CHEMISTRY 3RDQ

• Democritus - Atoms are the building blocks of matter,

  the shape of an atom explain elements behavior.
• ATOMOS (400 BC) - Democritus
• John Dalton - Atom is a solid indivisible sphere.
• SOLID SPHERE (1803) - John Dalton
• J.J Thomson - Negative electrons are embedded in a sea of positive charges.
• PLUM PUDDING (1897) - J.J Thomson
• NUCLEAR (1911) - Ernest Rutherford
• Ernest Rutherford - Positive charges are located within a

  central nucleus.
• PLANETARY (1913) - Niels Bohr
• Niels Bohr - Electrons are restricted in circular orbits

  with different energy levels.
• QUANTUM (1926) - Erwin Schrödinger
• Erwin Schrödinge - Electrons are in clouds surrounding the

  nucleus, and this cloud is less dense.
• QUANTUM (1926) - Erwin Schrödinger
• ATOMIC ORBITALS - Electrons act like waves.
• ATOMIC ORBITALS - The exact location of electrons cannot be determined.
• ORBITALS - A region in an atom where there is a high probability of finding electrons
• ORBITALS - Atomic orbitals (s, p, d, or f)
• PRINCIPAL - Distance of the electron from nucleus
• AZIMUTHAL - Shape of the orbital
• MAGNETIC - Orientation of the orbital
• SPIN - Orientation of the electron spin
• ELECTRON CONFIGURATION NOTATION - The electron configuration of an element describes how electrons are distributed in its atomic orbitals.
• Elements in Group 8A also called as noble gases are the most stable elements in the periodic table and

  are thus nonreactive under ordinary conditions; hence, the description “inert”
• Except for helium with only two electrons in its orbital, noble

  gases--- with a general valence configuration of 𝑛𝑠^2np^2 --- have 8 valence electrons. Such octet configuration is the most stable arrangement an atom can have.
• The atoms of the other elements in the periodic table tend to achieve the configuration of the nearest noble gas by reacting with the same element or with other elements to form new compounds.
• This principle is referred to as the octet rule.
• In 1916 American chemist Gilbert Lewis (1875 – 1946) developed a system of representing the valence electrons of atoms using diagrams called Lewis electron–dot structures or Lewis structures
• A Lewis structure consists of a symbol of an element

  surrounded by one or more dots: each dot corresponds to a valence electron in an atom of an element. Only two dots are placed in each of the four sides.
• A dot is placed in each of the four sides of the element symbol before pairing with another as needed to represent all the valence electrons of the elements.
• There are no strict rules on which sides to pair up first so the dot symbol for oxygen may be written in several equivalent forms
• Metals have one to three valence electrons, which can be easily removed because of their relatively low ionization energy.
• Nonmetals having high electron affinity, can gain valence electrons to fill their s and p orbitals and form an octet.
• Electrons given off by a metal atom are gained by the nonmetal, forming ionic bond in the process.
• Ionic compounds generally exist between a metal and a nonmetal as a result of their high electronegativity difference
• Solid ionic compounds generally do not conduct electricity because their constituent particles are bound by strong

  ionic bond in a lattice. But when in a solution, the particles are dissociated and can move easily. This movement of ions allows the solution to conduct electricity.
• The ionic bonds that bind the ions are strong such that high energy is required to separate the ions and allow them to move freely and form a liquid and gas.
• Some ionic compounds can conduct electricity in their solid state and are called solid electrolytes.
• Ionic compound assumes a solid lattice, where the cations and anions are arranged in an alternating sequence, making the structure stable.
• Ionic compounds are generally hard because of their fixed and stable lattice. Most ionic compounds are also brittle. An external force applied to the crystal may distort its lattice, make like charges align, and then repel, causing the crystal to break.
• Because nonmetal atoms have relatively similar electronegativities, they tend to attract valence electrons equally (or almost equally) and just share them to achieve an octet (or duet)