GENCHEM

• Four numbers, called quantum numbers, were introduced to describe the characteristics of electrons

  and their orbitals.
• Orbitals that have the same value of the principal quantum number from a shell
• Orbitals within a shell

  are divided into subshells that have the same value of the angular quantum number.
• Subshells:

  1. s(sharp): l = 0
  2. p(principal): l = 1
  3. d(diffuse): l = 2
  4. f(fundamental): l = 3
• Quantum numbers:

  1. The principal quantum number (n) describes the size of the orbital or the energy level.
  2. The angular quantum number (l) describes the shape of the orbital. Orbitals have shapes that are the best described as spherical (l =0), polar (l =1), or cloverleaf (l =2).
  3. The magnetic quantum number (m), to describe the orientation in space of a particular orbital.
  4. The spin quantum number (ms)parameterizes the intrinsic angular momentum.
• The Aufbau principle, which assumes that electrons are added to an atom, one at the time, starting

  with the lowest energy orbital, until all of the electrons have been placed in an appropriate orbital.
• The Pauli Exclusion Principle is a quantum mechanical principle formulated by Wolfgang Pauli in

  1925. It states that no two identical fermions may occupy the same quantum state simultaneously. For

  electrons in a single atom, it states that no two electrons can have the same four quantum numbers, that

  is, if n, l and m, are the same, ms must be different such that the electrons have opposite spins.
• A paramagnetic electron is an unpaired electron.
• Diamagnetic atoms repel magnetic fields
• Ferromagnetism is an unusual property that occurs in only a few substances.
• Anti-ferromagnetism, type of magnetism in solids such as manganese oxide (MnO) in which adjacent

  ions that behave as tiny magnets (in this case manganese ions, Mn 2+) spontaneously align

  themselves at relatively low temperatures into opposite, or antiparallel, arrangements throughout the

  material so that it exhibits almost no gross external magnetism.
• atomic radius decreases across a period from

  left to right and increases down a given group.
• Anions are larger in size than their parent

  atoms because they have one or more additional electrons, but without an additional proton in the

  nucleus to help moderate the size.
• Cations are smaller than their parent atoms because they have lost

  electrons.
• The ionization energy, or ionization potential, is the energy required completely remove an electron

  from the gaseous atom or ion. The closer and more tightly bound an electron is to the nucleus, the more

  difficult it will be to remove, and the higher its ionization energy will be.
• Electron affinity reflects the ability of an atom to accept an electron. It is the energy change that occurs

  when an electron is added to a gaseous atom. Atoms with stronger effective nuclear charge have

  greater electron affinity.
• metallic bond is a type of chemical bond formed between positively charged atoms in which the free

  electrons are shared among a lattice of cations.
• Electrical conductivity


  Most metals are excellent electrical conductors because the electrons in the electron sea are free to move and carry charge
• Conductive nonmetals, molten ionic compounds, and aqueous ionic compounds


  Conduct electricity for the same reason—electrons are free to move around
• Thermal conductivity


  Metals conduct heat because the free electrons are able to transfer energy away from the heat source and also because vibrations of atoms (phonons) move through a solid metal as a wave
• Ductility


  Metals tend to be ductile or able to be drawn into thin wires because local bonds between atoms can be easily broken and also reformed. Single atoms or entire sheets of them can slide past each other and reform bonds
• Malleability


  Metals are often malleable or capable of being molded or pounded into a shape, again because bonds between atoms readily break and reform. The binding force between metals is nondirectional, so drawing or shaping a metal is less likely to fracture it. Electrons in a crystal may be replaced by others. Further, because the electrons are free to move away from each other, working a metal doesn't force together like-charged ions, which could fracture a crystal through the strong repulsion
•  Metallic luster: Metals tend to be shiny or display metallic luster. They are opaque once a certain

  minimum thickness is achieved. The electron sea reflects photons off the smooth surface. There is an

  upper-frequency limit to the light that can be reflected.
• Ionic Bond involves a metal and a non-metal ion or polyatomic ions such as ammonium through electrostatic

  attraction.
• Noble gases are the most stable elements in the periodic table. They have very high ionization energies and

  low electron affinity. To attain the stability of the structure of noble gases, elements tend to donate or accept

  their valence electrons.
• Metals donate their valence electrons and form cations.
• Nonmetals accept electrons and form anions
• Ionic compounds may also form with polyatomic ions.
• Properties

   High melting and boiling points - Ionic bonds are very strong - a lot of energy is needed to break them.

  So ionic compounds have high melting and boiling points.

   Conductive when liquid - Ions are charged particles, but ionic compounds can only conduct electricity if

  their ions are free to move. Ionic compounds do not conduct electricity when they are solid - only when

  dissolved in water or melted.
• The prefix co- means jointly, associated in action, partnered to a lesser degree, etc; thus a “covalent

  bond”, essentially, means that the atoms share “valence”.
• Covalent bonding is a common type of bonding, in which the electronegativity difference between the

  bonded atoms is small or nonexistent. Bonds within the most organic compounds are described as

  covalent.
• network solids are compounds containing covalent bonds that violate some of these "rules".

  Diamond, for example, consists of carbon atoms held together by covalent bonds in a crystalline

  structure. Network solids typically are transparent, hard, good insulators and have high melting points.
• Lewis structure

  This is also called electron-dot diagrams, is used to represent paired and unpaired valence (outer shell)

  electrons in an atom. This is proposed by Gilbert N. Lewis.
• Lewis symbol is a symbol in which the electrons in the valence shell of an atom or simple ion are

  represented by dots placed around the letter symbol of the element.
• A molecule is formed when atoms of the same or different elements combine. A molecule is the smallest

  particle of a substance that can normally exist independently.
• Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.
• To predict the shapes of molecules, the valence-shell electron-pair repulsion (VSEPR) theory is used.
• Bond Polarity or simply polarity, describes how equally bonding electrons are shared between atoms.
• polar molecule may be polar as a result of polar bonds or as a result of an asymmetric arrangement of non￾polar bonds and nonbonding pairs of electrons.
• non-polar compound may be non-polar because there is (almost) no polarity in the bonds or because of

  the symmetrical arrangement of polar bonds.