L I D E. Chapter 3 Atoms and Elements. Chemistry in Focus 3rd edition Tro. An atom is the smallest identifiable unit of an element.

Transcription

1 Chemistry in Focus 3rd edition Tro Chapter 3 Atoms and lements The connection between the microscopic atom and the macroscopic element is the key to understanding the chemical world. 3 An atom is the smallest identifiable unit of an element. imilarities and differences on the atomic scale correlate with similarities and differences on the macroscopic scale.

2 4 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 +. Protons constitute a large part of the mass of an atom. Mass of a proton is.0 amu 5 Chemical ymbols ymbols are an abbreviation of the chemical name which can be based on: The nglish name for the element: hydrogen The Greek or atin name: ferrum Their place of discovery: europium The scientist honored by the naming: curium 6

3 7 lectrons A neutral atom has as many electrons outside its nucleus as protons within its nucleus. The opposing charges of protons and electrons holds electrons within a spherical region surrounding the nucleus. Atoms can lose and gain one or more electrons. 8 etermining Protons and lectrons 9 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 OTOP. Can be naturally occurring or man-made The sum of neutrons and protons in an atom is called the mass number of the atom.

4 0 Atomic Numbers and Mass Numbers pecifying an Atom Atoms can be described with a notation that includes atomic number (Z), mass number (A), and charge (C), with atomic symbol (X) in the form: A X C Z

5 3 4 5 Atomic Mass Atomic masses listed on the periodic table are weighted averages of the masses of each naturally occurring isotope for that element. Periodic aw 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.

6 6 7 8 Mendeleev published his table: While proposing that elements to be discovered would fill in gaps in his table. While proposing that some measured atomic masses were in error. As a summary of a large number of observations The underlying reasons for periodic behavior were to follow... the Bohr model and the quantum mechanical model The Bohr Model This is a MO that links electron behavior (microscopic) to the periodic law (macroscopic). Bohr iagrams/lectron Configurations Based on the behavior of electrons as particles lectron orbits pecified 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).

7 9 0 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.

8 3 4 eterminism and Quantum Mechanics pecifics 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 lements Also called groups Based on outer electron configurations Vertical columns Alkali metals Alkaline earth metals Chalcogens Halogens Noble gases lement Families

9 5 6 7 Metals, Nonmetals, and Metalloids Molecular lements ome 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 by weighing instead of counting. ince atoms are O small, the chemists dozen is called a mole and corresponds to

10 8 9 Avogadro s Number etermined 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.