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Introduction to Organic and Biochemistry (CHE 124) Reading Assignment General, Organic, and Biological Chemistry: An Integrated Approach 4th. Ed. Raymond Chapter 2 Atoms and Elements Answers to odd numbered problems in textbook are found in the book’s index. Atom • The building block of matter. – Greek (Atomos meaning indivisible). • Atoms are composed to three subatomic particles – Draw a diagram of carbon. Subatomic Particle Mass (g) Mass (amu) Charge Location Proton 1.6726 x 10- 24 1.0073 + Nucleus Neutron 1.6750 x 10-24 1.0087 0 Nucleus (neutral) Electron 9.110 x 10-28 5.486 x 10-4 Amu = atomic mass unit also called Dalton. - Outside of Nucleus Elements • Ancient Greeks recognized four elements – Earth, air, fire and water. • Modern definition – Element - substance that contains only on type of atom. • Elements cannot be broken down into substances with different properties by chemical means. – 112 known elements (91 naturally occurring) • Elements are organized on the Periodic Chart. (See next slide). • Learn the elements / symbols on the handout. Elements Have Two Important Numbers A Z X • Atomic Mass, A • Atomic Number, Z • Symbol of Element, X Element Defined by Number of Protons • Atomic Mass, A 12 = # protons + # neutrons C • Atomic Number, Z 6 = # protons protons = electrons The number of protons (atomic number) defines an element. Periodic Chart • See the inside front cover of your textbook. – Dmitri Mendeleev (1836-1907), along with others, arranged elements by chemical properties onto primitive Periodic Table (1869) • Left space for elements unknown at the time • Predicted detailed properties for elements as yet unknown G r • Period -horizontal row, numbered 1 - 7 – Numbered top to bottom, organized by atomic number o u • Group or Family - vertical column, – Numbered 1 – 8 A and B’s p – “New” system 1 – 18 (L to R). – Elements in a group have similar chemical properties. 8A 1A 3A 2A Period 3B 4B 5B 6B 7B 8B 1B 2B 4A 5A 6A 7A – Main group elements Note location of • groups A’s 1, 2, 13 – 18 Metals – Transition Metals Nonmetals • B’s groups 3 – 2 Metalloids – Lanthanides • elements 58 - 71 – Actinides • elements 90 - 103 Metals vs Nonmetals Metals Nonmetals Metalloids Conduct electricity and heat Lustrous Malleable Ductile Nonconductor Intermediate Nonlustrous Brittle Brittle Intermediate Intermediate Intermediate • Lustrous – Shiny • Malleable – Able to pound on without breaking • Ductile – Able to stretch into a wire – Groups with common names 1A 2A – – – – 3B Group 1 (1A) = Alkali Metals Group 2 (2A) = Alkaline Earth Metals 3A 4A Group 17 (7A) = Halogens Group 18 (8A)= Noble Gases 4B 5B 6B 7B 8B 1B 2B 8A 5A 6A 7A Trends • Electronegativity – Measure of how tightly an element holds onto its electrons. Conversion Factors Mole (Avagadro’s number) • Atoms are very small – How do we keep track of the number of atoms? • Mole (n) = 6.022 X 1023 atoms / 1 mole – the mass in grams of one mole of a substance is numerically equal to its formula mass (molecular mass). • By knowing Avogadro’s number and the atomic mass, it is now possible to calculate the mass of a single atom in grams. In the laboratory, substances are weighed on balances, in units of grams • Significance of the Mole – The mole allows us to relate the number of grams of a substance to the number of atoms or molecules of a substance Problems • How many Carbon atoms are in 30 g of Carbon? • What is the weight in grams of 0.45 moles of gold (Au)? Bohr Model of the Atom • Protons and neutrons are located in the nucleus. • Electrons orbit the nucleus in specific orbits with each orbit corresponding to a different energy level. – Ground state (most stable state) when electrons are in energy levels as near as possible to the nucleus – Excited state when electrons is pushed into an orbit farther from the nucleus. • When electrons move from an excited state (higher energy level) to the ground state (lower energy level), the energy produced is given off often as light. • Worked well to explain the emision spectrum of hydrogen, but not other elements. – Figure 2.12 p. 47. Line spectrum. Quantum Mechanic Model of the Atom • In 1926, Erwin Schrodinger wrote a series of mathematical equations that described electron energy levels in a new way. • Quantum Mechanics – Energy levels called atomic orbitals • Orbitals are three-dimensional regions of space where there is a high probability of finding an electron (electron cloud). • See Figure 2.13 p. 48. • Maximum number of electrons per energy level = 2n2 • N=energy level. – Table 2.5 p. 49 Give the Ground State Electron Distribution for the first 20 elements. (use periodic chart and board to demonstrate) Energy Level (n) Maximum Number of Electrons 1 2 2 8 3 18 4 32 Valence Electrons • Valence electrons – Electrons in the highest numbered, occupied energy level. – These are the “reactive” electrons. – NOTE: elements in the same group, have the same number of electrons in the valance shell. Electron Dot Structures (Lewis dot structures) • Representation of the number of electrons in an elements valence shell. – Draw only the valence electrons. – See figure 2.15 p. 51 An Element May Differ in Number of Neutrons • Isotope - element with the same number of protons, but different number of neutrons. Atomic Mass Atomic Number # protons 12 C 6 13 14 C 6 = atomic number C 6 Eight isotopes of carbon are (A = 9 – 16) # neutrons = atomic weight - atomic number An Element May Differ in Number of Neutrons (Cont’) Atomic Mass Atomic Number 12 C 6 13 14 C 6 C 6 # protons 6 6 6 # neutrons 6 7 8 Isotopes of hydrogen • 1H = hydrogen • 2H = deuterium • 3H = tritium • Each isotope of hydrogen has a name. • Z = 1 for each isotope of H. • SEE TABLE 2.8 Page 59 for list of radioisotopes used in medicine! Half Life • Time required for one half of atoms of radioisotope to decay. • Examples – Radon – 222 – Plutonium 239 – Uranium 238 3.8 days 24,000 yrs. 4.5 million yrs. Types of Radiation Name Alpha particles Beta particles Positrons Gamma rays Sym α β β+ γ Make up 2 protons + 2 neutrons (He nucleus) Electron Positively charged electron Electronmagnetic raditation Charge Stopped by paper 2+ 1- plastic 1+ plastic 0 Concrete / lead See Table 2.7 for type of radiation emitted by particular isotopes.