The Periodic Table & Atomic Structure The periodic table is an arrangement of the known elements. The modern periodic table has the elements arranged in order of increasing atomic number…….the early versions had the elements arranged according to atomic mass. Can you find examples where this would be different to the modern version? The periodic table briefly Independently arrived at by Mendeleev and Meyer in the mid-19th century. Mendeleev predicted the properties of undiscovered elements and left spaces in his periodic table. Consists of a series of horizontal rows, periods and vertical columns, groups: Group 1: Alkali metals Group 2: Alkaline earth metals Group 7: Halogens Group 8: Inert gases provides a summary of atomic weights and numbers, symbols and names for the elements understanding of properties of related elements Chemical Formulae A chemical symbol represents one atom of an element. A chemical formula represents one molecule or one formula unit of an element or compound The formula shows: Each type of atom present The number of each atom present in the molecule or formula unit Coefficients, superscripts and subscripts where necessary A molecule is a group of atoms which are bonded together…the atoms may be the same or different. Examples: Elements Compounds H2 = hydrogen H2O = water P4 = phosphorus C6H12O6 = glucose O2 = oxygen NH3 = ammonia A formula unit represents the simplest ratio of atoms in a substance, which may be a giant lattice
potassium K+ calcium Ca2+ iron (III) Fe3+ tin (IV) Sn4+ bromide Br - chromate CrO42- Phosphide P3- silver Ag+ Copper (II) Cu2+ chlorate ClO3 - dichromate Cr2O72- Nitride N3- sodium Na+ iron (II) Fe2+ chloride Cl - oxide O2- Hydrogen H+ lead (II) Pb2+ fluoride F - peroxide O22- magnesium Mg2+ hydrogen carbonate HCO3- sulfate SO42- mercury(II) Hg2+ hydrogen sulfate HSO4 - sulfite SO32- nickel Ni2+ hydroxide OH - sulfide S2- tin (II) Sn2+ iodide I - nitrate NO3 - nitrite NO2 - Permanganate MnO4- Types of compounds The simplest compounds contain only two elements and are called binary compounds. a) Metal-non-metal binary compounds (ionic compounds) The metal is written as the first name and the non-metal ending “ide” forms the last name eg Na2S sodium sulfide MgO magnesium oxide If more than one compound of the metal exists, their oxidation numbers are used eg FeCl2 iron (II) chloride and FeCl3 iron (III) chloride Name the following metal-non-metal compounds (check for a metal then it is as simple as writing the metal name followed by the non-metal ending.
List all the possible places where losses may have occurred. Heating in the laboratory A laboratory also will have an array of heating, cooling and drying equipment such as gas burners, heating mantles, muffle furnaces, hot plates, steam baths, ovens, desiccators and refrigerators. Common gas burners include the bunsen, the meker, batswing and microburner. These burners all depend on a supply of fuel gas and air. The efficiency and heat output of any burner can be controlled by selecting the amount of air and/or gas which passes through the burner . Bunsen burner Batswing burner Meker burner Your teacher will demonstrate the correct ignition procedure for the common laboratory burners . Generally if you are going to leave a bunsen burner alight, but not in use, the yellow “safety” flame should be burning. Non-flame devices are versatile and much safer for use with flammable materials. These include electric hotplates, drying ovens, muffle furnaces, heating mantles and drying cabinets. Practical: 4.4 Heating devices Date Completed: ______________________ Teacher check ________________ Procedure: Analyst signature ____________ Examine the heating equipment on display and complete the following table. Device Description Major Use Safety Hazards Flame dependent devices (Burners)
Systematic errors are those that have a definite value which can be measured and accounted for, that is, they are errors that are possible to avoid, minimise or compensate for. Random errors result from the person, the equipment or the method operating outside its limitations. These errors may or may not be positively identified and so will not always have a definite measurable value. Random errors occur in a random manner. Systematic and random errors can be minimised by: calibration of apparatus and application of correction factors use of blanks, spiked samples, controls, certified reference materials, recovery tests and variations in sample size alternate or independent methods of analysis replicate determinations standard addition techniques internal standard techniques validation using the literature or prior work with similar samples Basic Numerical Methods for Reporting Measurements When any scientific measurement is carried out, it is not enough to simply carry out one analysis, and to report the result. There are too many sources of possible error that can arise, and therefore the analysis should be repeated a number of times to confirm that the measurement obtained is reliable. The result that is reported after several, acceptable, measurements of the same property is the average of the repeats or the mean. This is calculated from the sum of the answers divided by the number of values. For example, an analyst determines the vitamin C content of a sample and she obtains the following results: 24.39 mg/L, 24.18 mg/L, 24.27 mg/L. The reported value for this analysis would be the mean of these determinations, that is: ( 24.39 + 24.18 + 24.27 ) / 3 = 24.28 mg/L. The two attributes needed to accept these data are: accuracy (i.e. the result should be as close as possible to the actual value) precision (i.e. the replicate values should be close to each other). In this case, if the accuracy could not be estimated, the precision would be considered good and the analyst should feel confident with her work. When accuracy estimates are essential (e.g. nutritional labelling, medical analysis), then a number of validation methods exist. Routine validation methods which could be used are:
paper sand evaporating basin basin 1 2 3 Analysis calculations Mass of sand recovered (a) Mass of salt recovered (b) Recovered sand + salt total (a) + (b) Original mass of analytical sample used in test % sand Recovered % salt Recovered 1 2 3 Questions: Discuss any differences between the composition of the original bulk supply and the test results for your recovered samples. Comment on your recovery check. (the agreement between the mass of each of your analytical samples and the recovered sand + salt masses after the analysis. This tells how reliable your results might be.
PART B Perform the following conversions: (1 mark each) 7. 789 nm to m Answer _________________ m 8. 4.25 x 10-4 kL to mL Answer _________________ mL 9. 270 mm2 to m2 Answer _________________ m2 10. 62.3 kg to pounds (1 pound = 454g) Answer _________________ pounds PART C Plot a calibration graph on the supplied graph paper, given the data below: (2 marks)