Chemical bonds

• What does the octet rule state that explains why atoms bond?

  An atom bonds to have eight valence electrons to become stable.

  
• The diagram shows an electron shell model of a sodium atom. How would the model change as the atom forms bonds?

  The third shell would be empty so that the eight electrons in the second level would be outermost after the atom loses one electron.

  
• Atoms of which elements form bonds without satisfying the octet rule?

  helium (He) and hydrogen (H)

  
• Based on the location of nitrogen (N) on the periodic table, how many additional electrons does a nitrogen atom need in its valence shell to satisfy the octet rule when it forms bonds?


  three

  
• What is the most likely way in which an atom of magnesium (Mg) will satisfy the octet rule when it forms bonds?

  by losing two electrons

  
• Fluorine (F) and bromine (Br) are in the same group on the periodic table. How do atoms of these elements compare when they form bonds?


  Both a fluorine atom and a bromine atom gain one electron, and both atoms become stable.

  
• A force that holds atoms together is a chemical


  bond
• When sodium atoms (Na) and chlorine atoms (Cl) join to make sodium chloride, or table salt, they form an ionic bond. Using this information, which pair of elements is most likely to form an ionic bond?


  metal and nonmetal

  
• An atom of lithium (Li) forms an ionic bond with an atom of fluorine (F) to form lithium fluoride. How are the valence electrons of these atoms rearranged to form this bond and what proportion is needed?


  Electrons are transferred from the lithium atom to the fluorine atom. 1 lithium ion and 1 fluoride ion will form (LiF)

  
• Metal atoms tend to give away valence electrons when they bond with nonmetal atoms. What type of bond will form between the metal and nonmetal atoms and why does this bond form?


  An ionic bond will form because electrons are transferred.
• Lead is malleable, so it can be pounded into flat sheets without breaking. How does the bonding within lead help to explain this property?


  Metallic bonds involve many valence electrons shared by many atoms, so the bonds can move around as the metal is pounded.
• How many dots belong in the electron dot diagram of a boron (B) atom?


  three

  
• Sal drew the electron dot diagram of an aluminum atom. How should Sal correct his diagram?


  He should add a single dot to the symbol.

  
• Sunni drew an electron dot diagram of a silicon atom. In addition to changing the symbol to C, how would this diagram compare with an electron dot diagram of a carbon atom (C)?


  The same number of dots would appear in the diagram for carbon.

  
• What information on the periodic table is used to complete electron dot diagrams?


  The number of valence electrons is represented by the dots in the electron dot diagrams.
• The electron dot diagram shows the arrangement of dots without identifying the element. Which element symbol's could replace the question mark in the diagram?


  nitrogen (N), phosphorus (P), and arsenic (As)

  
• The electron dot diagram shows the arrangement of dots without identifying the element. Which element symbol's could replace the question mark in the diagram?


  oxygen (O), sulfur (S), selenium (Se), and tellurium (Te)

  
• Covalent Bond


  sharing of electrons (occurs between nonmetals)

  
• Polar Covalent Bond


  Unequal sharing/pulling of electrons between nonmetals (use electronegativity difference to determine if a bond is polar - if the EN difference is above 0.3 assume it is a polar covalent bond)

  
• Nonpolar Covalent Bond


  Equal sharing/pulling of electrons between nonmetals (if EN difference is 0, 0.1, or 0.2 assume it is a nonpolar covalent bond)

  
• Single Bond


  2 electrons (or 1 pair of electrons) being shared between 2 atoms (also called a sigma bond)

  
• Double Bond


  4 electrons (or 2 pairs of electrons) being shared between 2 atoms (made up of 1 sigma bond and 1 pi bond)

  
• Triple Bond


  6 electrons (or 3 pairs of electrons) being shared between 2 atoms (made up of 1 sigma and 1 pi bond)

  
• Hybridization (hybrid orbitals)


  sp, sp2, sp3

  
• linear shape (180 bond angle)


  central atom hybridization is sp

  
• bent shape (close to 109.5 bond angle)


  central atom hybridization is sp3

  
• trigonal planar shape (120 bond angle)


  central atom hybridization is sp2

  
• trigonal pyramidal shape (close to 109.5 bond angle)


  central atom hybridization is sp3

  
• tetrahedral shape (109.5 bond angle)


  central atom hybridization is sp3

  
• Polar Molecule (not the same as a polar bond)


  If on the central atom there are lone pairs of electrons (also called unshared electrons) or electrons that are not involved in bonding the molecule will be polar (regardless of the bonds). The overall pull is uneven.

  Trigonal pyramidal and bent shaped molecules will always be polar molecules.

  
• Nonpolar Molecule (not the same as a nonpolar bond)


  If on the central atom there are NO lone pairs of electrons (also called unshared electrons) the molecule will be nonpolar (regardless of the bonds). The overall pull is even.