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The Atom: From Philosophical Idea to Scientific Theory Democritus first suggested the idea that atoms existed but had no experimental support ◦ Atom: the smallest particle of an element that keeps the properties of that element. (Greek: atomos = indivisible) Dalton’s Atomic Theory 1. All elements are composed of tiny indivisible particles called atoms. Dalton’s Atomic Theory 2. Atoms of the same element are identical in size, mass and other properties. Atoms of one element are different from those of another. Dalton’s Atomic Theory 3. Atoms can combine with other atoms in whole number ratios to form compounds H2 O C12H22O11 NOT H2.5O¾ Dalton’s Atomic Theory 4. Chemical reactions occur when atoms are separated, joined or rearranged. Atoms are not changed into atoms of another! Dalton’s Atomic Theory 5. Atoms can not be subdivided, created or destroyed. Atoms are known to be made up of smaller subatomic particles ◦ Electrons ◦ Protons ◦ Neutrons Dalton A simple sphere with no internal structure Thomson Discovered electrons Plum pudding model (negatively charged particles) Rutherford Dense positive nucleus surrounded by electrons Protons – positively charged particles BBC Video Gold Foil Expt Bohr Electrons orbit nucleus in certain energy levels Planetary model Shrodinger Electrons exist in clouds around the nucleus Protons (p+) = + charge; nucleus of the atom Neutrons (n) = no charge; nucleus of the atom Electrons (e-) = - charge; orbit the nucleus Protons and neutrons determine mass Electrons occupy most of the volume of the atom and determine charge WORLD OF CHEMISTRY Crash Course Atoms of different elements have different numbers of subatomic particles Number of protons in the nucleus Elements are arranged by atomic number on periodic table Identifies an element Also tells you how many electrons in a neutral atom Periodic Table ◦ How many p+? ◦ How many e-? Total # of protons and neutrons in an atom Mass numbers are ALWAYS whole numbers ◦ When using the periodic table, round the atomic mass Mass Number??? # of protons = atomic number # of electrons = # of protons # neutrons = Mass # - Atomic # (in a neutral atom) Symbol p+ n0 e- Atomic # Mass # ION = charged atom due to the gain or loss of electron(s) If an atom GAINS an electron = negative ion ◦ anion ◦ Ex: Cl- If an atom LOSES an electron = positive ion ◦ cation ◦ Ex: Ca2+ Symbol Atomic # Mass # # protons # # neutrons electrons Charge Definition – atoms of the same element with different numbers of neutrons ◦ Isotopes differ in mass number ◦ Identified by mass number (ex: C-12 vs C-14) Definition = weighted average mass of the isotopes of the element Reported on the periodic table Based on the mass and abundance of each isotope Atomic mass = Abundance x mass ISOTOPE #1 + Abundance x mass ISOTOPE #2 Repeats for however many isotopes exist for that element…. Atomic mass = Abundance x mass + Abundance x mass Carbon has 3 isotopes: carbon-14 abundance of 0.001% carbon-13 abundance of 1.11% carbon-12 abundance of 98.89 What is the atomic mass of carbon? Atomic mass = Abundance x mass + Abundance x mass Chlorine has 2 isotopes: chlorine-37 abundance of 75.78% chlorine-35 abundance of 24.22% What is the atomic mass of chlorine? Chapter 5 Dmitri Mendeleev (1834-1907) – first person to organize the elements in a chart ◦ Arranged ~ 70 elements by increasing atomic mass ◦ Left blank spaces for elements which were not discovered yet Henry Moseley (1913) – rearranged Mendeleev’s periodic table ◦ Arranged elements by increasing atomic number ◦ Also grouped elements by their properties ◦ Current configuration of the Periodic Table Elements are arranged by atomic number ◦ Columns = groups/families ◦ Rows = periods Periodic Law: periodic repetition of physical and chemical properties Alkali Metals (group 1) ◦ React Violently with water Lithium Sodium Potassium Rubidium Cesium Francium Alkaline Earth Metals (group 2) ◦ Very common in the earth’s surface Beryllium Magnesium Calcium Strontium Barium Radium Transition Metals (Groups 3-12) ◦ Most of the common metals Inner Transition Metals ◦ Placed at bottom of periodic table to condense table ◦ Lanthanide & Actinide Series ◦ All actinides are radioactive (unstable) Halogens (group 17) ◦ Highly reactive Fluorine Chlorine Bromine Iodine Noble Gases (group 18) ◦ All gases ◦ Do not react or combine with any other element Line of Demarcation: jagged “stairs” which separate the left and right side ◦ Metals = left and below the line of demarcation ◦ Nonmetals = right and above the line of demarcation ◦ Metalloids = B, Si, Ge, As, Sb, Te Properties of Metals ◦ Conduct electricity & heat ◦ Malleable ◦ Strong ◦ High melting and freezing points ◦ Mostly solids ◦ Have Luster Properties of Nonmetals ◦ Insulators – do not conduct well ◦ Brittle ◦ Low melting and freezing points ◦ Contain gases and liquids ◦ Are dull Properties of Metalloids have properties of both metals and nonmetals Ex) Silicon ◦ -semi-conductor ◦ -brittle Answer the following in your composition book Questions found on page 129 #33, 36, 38-43, 45-46, 48-49, 53, 57
