Chapter 2: Medicine RG PDF - Atoms, Molecules, and Ions

Atoms, Molecules and Ions Chapter 2.  2.1: The Atomic Theory of Matter Dalton’s Atomic Theory (1808) 1. Elements are composed of extremely small particles called atoms. All atoms of a given element are identical, having the same size, mass and chemical properties. The a...

Atoms, Molecules and Ions Chapter 2.  2.1: The Atomic Theory of Matter Dalton’s Atomic Theory (1808) 1. Elements are composed of extremely small particles called atoms. All atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the atoms of all other elements. 2. Compounds are composed of atoms of more than one element. The relative number of atoms of each element in a given compound is always the same. 3. Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions. 2.1  2 Law of multiple proportions 2.1 16 X + 8Y 8 X2Y Law of conservation of Mass 2.1 J. Thomson's experiment and the charge-to-mass ratio of the electron The first is the experiment of Joseph John Thomson, who first demonstrated that atoms are actually composed of aggregates of charged particles. Prior to his work, it was believed that atoms were the fundamental building blocks of matter. The first evidence contrary to this notion came when people began studying the properties of atoms in large electric fields. If a gas sample is introduced into the region between two charged plates, a current flow can be observed, suggesting that the atoms have been broken down into charged constituents. The source of these charged particles is a heated cathode that, in fact, causes the atoms of the sample to ionize. These were known as cathode rays. In 1897, Thomson set out to prove that the cathode rays produced from the cathode were actually a stream of negatively charged particles called electrons. In 1897, Thomson showed that cathode rays were composed of previously unknown negatively charged particles (now called electrons), which he calculated must have bodies much smaller than atoms and a very large charge-to-mass ratio 2.2: The discovery of Atomic Structure J.J. Thomson, measured mass/charge of e- (1906 Nobel Prize in Physics) 2.2  Measured mass of e- (1923 Nobel Prize in Physics) e- charge = -1.60 x 10-19 C Thomson’s charge/mass of e- = -1.76 x 108 C/g e- mass = 9.10 x 10-28 g 2.2 Radioactivity (Uranium compound) 2.2 The Nuclear Model of the Atom 2.2  (Proto discovery) α particle velocity ~ 1.4 x 107 m/s (~5% speed of light) 1. atoms positive charge is concentrated in the nucleus 2. proton (p) has opposite (+) charge of electron (-) 3. mass of p is 1840 x mass of e- (1.67 x 10-24 g) 2.2  Rutherford’s Model of the Atom atomic radius ~ 100 pm = 1 x 10-10 m nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m 2.2 Chadwick’s Experiment (1932) The discovery of Neutron H atoms - 1 p; He atoms - 2 p mass He/mass H should = 2 measured mass He/mass H = 4 α + 9Be 1 n + 12C + energy neutron (n) is neutral (charge = 0) n mass ~ p mass = 1.67 x 10-24 g 2.2 2.3: The modern view of Atomic Structure Subatomic Particles (Table 2.1) mass p = mass n = 1840 x mass e- 2.2 Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei Mass Number A ZX Element Symbol Atomic Number 1 2 3 1H 1H (D) 1H (T) 235 238 92 U 92 U 2.3 2.3  Do You Understand Isotopes? How many protons, neutrons, and electrons are in 146 C? 6 protons, 8 (14 - 6) neutrons, 6 electrons How many protons, neutrons, and electrons are in 126 C? 6 protons, 6 (12 - 6) neutrons, 6 electrons 2.3  Noble Gas 2.4 Halogen 2.5: The Modern Periodic Table Group Period Alkali Earth Metal Alkali Metal  2.6: Molecules and Molecular Compounds A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds H2 H 2O NH3 CH4 A diatomic molecule contains only two atoms H2, N2, O2, Br2, HCl, CO A polyatomic molecule contains more than two atoms O3, H2O, NH3, CH4 2.5 2.7: Ions and Ionic Compounds An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. 11 protons + 11 protons Na 11 electrons Na 10 electrons anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. 17 protons 17 protons - Cl 17 electrons Cl 18 electrons 2.5 A monatomic ion contains only one atom Na+, Cl-, Ca2+, O2-, Al3+, N3- A polyatomic ion contains more than one atom OH-, CN-, NH4+, NO3- 2.5  Do You Understand Ions? + 27 3 How many protons and electrons are in 13 Al ? 13 protons, 10 (13 – 3) electrons How many protons and electrons are in 78 34 Se 2- ? 34 protons, 36 (34 + 2) electrons 2.5 2.5 2.6 A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance An empirical formula shows the simplest whole-number ratio of the atoms in a substance molecular empirical H2O H2O C6H12O6 CH2O O3 O N2H4 NH2 2.6 ionic compounds consist of a combination of cations and an anions the formula is always the same as the empirical formula the sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero The ionic compound NaCl 2.6 Formula of Ionic Compounds 2 x +3 = +6 3 x -2 = -6 Al2O3 Al3+ O2- 1 x +2 = +2 2 x -1 = -2 CaBr2 Ca2+ Br- 1 x +2 = +2 1 x -2 = -2 Na2CO3 Na+ CO32- 2.6 Some Polyatomic Ions (Table 2.3) 2.7  2.8: Naming inorganic compounds Ionic Compounds – often a metal + nonmetal – anion (nonmetal), add “ide” to element stem name BaCl2 barium chloride K2O potassium oxide Mg(OH)2 magnesium hydroxide KNO3 potassium nitrate 2.7  Transition metal ionic compounds – indicate charge on metal with Roman numerals FeCl2 2 Cl- -2 so Fe is +2 iron(II) chloride FeCl3 3 Cl- -3 so Fe is +3 iron(III) chloride Cr2S3 3 S-2 -6 so Cr is +3 (6/2) chromium(III) sulfide 2.7  Naming Molecular compounds – nonmetals or nonmetals + metalloids – common names H2O, NH3, CH4, C60 – element further left in periodic table is 1st – element closest to bottom of group is 1st – if more than one compound can be formed from the same elements, use prefixes to indicate number of each kind of atom – last element ends in ide 2.7  Molecular Compounds HI hydrogen iodide NF3 nitrogen trifluoride SO2 sulfur dioxide N2Cl4 dinitrogen tetrachloride NO2 nitrogen dioxide TOXIC! N2O dinitrogen monoxide Laughing Gas 2.7  Names and Formulas of Acids An acid can be defined as a substance that yields hydrogen ions (H+) when dissolved in water. HCl Pure substance, hydrogen chloride Dissolved in water (H+ Cl-), hydrochloric acid An oxoacid is an acid that contains hydrogen, oxygen, and another element. HNO3 nitric acid H2CO3 carbonic acid H2SO4 sulfuric acid 2.7 2.7  Names and Formulas of Base A base can be defined as a substance that yields hydroxide ions (OH-) when dissolved in water. NaOH sodium hydroxide KOH potassium hydroxide Ba(OH)2 barium hydroxide 2.7