Chemical Bonding

Chemical Bonding

Energy Levels
1. Energy levels (shells)- the electrons that surround the nucleus of an atom
  1. 1st anergy level: 2 electrons
  2. 2nd energy level: 8 electrons
  3. 3rd energy level: 8 electrons
2. the period number of an atom(horizontal rows) correspond witht he number of energy levels in that atom
3. Energy level diagrams known as Bohr diagrams
4. how to determine # of electrons in an atom?- it is the same as the atomic #
5. Ions must have full energy levels
6. Aragon doesnt form ions bc its energy levels are aledeardy full
7. Atoms form ions to get full energy levels
Lewis Dot Diagram
1. Valence Electrons are in the outer shell--> determines charge
2. The # of the vertical column correspond with the # of valence e-
3. There are 4 valence orbitals for each atom
  1. Can hold between 0-2 electrons
  2. electrons occupy empty orbitals before pairing
4. # of protons & as # of electons is same as atomic #
5. # of neutrons= mass # - atomic #
Ionic Compounds
1. form from collision between elements results in TRANSFER of e-
2. one element loses an e- to form a cation (+), the other element gains e- forms anion (-)
3. electrostatic force- attracts cation and anion to each other
4. Properties
  1. 1) Do NOT consist of molecules (bonds of ions)
  2. 2) Bonds are strong (attractive forces are stronger than repulsive)
  3. 3) Have distinct properties (high melting/boiling point)
  4. 4) Liquid & dissolve salts, conduct electrce current (charged molecules are free to move)
  5. 5) They are hard&brittle->developes fracture (resists large force) (reapeating pattern forming layers if shifts into cleavage plane
5. How do we show an e- has transfer has occured?- square brakets w/ charge movement
6. what does the chemical formula chow us for ionic compounds?- simplest ratio of the compound cation to anion that exists
7. Crystal- an arrangement of ions in repeating unit
8. The arrangement of cations and anions depends on the charge and the number of the ions
9. Lattice- the specific ways in which atoms are arranged in an ionic compound
10. ion- the simplest repeating unit of a crystal structure
Electronegativity
1. electronegativity- the relative ability of an atom to attract a pair of binding e- in its valence level
2. each element is assigned an e-neg based on a scale developed by Linus Pauling
3. Matals have low e-neg
4. Non-metals have high e-negs
5. the DIFFERENCE in e-negs between the matal and non-metal that gives the bonds between their ionic character
6. Ex. oxygen: 3.5
Covalent compounds
1. Electrons
  1. 1 e- in an orbital is an unpaired/bonding electron, can be shared w/another atom
  2. 2 e- in an orbital non-bonding/lone pairs
    1. Will repell e- in other orbitals
    2. will NOT bind w/another atom
  3. Lewis dot diagrams show what e- are lone pairs and which can bond
2. Bonding capactiy
  1. the number of unpaired e- in an atom
  2. the maximum # of single covalent bonds that an atom can form
3. Formatopn of Covalent Bonds
  1. Octet rule
    1. atoms must be surrounded by 8 e- to have full valence shells
    2. Atoms must share 2 or more e-
  2. the shared e- belong to both valence levels of each atom
4. Lewis structure steps
  1. 1) Determine # of e-
  2. 2) The atom w/ lowest e-neg is the central atom
  3. 3) Distribute electrons so aech atom follows octet rule
  4. 4) repkace each pair of dots with a dash
  5. 5) Count # of electrons around each atom , must follow octet rule
    1. # of valence e- should be same from step 1
  6. 6) If structure is an ion, place brackets around and indicate charge
Multiple Bonds
1. Covalent bonds that has 2 or 3e- pairs by two atoms
  1. called double or triple bonds
Types of formulas
1. Empirical
  1. shows whole # ratio of atoms
2. Molecular
  1. shows actual # of atoms in compound
3. Lewis
  1. uses symbols to show e- sharing &transfer of stable valence octet
4. Structural
  1. shows which atoms are bonded&type of bond
5. Steriochemical
  1. structural formula to represent the compound in 3-D
  2. Linear- 2 bonding, most common Be or C, all on same plane
  3. Trigonal planar- 3 bonding, most common B or C, all on same plane
  4. Tetrahedral- 4 bonding, 2 on same plne 1 in front 1 behind, most common C or Si
  5. Trigonal planar- 3 bonding, 1 lone, 1 on plane 1 in front 1 behind 1 lone, common: N or P
  6. Bent- 2 bonding, 2 lone, 2 on plane 2 lone, common: O and P
  7. CARBON WILL NEVER HAVE A LONE PAIR
VSEPR
1. Parirs of e- that surround central atom of an ion arranged as far apart as possible to minimize electron-electron repulsion
2. Valence Shell Electron Pari Repulsion
3. Used to predict shape of ion
Polarity of Molecules
1. Dependant on 2 factors
  1. Bond Polarity
  2. Molecular shape
2. If molecule is only made of nonpolar bonds, then it is always nonpolar
3. If a molecule contains polar bonds it DOESNT always mean it is polar
4. If covalent bond is polar the e- are pulled to more e-neg atoms-> creates dipole bond
5. The shape of a molecule determines if dipole bonds will cancel out or create polar molecule
6. Nonpolar covalent: <0.5
7. Polar covalent: 0.5-2.1
8. Ionic: >2.1
9. If pulls dont all cancel out then it is a polar molecule
  1. All tetrahedrals that have same substituents are polar molecules
  2. All trigonal pyramidals are polar molecules
10. If all pulls cancel out then it is a nonpolar molecule
  1. bents are always nonpolar molecules

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