1. Unit 1: Structure and Properties of Matter
4.8 Structure and Properties of Solids

2. Types of Solids Ionic Solids : metal and nonmetal
Metallic Solid: two metals
Molecular Solid: two nonmetals
Covalent Network: metalloids/carbon

3. Ionic Crystals
anions and cations are attracted together in CRYSTAL LATTICE
each anion surrounded by cations and vice versa
Ex: NaCl (salt), MgO (used in antacid tablets)

4. Crystal Lattice exists in three dimension
ionic substance held together by STRONG electrostatic attractions in all three dimensions
bonds are directional
lattice is composed of ions
no molecules in ionic compounds, referred to as formula units

5. Physical Properties of Ionic Compounds
Hard, brittle crystalline solids
Relatively high melting and boiling points
Do not conduct electricity when solid
Conduct electricity when molten or in aqueous solution
Soluble in water

6. Metallic Crystals
atoms are packed closely together in 3 dimensions (CLOSE-PACKED LATTICE)
metals have low ionization energies
so the valence electrons become DELOCALIZED amongst (shared by) all the atoms
no electrons belong to a particular atom, free to move throughout metal

7. Metallic Bonding
atoms have lost valence electrons, are positively charged (CATIONS)
attraction of positive ions for mobile electrons provides force that holds structure together
a lattice of positive ions filled by a mobile ‘sea’ of valence electrons

8. Physical Properties of Metals
attraction is between ions and mobile electrons, not between ions themselves
this means that layers of ions can slide past each other without breaking any bonds
means that metals are MALLEABLE and DUCTILE
if atoms are different sizes (in ALLOYS), it is harder for layers to slide
alloys are usually harder than pure metals

9. Physical Properties of Metals
delocalized electrons are free to move from one side of lattice to the other and can carry an electric current
metals are good CONDUCTORS of both electricity and heat
strength of bond between metals depends on how many electrons each atom shares
MP of Potassium is 337 K
MP of Calcium is 1123 K
MP of Scandium is 1703 K
strength also depends on how far from the nucleus the sea of electrons are
going down a group, the melting points will decrease

10. Molecular Crystals covalent bonds result in molecules
the covalent bonds holding molecules together (intramolecular) are strong, the forces between molecules (intermolecular) are much weaker
these weaker intermolecular forces lead to properties
generally soft in solid state, do not conduct electricity, more soluble in non-polar solvent than in water, have low melting and boiling points
Examples: iodine, sulfur, ice

11. Covalent Network Solids
giant, three dimensional covalent structure
look at the allotropes of carbon and silicon dioxide
ALLOTROPES : different forms of an element that exist in the same physical state

12. Allotropes of Carbon diamond (a) graphite (b)
C60 Fullerene (Buckyball) (d)
Londaleite (c)
C540 (e)
C70 (f)
amorphous carbon (g)
carbon nanotube (h)

13. Diamond
each carbon is joined to 4 other carbons in the tetrahedral shape
extremely strong structure!
all intramolecular bonds
explains high MP, BP and exceptionally hard structure

14. Graphite comprises a giant covalent network in 2 dimensions
each layer has C atoms bonded to 3 other C atoms
each layer is very strong
between the layers, only weak van der Waals forces hold the layers together

15. Graphite
distance between the sheets is quite large and the forces between very weak
so layers can slide over each other easily
often used as lubricant
layers are easily rubbed off on paper - why it is used in ‘lead’ pencils
can conduct electricity due to delocalized electrons

16. Fullerene
approximately spherical molecule made up of five- and six-membered C ring
C60 resembles a soccer ball
there is a small amount of delocalized electrons but not enough to strongly conduct electricity

17. Fullerene
behaves as an electron deficient molecule and readily accepts electrons
is a molecular molecule and can dissolve in some non-polar solvents
lower MPs than diamond or graphite

18. Silicon forms 4 covalent bonds almost identical structure to diamond
found in crystalline quartz
Shares the same chemical formula as glass but doesn’t form crystalline structure

19. Lab Review
Purpose
Hypothesis
Materials
Procedure
Observation Tables

20. Homework
Pg.254#1-9
Reminder: Solids Design Lab tomorrow