Access to Chemistry

1. Are you ready to learn? Lab notebook out and a pen No food out, drinks away Phones on silent and in your bag Bags and coats under bench or at the back. Access to Chemistry Learning aims: Carry out ionic and covalent practical Recall bonding between ions and atoms Introduce and define intermolecular and intramolecular bonding. News!

2. Ionic and covalent practical

3. Break 15 minutes!

4. Build a poster to show bonding • Matter is ‘held together’ by these forces or bonds • First Intramolecular - the bonding between atoms or ions • .

5. Metallic bonding • the bonding between metals

6. Metallic bonding • Between metals – metallic bonds – a crystalline structure (solid repeating pattern) comprised of metal cations (positive ions) with a sea of delocalised electrons (not fixed to any one point, but moving throughout the structure) • Properties of metals: shiny, conduct heat and electricity, can be drawn into wires (ductility) or hammered into sheets (malleability). • Generally solid at room temperature because bonds are metallic bonds are strong. • The greater the positive charge on the metal cation, the stronger the bond, as more valence (outer) electrons involved in bonding.

7. Covalent bonding Electron pairs hold the atoms together, existing as either discrete molecules or giant arrays of atoms (macromolecular)structures. May be polar or non-polar depending on electronegativity (the attraction of a nucleus for the bonding pair of electrons) • 1. small discrete molecules (solid, liquid or gas at room temperature)

8. Covalent bonding • 2. giant arrays of atoms (macromolecular) Solid at room temperature

9. Properties of covalent substances • low solubility in water, • low boiling / melting points, • no ions so don’t conduct electricity. • If the molecules are polar there will be greater solubility in water. (we will see why later)

10. Ionic bonding • exist as a large crystalline structure ( a repeating pattern) of anions (negative ions) and cations (positive ions). • Solid at room temperature due to strong ionic bonds

11. Properties of ionic compounds • high melting and boiling points, • conduct electricity when molten (melted) or when dissolved in water, due to the presence of ions. • They are brittle and soluble in water (polar solvent).

12. 4 states of matter Solid, liquid, gas and plasma

13. States of matterGAS • are far apart on average (not close packed) Particles • have rapid random movement • have no attractive forces between them

14. States of matterLIQUID • are close packed Particles • move more slowly than in gases, particles slide past each other • have strong attractive forces between them

15. States of matterSOLID • are close packed Particles • move by vibrating only • have very strong attractive forces between them

16. To change state requires or releases energy • melting boiling Solid liquid gas freezing condensing Some substance will go from solid to gas missing out the liquid stage this is called sublimation. What happens when changes of state occur? Atoms / ions or molecules gain enough heat energy to move faster (kinetic energy ) and break the weak bonds between them that hold them in that state.

17. At room temperature • Most metallic bonds, giant arrays of atoms (macromolecular) and ionic bonds are strong so substances exist as solids at room temperature. • Covalent bonds are equally strong, however we find these in all three states of matter. • Why?

18. Intermolecular forces • The forces between simple covalent molecules and noble gases atoms are called intermolecular forces.

19. Intermolecular forces (bonds) • 3 types: 1. London Dispersion forces • They are very weak but account for iodine being a solid. • The more electrons an atom has the stronger the forces. Instantaneous dipole Weak London dispersion forces between iodine molecules

20. δ+ δ- H Cl δ+ δ- H Cl δ+ δ- H Cl 2. Dipole-dipole interactions Stronger than London dispersion forces, occur between polar covalent molecules dipole-dipole attractive force (weak) covalent bond (strong) Both London dispersion forces and dipole-dipole forces are known collectively as Van der Waals forces.

21. H O H H O H x x O x x δ- H H δ+ δ+ 3. Hydrogen bonding in water Hydrogen bonds Similar to dipole-dipole but stronger. Stronger than either of the other 2 forces Occurs where there is hydrogen and other very electronegative atom such as nitrogen, fluorine and oxygen.

22. Hydrogen bonding in water Stretch & Challenge x 100 80 60 40 20 boiling point/oC period number 0 x 2 3 4 5 H2Te H2Se H2S H2O -20 x -40 x -60 x boiling point that water would have in the absence of hydrogen bonding (approx. -70oC) -80

23. Hydrogen bonding in proteins

24. Summary of bonding DECREASING STRENGTH • Ionic and covalent bonds • Metallic bonds • Hydrogen bonding • Dipole-dipole forces • London dispersion forces Intramolecular bonds (forces) – within molecules or crystalline structures. Intermolecular bonds (forces) – between molecules or noble gas atoms. If forces between molecules are weak, they will be easily overcome by heat

25. L London dispersion

26. Learning outcomes • Carry out ionic and covalent practical • Recall bonding between ions and atoms • Introduce and define intermolecular and intramolecular bonding. • Issue of assignment 2 – report ?

27. http://www.youtube.com/watch?v=cERb1d6J4-M

28. Periodic Table click to return