C2 The Periodic Table

Question 1

C2.1 development of the periodic table

Answer 1

The periodic table of elements developed as chemists tried to classify the elements. It arranges them in an order in which similar elements are frouped together. The periodic table is so named because of the regularly repeating patterns in the properties if 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

C2.2 electronic structures and the periodic table

Answer 2

The atomic (proton) number of an element determines its position in the periodic table. The number of electrons in the outermost shell (highest energy level) of an atom determines its chemical properties. The group number in the periodic table equals the number of electrons in the outermost shell. The atoms of metals tend to lose electrons, whereas those of non-metals tend to gain electrons. The noble gases in group 0 are unreactive because of their very stable electron arrangements.

Question 3

C2.3 group 1 - alkali metals

Answer 3

The elements in group 1 of the periodic table are called the alkali metals. 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 the alkali metals increases going down the group.

Question 4

C2.4 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

2.5 Explaining trends

Answer 5

You can explain trends in reactivity as you go down a group in terms of the attraction between electrons in the outermost shell and the nucleus. This electrostatic attraction depends on: the distance between the outermost electrons and the nucleus, the number of pccupied inner shells of electrons, which provide a shielding effect, the size of the positive charge on the nucleus. In deciding how easy it is for atoms to lose or gain electrons from their outermost shell, thses three factors must be taken into account. The increased nuclear charge, due to extra protons in the nucleus, going down a group is outweighed by the other two factors. Therefore electrons are easier for the larger atoms to lose going down a group, and harder to gain going down a group.

Question 6

2.6 The transition elements

Answer 6

Compared with the alkali metals, transition elements have much higher melting points and densities. They are also 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 charge, in compounds that are often coloured. Transition elements and their compounds are important industrial catalysts.