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1 Chapter 2 part 1 Slide 2 2 Law of conservation of mass Dalton Mass is neither created or destroyed in chemical rxns. Slide 3 3 Law of definite proportions Dalton In a given compound the relative number and kind of atoms is constant. Example: Water = 2 H and 1 O Slide 4 4 Law of multiple proportions This law is readily explained by Dalton's atomic theory. Suppose a compound is made of element A and element B, giving the formula AB. Since the weight of A is constant and the weight of B is constant, the A:B weight ratio will always be the same. Pg 45 in text (MOVIE)MOVIE) Slide 5 5 Law of multiple proportions when elements combine, they do so in the ratio of small whole numbers Slide 6 6 Daltons Atomic Theory 1. each element is composed of atoms 2. All atoms of a given element are identical 3. A chemical compound is the result of the combination of atoms of 2+ different elements 4. Atoms of an element are not changed into different types of atoms by chemical rxns (MOVIE) Slide 7 7 Millikan Discovered the charge and mass of an electron 1.6 X 10 -19 C (coulomb) Slide 8 8 Radioactivity Three types of radiation Alpha +2 charge Gamma no charge Beta -1 charge Slide 9 9 Rutherford Most of the mass of an atom and all of its positive charge resides in a very small dense region (nucleus) Most of the volume of the atom is empty space around the nucleus Slide 10 10 Slide 11 11 Atomic Structure Proton Symbol p + Charge = 1.602 x 10 -19 C (coulomb) Mass = 1.0073 amu Electron Symbol = e - Charge = -1.602 x 10 -19 C Mass = 5.486 x 10 -4 amu Neutron Symbol = n 0 no charge Mass = 1.0087 amu Slide 12 12 Units = amu or g/mol Slide 13 13 A Z X A = Atomic mass ( p+ n) Z = Atomic number ( p) X = element Symbol Complete Chemical Symbol Slide 14 14 Question How many neutrons, protons and electrons are in carbon? C 12 6 C = Carbon 12 = Atomic Mass ( protons + neutrons) 6 = atomic Number (protons) Slide 15 15 Answer 12 = p + n 6 = protons 12 6 = 6 neutrons In an atom with out a charge the number of protons is equal to the number of neutrons Thus: 6 electrons Slide 16 16 Question Write the complete chemical symbol for the following elements. Magnesium Sodium Tungsten Slide 17 17 Determining Sub Atomic Particles 12 6 C = Carbon 12 = Atomic Mass/weight ( protons + neutrons) 6 = atomic Number (protons) C Slide 18 18 Isotopes Atoms of a given element that differ in number of neutrons and thus in mass. IsotopeProtonsElectronsNeutrons 11 C665 12 C666 Slide 19 19 Isotopes Cont. When writing isotopes the atomic number ( # of p + ) stays the same, but the Atomic Mass (p + + n 0 ) changes due to the addition and subtraction of neutrons. Slide 20 20 Formulas Chemical Indicates actual numbers and type of atoms in a molecule H 2 O 2 C 2 H 4 Empirical gives only relative number of atoms of each type HO CH 2 Structural individual bonds are shown, indicated by lines Slide 21 21 average atomic mass Amu = Average Atomic Mass Unit The average atomic mass (weight) of an element is equal to the sum of the products of each isotopes mass (in amu) multiplied by its relative abundance. Slide 22 22 EXAMPLE OF AVERAGE ATOMIC MASS PROBLEM Naturally occurring chlorine is 75.53% Cl- 35 which has an atomic mass of 34.969 amu, and 24.47% Cl-37, which has an atomic mass of 36.966 amu. Calculate the average atomic mass of chlorine. Slide 23 23 EXAMPLE OF AVERAGE ATOMIC MASS PROBLEM (CONT) Average atomic Mass = [ (%/100) (Atomic Mass) ] Average atomic mass = (0.7553) (34.969 amu) + (0.2447) (36.966 amu) = 26.41 amu + 9.045 amu = 35.46 amu NOTE: The average atomic mass of an element is closest in value to the atomic mass of the most abundant isotope. Slide 24 24 Alkali metals Alkaline Earth Metal Halogens Metals Non Metals Metalloids TRANSITION METALS Slide 25 25 DIATOMIC SEVEN Slide 26 26 Nomenclature Chapter 2 part 2 Check out these videos for more help or if you are absent Naming molecular compounds Writing formulas for molecular compounds Naming ionic compounds video Writing formulas for Ionic compounds Slide 27 27 2.7 Ions and ionic compounds When negative electrons are removed or added to an atom the charge of that atom changes from its neutral state to a charged state ( + or - ) Ion: charged particle Slide 28 28 a cation is a particle that carries a positive electrical charge. The cation gets this positive charge from losing negatively charged electrons. Slide 29 29 Anions are ions that carry a negative electrical charge. Anions get their negative charge by gaining one or more electrons Slide 30 30 Trick Na + Cl - Slide 31 31 Example Na = atomic number 11 atomic mass = 23 11 protons, 12 neutrons, 11 electrons Na - = 11 protons, 12 neutrons, 12 electrons We added an additional negative charge (e - ) creating a negatively charged particle. 11 + -12 = -1 charge on Na Slide 32 32 Reverse example Na = atomic number 11 atomic mass = 23 11 protons, 12 neutrons, 11 electrons Na + = 11 protons, 12 neutrons, 10 electrons We subtracted a negative charge (e - ) creating a positively charged particle. 11 + -10 = +1 charge on Na Slide 33 33 Question How many protons and electrons does Se 2- ion posses? How many protons and electrons does Cr 3+ ion posses? What kind of ions are these molecules and why? Slide 34 34 Answer Se 2- : anion 34 protons (atomic number) 36 electrons = -34 + -2 = -36 Cr 3+ : Cation 24 protons (atomic number) 21 electrons = 24 3 = 21 Slide 35 35 Nomenclature (Naming) As of 2007 there are 31,000,000 known compounds. Your are options are A: memorize all 31,000,000 names B: Learn how to name them memorize about 50 things that will allow you to name all 31,000,000. Slide 36 36 Polyatomic Ions Atoms joined as a molecule, but they have a net positive or negative charge. Example: NO 3 -, SO 4 2- I will give you a list. You need to try to memorize them all yes all. Slide 37 37 Polyatomic Ion Rap Slide 38 38 Cation and Anions to Memorize Write these on your binder periodic table +/-3 +/-4 Slide 39 39 Putting the pieces together Na + Cl - Mg 2+ 2Cl - NaCl is an ionic compound MgCl 2 is an ionic compound Slide 40 40 Ionic Compounds Contain both positively and negatively charged ions. In general ionic compounds are made of metals and nonmetals. Slide 41 41 Covalent compounds 2 negatively charged elements 2 non metals Slide 42 42 Slide 43 43 Slide 44 44 Question Write the ionic compound for: Magnesium and Nitrogen Magnesium and NO 3 - Slide 45 45 Answer Mg 3 N 2 Mg(NO 3 ) 2 Count the total number of each type of atom in the molecules above. Slide 46 46 Homework Pg 71 #s 37,40,45,47,48 Slide 47 47 2.8 Naming ionic compounds PINK SHEET Slide 48 48 Slide 49 49