📝 Periodicity

Task

🎧️ Listen to the recording and mind pronunciation of words.

Periods in the Periodic Table are rows of elements whose outermost electrons are in the same principal quantum shell. The atoms of neighboring members differ by one proton and one electron. As atomic number increases, the properties of the elements show trends which repeat themselves in each Period of the Periodic Table. These trends are known as Periodic Trends. A column of elements thus arranged is called a group.

Atomic radii decrease across a period due to increasing nuclear charge. This means electrons are pulled closer to the nucleus, making the atomic radius smaller. Positive ions are much smaller than their atoms. Negative ions are slightly larger than their atoms.

The first ionization energy of an element is the energy required to remove one electron from each of a mole of free gaseous atoms of that element. A high ionization energy means there is a high attraction between the electron and the nucleus and so more energy is needed to remove the electron The greater the number of protons, the greater the attraction of the electrons to the nucleus and the harder it is to remove the electrons Attraction falls off very rapidly with distance. An electron close to the nucleus will be much more strongly attracted than one further away. As the number of electrons between the outer electrons and the nucleus increases, the outer electrons feel less attraction towards the nuclear charge.This lessening of the pull of the nucleus by inner shells of electrons is called shielding. The first ionisation energy increases across a period because the nuclear charge increases but the shielding remains the same. Electronegativity increases across period due to increasing number of outer electrons.

Across a period, the structures of the elements change from giant metallic, through giant molecular to simple molecular. Group 18 elements consist of individual atoms. There is a gradual decrease in metallic character in crossing a period. Electrical conductivity increases from sodium to aluminium as the number of delocalized electrons per atom increases. Across a period, the oxides of Period 3 elements change from basic compounds with ionic bonding through to giant molecular in the centre of the period (Group 14) with silicon, going on to acidic covalently bonded simple molecules of the non-metal oxides. Aluminium oxide (in Group 13) is amphoteric, exhibiting both basic and acidic behavior. Across a period, the chlorides of Period 3 elements change from ionic compounds that dissolve in water to covalent compounds that are hydrolyzed by water, releasing fumes of hydrogen chloride and leaving an acidic solution.

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