2011 Atoms, Bonds and Groups Jan

Question 1

Define the term relative atomic mass

Answer 1

• The (weighted) mean mass of an atom (of an element)
• compared with 1/12th (the mass)
• of (one atom of) carbon-12

Question 2

What is the 3-D shape of the 5s orbital

Answer 2

• Spherical/ sphere

Question 3

What is meant by the term ionic bonding

Answer 3

• (Electrostatic) attraction between oppositely charged

ions

Question 4

What is meant by the term electronegativity

Answer 4

• The ability of an atom to attract electrons

* In a covalent bond

Question 5

Molecules of BF3 contain polar bonds, but the molecules are non-polar. Suggest an explanation for this difference

Answer 5

• BF3 is symmetrical

* The dipoles cancel out

Question 6

State one use of calcium hydroxide in agriculture and suggest why the amount of calcium hydroxide used should not be in excess

Answer 6

• Used to neutralise acidic soil
• Excess will result in soils becoming too alkaline (to
sustain crop growth)

Question 7

Difference in observation of calcium with water and barium with water

Answer 7

• Idea of Ba having a quicker rate OR more vigorous

reaction

Question 8

Describe how van der Vaals forces arise

Answer 8

• Uneven distribution of electrons
• Creates an instantaneous dipole or temporary dipole
• Causes induced dipole(s) in neighbouring
molecules

Question 9

State and explain the trend in boiling points of chlorine, bromine and iodine

Answer 9

• Boiling points increase down the group
• Greater number of electrons/stronger intermolecular forces
• More energy needed to break intermolecular forces