Types of Solids

1. Types of Solids Intra V Inter

2. Type of bonding within the molecule Covalent Ionic Metallic Covalent Simple molecular solids with different intermolecular forces Intramolecular

3. Intermolecular • Forces holding holding molecules together • Van der Waals • Dipole-dipole • Hydrogen Bonding • These are the forces which are broken when a substance melts of changes state. These forces are used to explain physical properties of molecules.

4. Van der Waals • Weakest force holding molecules together. • Exist between atoms and NON-POLAR MOLECULES • The size of the force increases with size. • The bigger the atoms the bigger the force. • The more electrons the stronger the force.

5. Dipole-Diplole • Exist between POLAR molecules • Strength of the force increases with more Electronegative atoms. • Green Line represents the force

6. Hydrogen Bonding • This is the strongest form of intermolecular force in POLAR MOLECULES. • Attraction between hydrogen atoms and the lone pairs of either N, O or F atoms (the 3 most electronegative atoms) on a different molecule. They attract each other because of the difference in their electronegativities.

7.   So what should you look for to see if a substance has hydrogen bonding? • Look for either an O, N or F atom in the molecule. • Look for a hydrogen atom attached to any of the above named atoms. • TYPICAL PHYISCAL PROPERTIES • Unusually high melting and boiling points.

8. d+ d+ d+ d- d- d- H H H O O O H H H d+ d+ d+ Hydrogen Bonding Between the Lone pair on the O, N or F and the H on a neighbouring atom.

9. Hydrogen bonding in Water

10. Quick Test • For each of the molecules in the list, say what type of intermolecular forces hold them together: • hydrogen            • ethanoic acid    CH3C-O-H           • benzene  C6H6 • ammonia            • Iodine         O

11. Polar or Non-Polar • tetrachloromethane     CCl4 • carbon dioxide                • methane      CH4 • ethanol         CH3CH2OH                  • trichloromethane  CHCl3

12. Properties of Molecules • Generally • Non conductors of electricity • Low melting & boiling points • Why? Use FSEP – Force, Strength, Energy, Property • When changing from a solid to liquid the forces to be broken are the intermolecular forces between molecules. • These are relatively weak (van der waals etc) • Therefore require little energy to break • Hence a low melting point.

13. F S E P The intermolecular force of Van der Waals needs to be broken This is a weak force Therefore little energy is required to break Hence easily turns from solid to gas Why does I2 sublime?

14. F S E P H2O is polar & contains Hydrogen bonding whereas H2Se only contains Van der waals. Hydrogen Bonding is a stronger intermolecular force Therefore more energy is needed to break these bonds Hence a higher melting Point Why does H2O have a higher m.p than H2Se even though Se is a bigger atom?

15. Metallic Solids • Contain Metallic Bonding • Between metals • Explains their typical physical properties

16. Metallic bonding • Between one type of metal atom • Electrons form a ‘sea of delocalised electrons’ • Bond is between electrons and positive nuclei called electrostatic attraction. • The more valence shell of electrons the stronger the force of attraction

17. Metals Properties • Good electrical conductors. • Ductile, Malleable • Hard solids • Good heat conductors • High melting & boiling points

19. Electrical Conductors • Metals contain metallic bonding which has a sea of electrons • The electrons are mobile and able to carry current to complete the circuit

20. F S E P Metals contain metallic bonding, electrostatic attraction between sea of electrons and positive nuclei. This is very strong force of attraction It therefore requires a large amount of energy to break it. Hence metals have a high melting point Solids with High Melting points

21. Ionic Crystals • Exists between positive metal ions and negative non-metal ions. • This is a strong force of electrostatic attraction. • There are very many ionic bonds in an ionic compound such as sodium chloride, arranged in giant lattice structures. • Ionic compounds have high melting points and high boiling points.

22. NaCl Crystal

23. Properties • Many ionic compounds are soluble in water, but not all. Ionic compounds are polar as is water. • The solid crystals DO NOT conduct electricity because the ions are not free to move to carry an electric current. • However, if the ionic compound is melted or dissolved in water, the liquid will now conduct electricity, as the ion particles are now free.

24. F S E P Ionic compounds are made up of oppositively charged particles held together by electrostatic forces of attraction This force is a very strong attraction Therefore a large amount of energy are needed to break them Hence they have high melting points. Melting Points

25. I2 MgO Mg MgCl2 Cl2 HCl Identify the type of solid

26. Order of strength so far.. • Van der Waals • Dip- dip • Hydrogen Bonding • Ionic Bonding • Metallic Bonding

27. Giant Covalent Molecules • Exist in special covalently bonded substance • Consists of many Atoms bonded to atoms by a covalent bond in a giant structure

28. Diamond • Each carbon bonded to 4 other carbons • In a 3D structure • Similarly SiO2 – silica (sand)

29. Diamond Properties • High melting point – 4 very strong covalent bonds to break • Non- conductor of Electricity as no free ions or electrons • Non- polar therefore doesn’t dissolve in water • Hard as strong covalent bonds in all directions

30. Graphite • Each Carbon covalently bonded to 3 other Carbons • Arranged in layers weak van der waals holding them together • Free electrons not involved in bonding in between layers

31. Graphite Properties • High melting point as bonded by strong covalent bonds • Good conductor of electricity as delocalised electrons between layers • Non- polar therefore doesn’t dissolve in water • Soft as layers can slide over each as weak VdW forces between layers

32. Conclusion of Strength of forces holding solids together • Covalent – Giant Macromolecular • Metallic • Ionic Crystals • Simple molecules – Hydrogen Bonding - Dipole – Dipole - Van der Waals