The Structure of Matter: Compounds

1
The Structure of Matter Compounds Molecules

• Chemical bond - the attractive force that holds
  atoms or ions together
• Chemical structure the arrangement of bonded
  atoms or ions within a substance

2
Compounds Molecules 2

• Bond length average distance between nuclei of
  two bonded atoms
• Bond angle angle made by 2 bonds to the same
  atom

3
Compounds Molecules 3

• Whats the difference between compounds and
  mixtures?
• Figure out the relative s of atoms or ions in a
  compound from its chemical formula.

4
Compounds Vs. Mixtures 1

• Compounds have very different properties from the
  elements that make them.
• Here, elements lose solo properties when they
  bond together.

5
Compounds Vs. Mixtures 2

• Compounds same substances or different ones
  that are chemically bonded to each other like O2
  or the Hs Os in two molecules of water, 2H2O.
  
• Reactions that form these involve breaking of
  bonds rearrangement of atoms into new bonds.

6
Compounds Vs. Mixtures 3

• Mixtures different substances that are just
  placed together not bonded and still keep their
  individual properties.
• Compounds have chemical formulas which show the
  types numbers of atoms or ions that make up
  their simplest units.

7
Compounds Vs. Mixtures 4

• Compounds always have the same elements in the
  same combinations.
• Consider C6H12O6 for glucose, a product of
  photosynthesis.

8
Compounds Vs. Mixtures 5

• Anywhere that one finds a molecule of glucose in
  the universe, this compound will have 6 carbon,
  12 hydrogen 6 oxygen atoms all chemically
  bonded together.

9
Chemical Structure Bonding Within Compounds

• Chemical formulas dont show how atoms are
  connected
• In other words, they do not reveal bond angles
  bond lengths between atoms.

10
Bonding Within Compounds 2

• However, models do show bond lengths and angles.
• Structural formulas can show bond angles too but
  not bond lengths.

11
Models of Compounds 3

• Ball-and-stick models give an idea of bond
  lengths and bond angles.
• Space filling models show the space that bonded
  atoms occupy well.

12
Models of Compounds 4

• However, space filling models make it difficult
  to see the bond lengths and angles between the
  atoms in a compound.

13
Structure Affects Properties 1

• Network structure includes the same bond angles
  throughout the compound and multiple bonds on
  repeating centers.
• This results in strong solids with unusually
  strong bonds that take more energy to break.

14
Structure Affects Properties 2

• For example in quartz, 4 oxygen atoms bond each
  silicon atom at 109.5 angles.
• High melting points (mp) boiling points (bp)
  result from network structures b/c it takes more
  heat energy to break stronger bonds.

15
Structure Affects Properties 3

• Networks can be made of bonded positive and
  negative ions in cube shaped crystals.
• Molecular or covalent compounds have weaker bonds
  as a result lower melting boiling points.

16
Structure Affects Properties 4

• Ionic compounds bonds between ions where these
  charged atoms have given away or taken electrons.
• Covalent compounds bonds between atoms where
  these atoms share electrons.

17
Structure Affects Properties 5

• How do weaker bonds cause lower mp and bp?
• Different structures in molecular compounds
  result in different mp and bp even among grouped
  compounds.

18
Structure Affects Properties 6

• Consider Table 4-2 on page 113 and Figure 4-8 on
  page 114.
• Structure affects even the strength of
  attractions beween molecules.
• For example, intermolecular attraction between
  molecules of H20 is stronger than attraction
  between those of H2S, dihydrogen sulfide.

19
Structure Affects Properties 7

• What do the decreasing mp and bp for sugar
  (C12H22O11), H20 H2S in this order tell us
  about their relative attractions for each other?
  
• Rank them in order of least to greatest
  intermolecular attraction.

20
Structure Affects Properties 8

• Notice that sugar water have very different
  stuctures w/ expectedly different properties.
• However, water dihydrogen sul-fide have more
  similar structures than properties. Why is this?

21
Structure Affects Properties 9

• Hydrogen bonding extra strong intermolecular
  attractions between hydrogen and oxygen atoms in
  nearby compounds.