtns: Prtns: Electrns: + Electrns: + F -1 ( atm) ( In) *The number f prtns in an atm never changes (lk at the atmic number) Catins Psitive Charge Have lst electrns Anins Negative Charge Have gained electrns

6 S u m m e r S c h l S c i e n c e S T P a g e 6 Slutins A mixture is when atms cmbine tgether, but nt chemically. Ex: If yu put sand in a glass f water, the sand sinks t the bttm. The sand-water cmbinatin is a mixture. A slutin is a grup f mlecules that are mixed up in a cmpletely even distributin. Ex: If yu put sugar in a glass f water, the sugar disslves and is spread thrughut the glass f water. The sugar-water cmbinatin is a slutin. The slute is what is placed in the slvent. The slvent is what disslves the slute. Ex: The is the slute. The is the slvent Slubility is the amunt f slute (ex: sugar) that can be disslved by the slvent (ex: water). Cncentratin f a slutin is the amunt f slute in a given amunt f slutin. A higher cncentratin means f slute (ex: a lt f chicken brth pwder in yur sup). A lwer cncentratin means slute (ex: a small amunt f chicken brth pwder in yur sup). Remember that the amunt f slvent can als affect the cncentratin (less slvent means a lwer cncentratin, mre slvent means a higher cncentratin). Change Additin f Slvent (Dilutin) Additin f Slute (Disslutin) Reductin f Slvent (Evapratin) Effect n the cncentratin Reduced cncentratin Increased cncentratin Increased cncentratin

7 S u m m e r S c h l S c i e n c e S T P a g e 7 The fllwing frmula can be used t calculate cncentratin in g/l where C is the cncentratin (in ) M is the mass f the slute (in ) V is the vlume f the slutin (in ) 1. Yu are given 30 g f salt and tld t make a slutin f 500ml. What will the cncentratin f the slutin be? 2. It s a ht day and yu want t make sme iced tea. Yu want t make a full glass (250 ml) and the cncentratin shuld be 16 g/l. Hw much iced tea pwder wuld yu need? Yu may als be asked t find cncentratin in percent. 1. What is the cncentratin percent (m/v) f 400 g f slute in 2.8 L f water? Cncentratin can als be fund in PPM (parts per millin) 1ppm = 1. A 30 L sample f river water has 12 g f cntaminant in it. What is the PPM cncentratin f the pnd water?

8 S u m m e r S c h l S c i e n c e S T P a g e 8 Electrical Cnductivity - An aqueus slutin is a slutin in which the slvent is (ex: a water-sugar slutin is called an aqueus slutin) Electrlytes - An electrlyte is a substance that, when disslved in water an electric current t flw thrugh the slutin. Types f Electrlytes Acids - Example: fruit juice, sft drinks and gastric juices secreted by the human stmach - Often has a sur taste - Acids have a PH level less than 7 - Often begins with H - Turns litmus paper red Bases - Fund in many cleaning prducts - Often has a bitter taste - Bases have a PH level mre than 7 - Often ends with OH - Turns litmus paper blue Salts - Very large class f substances (ften in the human diet) - Desn t cntain H atms - Made up f a metal and a nn-metal Classify the fllwing electrlytes as an acid, base r salt: a) NaOH : i) PH level f 6.9: b) H 2 SO 4 : j) PH level f 12: c) NH 4 OH : k) PH level f 3.4: d) NaCl : l) PH level f 7.1: e) HCl : m) PH level f 1.7: f) MgOH : n) PH level f 7:

9 S u m m e r S c h l S c i e n c e S T P a g e 9 PH Scale - We use the PH scale t determine whether substances are acids, neutrals r bases. The PH scale ranges frm 0 t A PH level less than 7 means it is an, a PH level f 7 means it is and a PH level greater than 7 means it is a. The difference f ne unit between tw substances actually shws that ne substance is 10 times mre acidic than the ther. Fr example, a slutin with a ph f 3 is times mre acidic than a slutin with a ph f 4. A slutin with a ph f 9 is times less basic than a slutin with a ph f 11. Label each f the fllwing as an acid, a base, a salt r neutral. a) NaOH i) Lemn juice: b) Baking Sda: j) Mg(OH) 2 : c) NaCl: k) CaCl 2 : d) Battery Acid: l) Distilled Water: e) Slutin with a ph f 6: m) Slutin with a ph f 2: f) AgNO 3 : n) H 2 SO 4 : g) Slutin with a ph f 13.9: ) Slutin with a ph f 7: h) Sap: p) Ammnia:

10 S u m m e r S c h l S c i e n c e S T P a g e 10 Chapter Three - Different frms f energy Energy is the ability t r. Frms f Energy Frm f energy Descriptin Surces Energy stres in an bject due t its Cmpressed spring cmpressin r extensin Energy frm the rdered mvement f electrns Pwer plant, battery, generatr Energy frm the randm mtin f all particles in a substance Fire, heating element, sun Energy cntained in and transprted by electrmagnetic waves Light bulb, micrwaves, cell phnes Energy stred in mlecular bnds (chemically bnded atms) Apple, Candlewax, Fssil fuels Energy frm the mvement f air Wind Energy cntained in and transprted by sund waves Sund, music Energy frm the flw f water Waterfall, river Energy stred in atmic nuclei Atmic nuclei, sun Thermal Energy is the energy cntained in a substance, determined by the number f particles in the substance and their temperature. Heat is the transfer f thermal energy between tw envirnments with different temperatures. Heat always passes frm the warmer t the cler envirnment. Temperature is a measure f the degree f agitatin f the particles in a substance.

11 S u m m e r S c h l S c i e n c e S T P a g e 11 The Law f Cnservatin f Energy Energy cannt be, and energy cannt be. Energy can nly be transferred (the mvement f energy frm ne place t anther), r transfrmed (the changing f energy frm ne frm t anther). Due t the law f cnservatin f energy, the ttal amunt f energy in an islated system always remains cnstant. Energy efficiency is the percentage f energy cnsumed by a machine r system that was transfrmed int useful energy. Example: T perfrm wrk equal t J, a machine cnsumes J. What is the energy efficiency f this machine?

12 S u m m e r S c h l S c i e n c e S T P a g e 12 Chapter Fur Changes in Matter A physical change desn t change the nature r characteristic prperties f matter. The atms and mlecules f the substance. Examples f physical changes; snw melting in the sun, trees being cut dwn. A chemical change alters the nature and characteristic prperties f matter. The bnds between atms are rearranged and are frmed. Examples f chemical changes; paper burning. The fllwing are signs that pint twards a chemical change having ccurred The release f a gas The emissin r absrptin f heat The emissin f light A change in clur The frmatin f a precipitate The Law f Cnservatin f Mass The ttal mass f reactants is always t the ttal mass f prducts.

13 S u m m e r S c h l S c i e n c e S T P a g e 13 Balancing Chemical Equatins Remember yur steps: 1. Separate the tw sides. 2. Make a list f all elements (every element starts with a capital letter) 3. Hw many f each element are already present? 4. Start adding cefficients (number in frnt f an element) t try t balance ne element at a time. 5. G back and frth between the tw sides t balance ne element at a time. 6. Check yur answer! Als remember that H 2 r 1 H 2 r just H 2 all mean the same thing. N cefficient = the same as a 1. Practice! 1. H2 + O2 H2O 2. N2 + H2 NH3 3. S8 + O2 SO3

14 S u m m e r S c h l S c i e n c e S T P a g e 14 Types f Chemical Changes Acid-Base Neutralizatin: A chemical change invlving the reactin f an acid with a base, prducing a salt and water. Example: HCl + NaOH NaCl + H 2 O Oxidatin: A chemical change invlving r a substance with prperties similar t thse f xygen. Example: Humidity in the air accelerates the frmatin f rust. Cmbustin: A frm f xidatin that releases a large amunt f. Three cnditins must be fulfilled fr cmbustin t ccur: - An xidizing agent ( ) is needed - A fuel is needed (Wd and prpane are excellent fuels) - Ignitin Temperature is the minimum temperature needed t start cmbustin, it changes frm ne fuel t anther. Cmbustin Types: Rapid Cmbustin releases a great deal f energy in a shrt amunt f time. Examples: a lg fire, burning candle Spntaneus Cmbustin rapid cmbustin in which the fuel reaches its ignitin temperature withut any energy frm an utside surce. Examples: When it is very ht and dry in the summer, wd can catch fire spntaneusly. Slw Cmbustin ccurs ver a very lng perid f time. Examples: decmpsitin, cellular respiratin, metal crrsin Cellular Respiratin: A chemical change in which glucse and xygen generates energy and prduces carbn dixide and water Sugar + Oxygen -> Energy + Carbn Dixide + Water Phtsynthesis: A chemical change that prduces glucse and xygen frm slar energy, carbn dixide and water. Slar energy + Carbn Dixide + Water -> Sugar + Oxygen

15 S u m m e r S c h l S c i e n c e S T P a g e 15 Chapter Five Electricity and Magnetism Electricity describes all phenmena caused by charges. Electrical charge is a prperty f prtns and electrns. A prtn carries a psitive charge while an electrn carries a negative charge. A charged bdy has mre electrns than prtns. A charged bdy has mre prtns than electrns. Electrical Frces Electrical charges f like signs (tw psitive r tw negative) each ther. Electrical charges f ppsite signs (a negative and a psitive) each ther. allw the free flw f electrical charges (ex: metals and electrlytic slutins) hinder the free flw f electrical charges (ex: nn-metals are usually insulatrs, and substances such as wd, plastic, glass, paper). Circuits An electrical circuit is a netwrk in which electrical charges can flw cntinuusly in a lp. If the electrical charges cannt flw cntinuusly in a lp the circuit will nt wrk. Circuits need the fllwing cmpnents t wrk: A pwer supply: creates a ptential difference (ex: ) Electrical resistance: Smething that uses electrical energy (ex: ) Wires: carries the charges frm the pwer supply t the elements and then back t the pwer supply.

16 S u m m e r S c h l S c i e n c e S T P a g e 16 Symbls in a circuit One battery: Lightbulb: Vltmeter: Switch (n psitin): Tw batteries: Resistr: Ammeter: Switch (ff psitin): Cnventinal Current Directin is frm the psitive terminal f the pwer supply t the negative terminal. + t - Electrns actually flw frm the negative terminal f the pwer supply t the psitive. t + terminal. Series Circuit A circuit where the cmpnents are cnnected end t end (in ). - Electrns have ne path t fllw (frm negative t psitive) - If ne light bulb burns ut, n ther light bulbs in a series circuit will wrk. Parallel Circuit A circuit that branches ut at least nce (r has ). - Electrns have multiple paths t fllw - If ne light bulb burns ut, the thers can still wrk

17 S u m m e r S c h l S c i e n c e S T P a g e 17 Ammeters measure the current intensity travelling thrugh a circuit. They can be placed within the lp f a circuit. Vltmeters measure the ptential difference f a circuit element (such as a mtr r light bulb). They need t be placed ut f. Ohm s Law V=RI Where V is the ptential difference (in ) R is the resistance (in ) I is the current intensity (in ) Electrical Pwer P = VI Where P is electrical pwer (in ) V is the ptential difference (in ) I is the current intensity (in ) Energy Cnsumed E = P t Where E is energy cnsumed (in ) P is electrical pwer (in ) is time difference (in ) Energy Cnsumed (E) can als be in watt-hur if electrical pwer (P) is in watts and time (t) is in hurs. Or Energy Cnsumed (E) can als be in kilwatt-hur if electrical pwer (P) in kilwatts and time (t) is in hurs

18 S u m m e r S c h l S c i e n c e S T P a g e 18 Hw t cnvert: x K H DA U D C M Magnetism All magnets have a and a. These are frmed when electrns f a magnet rtate in the same directin. Electrns in nn-magnetized bjects rtate in ppsite directins. Magnetic Fields A magnet s frce affects a limited area arund the magnet. This area is called the magnetic field. The magnetic field has lines which pint OUT OF NORTH and INTO THE SOUTH

19 S u m m e r S c h l S c i e n c e S T P a g e 19 Cmpass A cmpass cntains a small magnet with a Nrth Ple and a Suth Ple. When a cmpass is placed next t anther magnet, the cmpass NORTH POLE will pint t the SOUTH POLE f the ther magnet, and the SOUTH POLE will pint t the NORTH POLE alng the magnetic lines.