Understanding the Macroscopic World • The connection between the microscopic atom and the macroscopic element is the key to understanding the chemical world.
Atoms • An atom is the smallest identifiable unit of an element. • Similarities and differences on the atomic scale correlate with similarities and differences on the macroscopic scale.
Protons Determine the Element • The atomic number, Z, represents the number of protons in the nucleus of an atom. • The charge of a proton is assigned numerical value of +1. • Protons constitute a significant part of the mass of an atom. • Mass of a proton is 1.0 amu
Chemical Symbols • Symbols are an abbreviation of the chemical name which can be based on: • The English name for the element: hydrogen H • The Greek or Latin name: ferrum (iron) Fe • Their place of discovery: europium Eu • The scientist honored by the naming: curium Cm
Electrons • A neutral atom has as many electrons outside its nucleus as protons within its nucleus. • The opposing charges of protons and electrons hold electrons within a spherical region surrounding the nucleus. • Atoms can lose and gain one or more electrons.
Neutrons • Neutrons are almost as massive as protons but carry no electrical charge. • The number of neutrons in the atoms of an element can vary resulting in ISOTOPES. • Can be naturally occurring or man-made • The sum of neutrons and protons in an atom is called the mass number of the atom.
Atomic Mass • Atomic masses listed on the periodic table are weighted averages of the masses of each naturally occurring isotope for that element. • Silver has two naturally occurring isotopes. One has a mass of about 107 amu and the other has a mass of about 109 amu. • Silver -107 has an abundance in nature of 51.84%. • Silver -109 has an abundance in nature of 48.16%.
Atomic Mass Calculate the average atomic mass of silver. Silver has two naturally occurring isotopes. • One has a mass of 106.90509 amu (abundance in nature of 51.84%.) • The other has a mass of 108.90476 amu (abundance in nature of 48.16%.) 106.90509 amu ( 0.5184) = 55.42 amu 108.90476 amu (0.4816) = 52.45 amu 107.87 amu
Molar Mass Calculate the Molar Mass of Calcium carbonate The mass of one mole of a compound. • Calcium carbonate • Chemical Formula CaCO3 Calcium 40.08 grams X 1 mole = 40.08 grams Carbon 12.01 grams X 1 mole = 12.01 grams Oxygen 16.00 grams X 3 moles = 48.00 grams 100.09 grams
Periodic Law • Mendeleev listed the known elements in order of increasing atomic mass, grouping those with similar properties. • He noticed that certain similar properties would recur in a periodic fashion. • His tabulation is the precursor to our modern periodic table.
Mendeleev and the Periodic Table • Proposed that elements would be discovered to fill in gaps in the table. • Proposed that some measured atomic masses were in error. • Summarized a large number of observations • The underlying reasons for periodic behavior were as yet unknown • The Bohr model and the quantum mechanical model were needed to explain the observations.
The Bohr Model • This is a MODEL of the atom that links electron behavior (microscopic) to the periodic law (macroscopic).
Bohr Diagrams/Electron Configurations • Based on the behavior of electrons as particles • Electron orbits • Specified with n, the orbit’s quantum number • Fixed energies • Fixed radii • Maximum number of electrons based on n • This model is an oversimplification (as are most models). • Atoms with full outer orbits are extremely stable. • Atoms with outer orbits that are not full are unstable and will undergo chemical reactions attempting to fill the outer orbit.
The Quantum Mechanical Model • Based on the behavior of electrons as waves • Replace Bohr’s orbits with orbitals, a representation of electron location as the probability of finding it in a certain region of space. • Orbitals are grouped into shells and fill similarly to Bohr’s orbits.
Determinism and Quantum Mechanics • Specifics of orbital filling are beyond the scope of this text…BUT • The statistical nature of the quantum mechanical model rocked the scientific establishment. • An indeterminate universe • Both models are useful even though Bohr’s, by experiment, has been shown to be invalid.
Families of Elements • Also called groups • Based on outer electron configurations • Vertical columns • Alkali metals • Alkaline earth metals • Chalcogens • Halogens • Noble gases
Molecular Elements • Some elements occur as diatomic molecules.
The Mole Concept • Counting particles as small as atoms is impractical. • The mole concept allows us to relate the mass of a sample of an element to the number of atoms within it. • The unit of comparison is called a mole and corresponds to 6.022 x 1023.
Avogadro’s Number • Determined such that the numerical value of the atomic mass of an element in amu is equal to the molar mass of that element in grams per mole. • These relationships of grams, moles, and atoms can be used as conversion factors.
Chapter Summary Molecular Concept • Atomic Number and Mass Number • Isotopes • Molar Mass • Bohr Model • Quantum Mechanical Model • Orbitals • Societal Impact • Chemical processes that cause change are caused by changes in atoms or molecules. • Pollution results from “misplaced” atoms. Atoms that are not where they are supposed to be located. • Models are used to describe nature.