Key Area Homework

1. Key Area Homework answers

2. How are elements arranged in the Periodic Table? • In order of atomic number (number of protons in an atom of the element)

3. Categorise the first 20 elements according to bonding and structure • Metalliclattice– Li, Be, Na, Mg, Al, K, Ca • Covalent molecular – H2, N2, O2, F2, Cl2, P4, S8 and C (fullerenes) • Covalent network – B, C (diamond, graphite), Si • Monatomic – noble gases

4. What is the covalent radius of an atom? The size of an atom is measured by it’s covalent radius, the distance between the nucleus and it’s outer electrons.

5. Describe how covalent radii change across a period and down a group. Across a period we can see the covalent radius decreasing. Down a group we see the covalent radius increasing

6. What is meant by ionisation energy? The ionisation energy is the energy required to remove one mole of electrons from one mole of atoms in the gaseous state.

7. Na (g) Na+ (g) + e • Write the equation for the first ionisation energy of sodium.

8. Explain how ionisation energy changes across a period and down a group. Across a period from left to right ionisation energy increases This is due to the increase in atomic charge having a greater pull on the electrons and therefore more energy is required to remove electrons. Down a group ionisation energy decreases This is due to the outer electrons being further away from the nucleus and so the attraction is weaker and they are more easily removed.

9. What is electronegativity? Electronegativity is a measure of an atom’s attraction for the shared pair of electrons in a bond

10. Describe the trend in electronegativity value across a period and down a group. Across a period electronegativity increases Down a group electronegativity decreases

11. Draw a diagram explaining the bonding continuum for covalent and ionic bonds.

12. What is a covalent bond? • A bond in which a pair of electrons are equally shared

13. What is a polar covalent bond? • A bond in which a pair of electrons are shared but not equally

14. How is an ionic bond formed? • When electrons are transferred from a metal atom to a non-metal atom

15. What are Van der Waals’ forces? • Intermolecular forces – ie between molecules

16. What are London dispersion forces and when do they operate? • Weak forces of attractions between temporary dipoles in atoms of monatomic elements or molecules with pure covalent bonding when in the liquid or solid state

17. How are London dispersion forces formed? • By the temporary uneven distribution of electrons causing a temporary dipole

18. What is meant by a polar molecule? • a molecule which has polar bonds which are not symmetrically arranged leading to a permanent dipole in the molecule

19. What is meant by a permanent dipole – permanent dipole interaction? • Attraction between polar molecules

20. How do hydrogen bonds form between molecules? • If H is directly bonded to N O or F (very highly electronegative atoms)

21. Put the following type of bonds in order of strength (starting with the strongest). Covalent, hydrogen bonding, London dispersion forces, ionic. • Cov and ionic > H bonding> LDF

22. How can chemists predict the strength of the intermolecular forces that exist between molecules? • Decide whether they are LDF, dipole-dipole attractions or H bonds

23. Why do ammonia, water and hydrogen fluoride has higher than expected boiling points? • Have H bonding between the molecules (because H is attached to N, O or F) which is stronger than other intermolecular attractions so b pts are higher than expected

24. What properties of substances does hydrogen bonding affect? • H bonding affects Mpt. Bpt. Density, surface tension, viscosity