3 - Perodicity

• Elements in the periodic table are arranged in terms of increasing atomic number.
• Periods are the horizontal rows, containing elements with the same outer shell.
• Groups are the columns, containing elements with the same number of valence electrons.
• The first ionisation energy is the minimum energy required to remove an electron from a gaseous atom.
• Electronegativity is a relative measure of the attraction an atom has for a shared pair of electrons when it is covalently bonded to another atom.
• Both the atomic radius and ionic radius increase down the group, as there are more electron shells.
• MnO2 is a catalyst in the decomposition of H2O2.
• V2O5 is a catalyst in the Contact process.
• Fe is a catalyst in the Haber process.
• Ni is a catalyst in the conversion of alkene to alkane (hydrogenation).
• Co is a catalyst in vitamin B12.
• Pd and Pt are catalysts in catalytic converters.
• The 1st ionisation energy decreases down the group, as the outer electron is further away and there is more shielding of charge, requiring less energy to remove the electron.
• Electronegativity decreases down the group, as the atoms get bigger, there is more shielding of charge, decreasing the atom’s ability to attract electrons.
• The melting point in group 1 decreases down the group, as atoms get larger, there is more shielding of charge, the strength of the metallic bond decreases.
• The melting point in group 7 increases down the group, as the diatomic molecules of gas get bigger, greater attractive intermolecular van der Waals forces are present.
• Elements in the same group tend to have similar chemical properties, which are determined by the valence electrons.
• All of the alkali metals react exothermically with water to form an alkaline solution, and they also react readily with the halogens to form halide salts.
• The reactivity of the alkali metals increases down the group, with the more reactive halogens (higher in the group) able to oxidise less reactive ions.
• Atomic radius decreases across period 3, as electrons are being added to the same main energy level, but the proton number increases, attracting the outer shell closer to the nucleus, resulting in a lower atomic radius.
• Ionic radius decreases from Na to Al, then jumps, then decreases from P to Cl, as cations (positive) are smaller than their parent atom, since they have one less shell, and anions have more electrons than their atoms, making them larger.
• 1st ionisation energy generally increases across the period, as the smaller atomic radius requires greater attraction, making it harder to remove an electron.
• Electronegativity increases across the period, as the smaller atomic radius results in electrons being closer to the attraction of the nucleus.
• The period 3 elements tend to lose their metallic character across the period, with Na to Al forming ionic oxides, Si forming a macromolecular covalent oxide, and P to Cl forming covalent oxides.