GC1Week2Lesson1 (1).pptx

Atoms, Molecules, and Ions ROMINA D. MEDIANA Gen. Chem 1 Subject Teacher  SESSION OBJECTIVES At the end of the session, the learners should be able to: explain the basic laws of matter (Law of Conservation of Mass, Law of Definite Proportion, and Law of Multiple P...

Atoms, Molecules, and Ions ROMINA D. MEDIANA Gen. Chem 1 Subject Teacher  SESSION OBJECTIVES At the end of the session, the learners should be able to: explain the basic laws of matter (Law of Conservation of Mass, Law of Definite Proportion, and Law of Multiple Proportion) led to the formulation of Dalton’s Atomic Theory describe Dalton’s Atomic Theory differentiate among atomic number, mass number, and isotopes, and which of these distinguishes one element from another; write isotopic symbols; differentiate among atoms, molecules, ions and give examples; name compounds given their formula and write formula given the name of the compound  LECTURE PROPER Historical Background of Atomic Structure Modern View of Atomic Structure Molecules and Ions Nomenclature of Compounds The Building Blocks of Matter: Atoms - - - ++ + - + + + - + + - - - WHAT IS AN ATOM? In 400 B.C the Greeks tried to understand matter (chemicals) and broke them down into earth, wind, fire, and air. Democritus believe that all matter is made of very small particles. He called these particles atoms(Greek atomos, meaning “tiny, indivisible” particles Atoms are the basic units of matter LAWS OF CHEMICAL CHANGES 1. Law of Conservation of Mass ( Antoine Lavoisier, 1743-1794) -In a chemical reaction, no change in mass takes place. The total mass of the products is equal to the total mass of the reactant. Mass is neither created nor destroyed Ex. Prob. 1. A 300 kg tree that is burning down, when it is done burning down, there are only ashes left and all of them together weigh 10 kg. Well, it makes you wonder where the other 290 kg went. Prob. 2. If heating 10.0 grams of calcium carbonate (CaCO3) produces 4.4 g of carbon dioxide (CO2) and 5.6 g of calcium oxide (CaO), show that these observations are in agreement with the law of conservation of mass. Solution Mass of the reactants=Mass of the products 10.0g of CaCO3 =4.4g of CO2+5.6g of CaO 10.0g of reactant=10.0g of products Because the mass of the reactant is equal to the mass of the products, the observations are in agreement with the law of conservation of mass. Prob. 3 Potassium hydroxide ( KOH ) readily reacts with carbon dioxide ( CO2 ) to produce Potassium carbonate ( K2CO3 ) and water ( H2O ). How many grams of potassium carbonate is produced if 224.4 g of KOH reacted with 88.0 g of CO2. The reaction also produced 36.0 g of water. 2. Law of Definite Proportion ( Joseph Proust, 1754-1826) - A compound always contains the same constituent elements in a fixed or definite proportion by mass. Ex. 1. As an example, any sample of pure water contains 11.19% hydrogen and 88.81% oxygen by mass. It does not matter where the sample of water came from or how it was prepared. Its composition, like that of every other compound, is fixed. Ex. 2 CO2 – C= 27.29% CO – C=42.86% O = 72.71% O = 57.14% H2O – H = 5.97% H2O2 – H=11.2% O = 94.06% O = 88.8% 3. Law of Multiple Proportions - If two elements can combine to form more than one compound, the masses of one element that will combine with a fixed mass of the other element are in a ratio of small whole numbers. JOHN DALTON’S ATOMIC THEORY 1. Elements are made up of very small particles known as atoms. Atoms can never be created nor destroyed. 2. All the atoms of an element are identical in mass and size, and are different from the atoms of another element. Dalton used the different shapes or figures to represent different elements, as follows: 3. Compounds are composed of atoms of more than one element, combined in definite ratios with whole number values. 4. During a chemical reaction, atoms combine, separate, or rearrange. No atoms are created Dalton's theory has not proven to be correct under all circumstances: Postulate 1 - was proven incorrect when scientists divided atoms in a process called nuclear fission. Postulate 2 - was proven incorrect by the discovery that not all atoms of the same element have the same mass; there are different isotopes. Postulate 3 – provides explanation to the Law of Definite Proportions: if all the atoms of an element are alike in mass and if atoms unite in fixed numerical ratios, the percent composition of a compound must have a unique value without regards to the sample analyzed. - this postulate was also considered as a loophole and was corrected by Dalton by proposing The Law of Multiple Proportions: states that if two elements form more than one compound between them, the masses of one element combined with a fixed mass of the second element form in ratios of small integers. The illustration of the third rule of the atomic theory correctly depicts this law. Postulate 4 – provides explanation to the Law Of Conservation of Mass: if atoms of an element are indestructible, then the same atom must be present after a chemical reaction as before and, and the mass must constant. HISTORICAL DEVELOPMENT OF MODELS OF THE COMPONENTS AND STRUCTURE OF THE ATOM Ernest Rutherford’s (1871-1937) Where exactly are those electrons? Thomson’s Theory: “Plum Pudding”  electrons embedded in a positive pudding. Rutherford’s idea:  Shoot something at them to see where they are. Rutherford’s has an idea… What if I shoot alpha radiation at gold atoms in gold foil? Discovery of the nucleus  Flourescent Screen Lead Uranium bloc k Gold Foil He Expected  The alpha particles to pass through without changing direction very much.  Because…  The positive charges were spread out evenly. Alone they were not enough to stop the alpha particles. What he expected Because Because, he thought the mass was evenly distributed in the atom Because, he thought the mass was evenly distributed in the atom What he got How he explained it  Atom is mostly empty.  Small dense, positive piece at center.  Alpha particles are deflected by it if they get close enough. + + Rutherford’s Conclusion (1911)… Small, dense, positive nucleus. Equal amounts of (-) electrons at large distances outside the nucleus. MODERN VIEW OF ATOMIC STRUCTURE  ATOMIC AND MASS NUMBERS ATOMIC NUMBER: equal to the number of protons in the nucleus. All atoms of the same element have the same number of protons. Denoted by “Z”. MASS NUMBER: equal to the sum of the number of protons and neutrons for an atom. Fill up the following table: element Atomic Mass Number of number number protons electrons neutrons 30 35 6 6 47 109 29 36 48 22 76 114 86 136  ATOMIC MASS The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom. A carbon (C) atom with 6 protons and 6 neutrons is assigned a mass of exactly 12.000. Atomic mass unit (amu) is one-twelfth of the mass of an atom of carbon with 6 protons and 6 neutrons. 1 amu = 1.661 × 10-24 g  ISOTOPES Atoms of the same element with different masses. Isotopes have different numbers of NEUTRONS, thus different mass numbers. ISOTOPES Discovered by American Physicist A. J. Dempster and English Chemist f. W. Anston (1914) Isotopes are classified as: a. stable – do not exhibit radioactivity, which explains why they exist and persis in nature. -occurs in nature and are abundant on earth like O-16 and C12 b. unstable – exhibit radioactivity (tremendous emission of invisible rays due to the splitting of the nucleus of an atom) - called radioisotopes Uses: a. dating fossils and rocks - radioactive decay rates tell the age of rocks and fossils - U -238, half life 4.5 x 109 yrs b. Radiocarbon dating – determine the age of once a living organism, using carbon-14, half life is 5730 years c. medical uses – radioisotopes are used to detect and treat abnormalities in the body  ISOTOPES Table 1. Some Isotopes of Carbon* Isotopic Number of Number of Number of Symbol Proton Electron Neutron 11 C 6 6 5 12 C 6 6 6 13 C 6 6 7 14 C 6 6 8 * Almost 99% of the carbon found in nature is 12 C. HOW TO FIND THE ATOMIC MASS OF AN ELEMENT Atomic Mass –is not a whole number. It is the weighted average of the masses of isotopes of a particular element. The percentage of isotopes of a particular element. The percentage abundance of each isotope is taken into account. Example: The percent abundance of the different isotopes of silicon are 14Si28 = 92.21%, 14Si29 = 4.70%, and 14Si30 = 3.09%. Compute the weighted average of the masses of the Silicon isotopes.  MOLECULES AND IONS Molecules composed of two or more atoms are chemically bound together, molecules are formed. Several elements are found in nature in molecular form. One example is oxygen gas whose chemical formula is O2 (read as “Oh two”).  MOLECULES AND IONS Molecular Formula (MF) – a chemical formula that indicates the actual number of atoms in a molecule. For example, the molecular formula of hydrogen peroxide is H2O2 Empirical Formula (EF) – a chemical formula that only gives the relative number of each type of atom in a molecule. The subscripts in an empirical formula are always in the lowest possible ratio. For example, the empirical formula of hydrogen peroxide is HO. Other examples: Ethane (MF: C2H6; EF: CH3)  MOLECULES AND IONS Structural Formula – shows the composition as well as the connectivity of the atoms as well. – atoms are represented by their chemical symbol and lines are used to represent the chemical bonds that hold the atoms together. For example, Water (H2O) Hydrogen Peroxide (H2O2)  water Hydrogen peroxide Molecular Formula H2O H 2 O2 Empirical Formula H2O HO Structural Formula H-O-H H-O-O-H  MOLECULES AND IONS IONS - charged particles formed after electrons are either removed or added to an atom Cation – pronounced as CAT-ion – a positively charged ion. Anion – pronounced as AN-ion – a negatively charged ion. In general, METALS FORM CATIONS while NONMETALS FORM ANIONS.  MOLECULES AND IONS Polyatomic ions ions composed of more than one atom Simple Ions ions composed of only one atom ASSESSMENT A. Determine whether the following are molecules or ions 1. Fluorine gas (F 2) 2. Lithium fluoride (LiF) 3. Glucose ( C6H12O6) 4. Cr3+ 5. PO43- B. Indicate the number of electrons lost or gained in forming these ions: 6. NH4+ 7. CO32- 8. Gold(III) 9. OH- 10. SO43- IONIC COMPOUNDS - Are neutral compounds - Made up of ions - Neutral, “The sum of positive charges and negative charges must be equal to zero.” Example: 1. NaBr = +1 + (-1) = 0 2. MgCl2 = +2 + 2(-1) =0 3. Fe2O3 = 2(+3) + 3(-2) = 0 4. P2O7 4-  Models of the Atom Dalton’s model Greek model Thomson’s plum-pudding Rutherford’s model Bohr’s model Charge-cloud model (1803) (400 B.C.) model (1897) (1909) (1913) (present) 1803 John Dalton 1897 J.J. Thomson, a British 1911 New Zealander 1926 Erwin Schrödinger scientist, discovers the electron, Ernest Rutherford states 1913 In Niels Bohr's develops mathematical pictures atoms as leading to his "plum-pudding" that an atom has a dense, model, the electrons move equations to describe the tiny, indestructible model. He pictures electrons positively charged nucleus. in spherical orbits at fixed motion of electrons in distances from the nucleus. particles, with no embedded in a sphere of Electrons move randomly in atoms. His work leads to positive electric charge. the space around the nucleus. the electron cloud model. internal structure. 1800 1805..................... 1895 1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1924 Frenchman Louis 1932 James 1904 Hantaro Nagaoka, a de Broglie proposes that Chadwick , a British Japanese physicist, suggests moving particles like electrons physicist, confirms the that an atom has a central have some properties of waves. existence of neutrons, nucleus. Electrons move in Within a few years evidence is which have no charge. orbits like the rings around Saturn. collected to support his idea. Atomic nuclei contain neutrons and positively charged protons. orin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 125  Match The Models Billiard Plum Energy Nucleus Neutrons Ball Pudding Levels