ionic bonding ,lewis dot structures,electronegativity

why do we care abt chemical bonding?

• the structure of molecules basically determines their function

  • metabolism = chemical reactions on reactants done by enzymes

  • DNA transcription= protein attaches to DNA to start this process

  • how does the protein/enzyme know which reactant is connect one for it or where to go?

• structure of these molecules is the reason for this process

  • structure comes from bonding of the atoms together

types of chemical bonds:

• bonds form bw atoms to form molecules

  • molecules form bc atoms that make them up are more stable than individuals atoms

3 types of chemical bonds:

• metal w/non metal: ionic bond

  • electrons actually transferred from non metal to metal

• non metal w/non-metal:covalent bond

  • sharing of electrons

• metal w/ metal

  • sharing “sea” of electrons

properties of NaCl (sodium chloride):

• forms colorless crystal that is cubic and are hard and brittle

• high Mp (802 degrees)

• conducts electricity when melted (but not in solid- so not metallic or like graphite)

simple ionic compounds:

• contain a metal and a non metal (eg. Na (left side metal) Cl (right side non metal))

  • has one element with low electronegativity (metal)

  • has one element with high electronegativity(non metal)

• metals form cations, configurationnon metals form anions

  • each ion typically achieves noble gas congfiguration

  • why? trade off bw energy required to gain or lose electrons and stabilization of the system when ionic bonds are formed

• ionic compounds are neutral

sodium chloride:

• what color is Na+(cation +)?

  • purple (smaller one)

  • cations get small and shrink bc of the imbalance of protons pulling on electrons

• each Cl- is surrounded by Na+ ions

• each Na+ is surrounded by 6 Cl- ions

cations:

• positively charged

• smaller than corresponding atom (protons > e-= protons imbalance)

• simple cations form when metals lose electrons (ie elements with low electronegativity) (Na 3s1 →3s0 => [NE]

• charge usually corresponds to loss of electrons back to “core” but not bc this is more stable loss of electrons always requires energy

• why do cations form then? (Na+=Cl- → much more stable)

  • be highly charged ions form stronger bonds-which are more stable

anions:

• negatively charged

• larger than corresponding atom

• simple anions formed when non metals gain electrons (ie elements w high electronegativity)

• charge usually corresponds to gain of electrons to the next filled (sub) shell (ie noble gas configuration)

what charge do u expect on :

1. K (metal/cation +1) +1

2. Mg (metal/cation) +2

3. AL (metal /cation) +3

4. S (nonmetal/anoin) -2

5. Br (non-metal/anion) -1

an atom has a valence configuration of S2 P3.what ion will it form in an ionic compound?

-3

* transition metal ions always form a 2+ ion (and often others as well)