Introduction to Organic and Biochemistry (CHE 124) Reading Assignment General, Organic, and Biological Chemistry: An Integrated Approach 3 rd. Ed. Ramond Chapter 2 Atoms and Elements Work Problems Chapter 2: 3, 5, 12, 15, 18, 20, 24, 26, 34, 36, 38, 40, 44, 46, 48, 50, 52, 54, 56,, 58, 60, 62, 64, 71, 72, 73, 74, 76, 88, 90.

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) ChargeLocation Proton x Nucleus Neutron x (neutral) Nucleus Electron x x Outside of Nucleus Amu = atomic mass unit also called Dalton.

Elements Ancient Greeks recognized four elements –Earth, air, fire and water. Modern definition –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 occuring) Elements are organized on the Periodic Chart. (See next slide). Learn the elements / symbols on the handout.

Elements Have Two Important Numbers 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 ( ), 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

GroupGroup Period -horizontal row, numbered –Numbered top to bottom. –Organized by atomic number Group or Family - vertical column, –Numbered 1 – 8 A and B’s –New system 1 – 18 (L to R). –Elements in a group have similar chemical properties. Period

–Main group elements groups A’s 1, 2, 13 – 18 –Transition Metals B’s groups 3 – 12 –Lanthanides elements –Actinides elements Note location of Metals Nonmetals Metalloids Note Po: error in book Note B: error on this table

Metals vs Nonmetals Lustrous –Shiny Malleable –Able to pound on without breaking Ductile –Able to stretch into a wire MetalsNonmetalsMetalloids Conduct electricity and heat NonconductorIntermediate LustrousNonlustrousIntermediate MalleableBrittleIntermediate DuctileBrittleIntermediate

–Groups with common names –Group 1A (1) = Alkali Metals –Group 2A (2) = Alkaline Earth Metals –Group 7A (17) = Halogens –Group 8A (18)= Noble Gases

Electronegativity –Measure of how tightly an element holds onto its electrons. Trends on Periodic Chart

Conversion Factors

Mole (Avagadro’s number) Atoms are very small –How do we keep track of the number of atoms? Mole (n) = X 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 = 2n 2 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

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 C C C # neutrons # protons = atomic weight - atomic number = atomic number Atomic Mass Atomic Number Eight isotopes of carbon are (A = 9 – 16)

An Element May Differ in Number of Neutrons (Cont’) C C C # neutrons # protons Atomic Mass Atomic Number

Isotopes of hydrogen 1 H = hydrogen 2 H = deuterium 3 H = 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 – days –Plutonium ,000 yrs. –Uranium million yrs.

Types of Radiation NameSymMake upChargeStopped by Alpha particles α 2 protons + 2 neutrons (He nucleus) 2+ paper Beta particles βElectron1-plastic Positronsβ +Positively charged electron 1+plastic Gamma rays γElectronmagnetic raditation 0Concrete / lead See Table 2.7 for type of radiation emitted by particular isotopes.