Chapter 2: The periodic table

Question 1

Development of the periodic table

Answer 1

• Developed as chemists tried to classify the elements. It arranges them in an order in which similar elements are grouped together
• The periodic table is so named because of the regularly repeating patterns in the properties of elements
• Mendeleev’s periodic table left gaps for the unknown elements, which when discovered matched his predictions, and so his table was accepted by the scientific community

Question 2

Electronic structures and the periodic table

Answer 2

• The atomic number (no. of protons) of an element determines its position in the table
• The number of electrons in the outer shell determines its properties.
• The group number = no. of electrons on outer shell
• Atoms of metals tend to lose electrons, whereas non-metals tend to gain electrons
• The noble gases in group 0 are very unreactive because their outer shell is full of 8 electrons

Question 3

Group 1 - the alkali metals

Answer 3

• Their melting points and boiling points decrease going down the group
• The metals all react with water to produce hydrogen and an alkaline solution containing the metal hydroxide
• They form 1+ ions in reactions to make ionic compounds. These are generally white and dissolve in water, giving colourless solutions.
• The reactivity of these metals increases going down the group

Question 4

Group 7 - the halogens

Answer 4

• The halogens all form ions with a single negative charge in their ionic compounds with metals
• The halogens form covalent compounds by sharing electrons with other non-metals
• A more reactive halogen can displace a less reactive halogen from a solution of one of its salts
• The reactivity of the halogens decreases going down the group

Question 5

Explaining trends

Answer 5

• You can explain trends of reactivity as you go down the groups of the periodic table in terms of the attraction between electrons in the outermost shell and the nucleus
• This electrostatic attraction depends on:

  o	The distance between the outermost electrons and the nucleus 
  
  o	The number of occupied inner shells (energy levels) of electrons, which provide a shielding effect
  
  o	The size of the positive charge on the nucleus (called the nuclear charge)

• In deciding how easy it is for atoms to lose or gain electrons from their outer shell, these three factors must be taken into account: the increased nuclear charge, due to extra positions protons in the nucleus, going down a group is outweighed by the other two factors.
• Group 1 elements increase in reactivity as you go down the table whereas group 7 decreases as you go down the table. This is because the further the shells are from the nucleus, the less attracted they are to it. This means that it is easier for group 1 metals to lose their outer electron because it is not being ‘held onto that tight’. Whereas, for group 7 elements this make It harder for them to attract a new electron from other atoms.
• It is harder for bigger atoms to gain electrons but easier for them to lose electrons

Question 6

The transitions metals

Answer 6

• Compared with the alkali metals, transition metals have much higher melting points and densities. They are stronger and harder but are much less reactive
• The transition elements do not react vigorously with oxygen or water
• A transition element can form ions with different charges, in compounds that are often coloured
• Transition metals and their compounds are important industrial catalysts