Chemistry for Dummies

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Chemistry for Dummies

• Smith
• 2005

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Atomic Mass (weight) vs Number

• Atomic of protons (usually of electons and
  neutrons same as well)
• Atomic Mass of protons of neutrons
• (Hydrogen has no neutrons so Atomic mass is also
  1)
• Mass measured in Daltons sometimes not a whole
  number

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Is an element reactive or not?

• Depends on whether or not an element needs to
  gain or lose electrons for stability
• Electrons stored in energy levels outside of
  nucleus-lower levels must be filled first
• Innermost level-only 2 electrons for stability
• Other energy levels8 electrons for stability

N needs 3 electrons in outer level for stability
O needs 2 electrons in outer level for stability
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Why dont some elements react or bond?

• Ex.-Noble gases like Helium and Neon
• Valence levels (last energy levels) are full so
  no need for them to react or bond to gain/lose or
  share electrons

He
2 electrons in innermost energy level
energy level is 'full'
Ne
8 electrons in valence energy levelfull
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Chemical reactions (bonding or breaking bonds)

• Reactions-occur when elements or molecules gain
  or lose electrons (bonds are made or broken)
• Single bond-1 electron from each element is
  shared (1pair)
• Double Bond-2 electrons from each element is
  shared (2 pairs)

H
C
H single bonds with C
They are each sharing 1 electron
H can't bind anymore-valence level feels like it
has 2 electrons
C valence level feels like it has 5 electrons-can
do 3 more single bonds
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What type of bonds can elements do?

• Hydrogen-only 1 single bond because it can only
  accept 1 more electron
• Carbon-4 single bonds, or 2 double bonds, or 1
  double with 2 single, or 1 triple and a single
  bond. Carbon needs to share 4 electrons for
  stability

H
C
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Who is most likely to bond together?

• Elements who can meet each others needs!
  (opposites attract or 2 that need equal sharing)
• Ex.-It would be easier for Li to LOSE 1 electron
  than gain 7, so it is a LOSER!
• Na-also needs to LOSE an electron-so it wont
  react with Li. Theyre both LOSERS!
• Fl-needs to GAIN 1 electron so it will react with
  Li or Na!

Li
Na
Fl
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Ionic vs. Covalent Bonding

• Ionic Bonding-one element needs to gain an
  electron, one element needs to lose one.
• IE-Na is a LOSER, Cl needs to gain one
• One element hogs the electron (Cl) from the
  other

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Ionic Bond-Unequal sharing

• Na and Cl are sharing an electron, but since Na
  is a LOSER and Cl needs to gain, the electron is
  usually pulled to Cl
• Since Proton is the same, now Na has a
  charge, and Cl is -

Cl 'hogs' the electron so Cl is more negative
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Ionic Bonds form Crystals

• Ionic Bonds are weaker
• One element is giving an electron while one is
  taking so there is little to hold 2 specific
  atoms together
• Ie-one Na atom may be attracted to several Cl at
  the same time and vise-versa-forms a crystal
  (salt!)
• Ionic bonds-weak so these are easily broken and
  dissolved

NaCl and Water-NaCl bonds broken
Result-NaOH and HCl
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The Covalent Bond

• Carbon needs to gain/share 4 electrons, Hydrogen
  needs to gain/share 1 electron, so they
  covalently share their one electron with each
  other
• Carbon will share with 4 Hydrogen to gain 4
  electrons

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Covalent Bond Continued

• Both elements involved have similar needs (need
  to gain or share a similar of electrons)
• Stronger bonds because of equal sharing

Notice electrons are 'shared' or equal
distribution
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Covalent Bonds can be unequal

• Even when elements are sharing electrons, one
  can have a stronger pull
• Ie-HF-Fluorine pulls the electrons more!
• Result-H has more charge, F is more -. This is
  a POLAR covalent bond

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Water is a Polar Covalent Bond

• H needs to share or gain one electron, O needs 2.
• O pulls the electrons away from H more, giving it
  a charge.
• H bonded to one O atom may be weakly attracted
  to another OHydrogen bonds! These are WEAK!
• H bonds between H in different water molecules
  makes water stick together!

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Nonpolar Covalent Bonds

• Carbon needs to gain/share 4 electrons, Hydrogen
  needs 1
• Both have ½ full valence levels so they equally
  pull shared electrons!
• Since nonpolar molecules have no reason to react
  with anything else, they dont react or mix with
  polar molecules! (Think oil and water!)

No charges because sharing is equal
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Comparing Ionic, polar covalent, and nonpolar
covalent
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