CIE AS Chemistry Period 3 Notes PDF

Head to www.savemyexams.com for more awesome resources CIE AS Chemistry Your notes 9.1 Periodicity of Physical Properties of the Elements in Period 3 Contents Physical Properties of the Period 3 Elements Str...

Head to www.savemyexams.com for more awesome resources CIE AS Chemistry Your notes 9.1 Periodicity of Physical Properties of the Elements in Period 3 Contents Physical Properties of the Period 3 Elements Structure & Bonding of the Period 3 Elements Page 1 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Physical Properties of the Period 3 Elements Your notes Describing Physical Properties of the Period 3 Elements Elements in the periodic table are arranged in order of increasing atomic number and placed in vertical columns (groups) and horizontal rows (periods) The elements across the periods show repeating patterns in chemical and physical properties This is called periodicity Arrangement of elements in the periodic table Page 2 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Elements are arranged by increasing atomic number from left to right Atomic radius Your notes The atomic radius is the distance between the nucleus and the outermost electron of an atom The atomic radius is measured by taking two atoms of the same element, measuring the distance between their nuclei and then halving this distance In metals, this is also called the metallic radius and in non-metals, the covalent radius Atomic radius The atomic radius gives a measure of the size of atoms Atomic radii of Period 3 elements table Period 3 element Na Mg Al Si P S Cl Ar Atomic radius 0.157 0.136 0.125 0.117 0.110 0.104 0.099 - (nm) Graph of atomic radii across Period 3 Page 3 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes There is a decrease in atomic radii of Period 3 elements across the period Across the period, the atomic radii decrease This is because the number of protons (the nuclear charge) and the number of electrons increases by one every time you go an element to the right The elements in a period all have the same number of shells (so the shielding effect is the same) This means that as you go across the period the nucleus attracts the electrons more strongly pulling them closer to the nucleus Because of this, the atomic radius (and thus the size of the atoms) decreases across the period Explaining why atomic radius decreases across Period 3 Page 4 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The diagram shows that across Period 3, the elements gain extra electrons in the same principal quantum shell Ionic radius The ionic radius is the distance between the nucleus and the outermost electron of an ion Metals produce positively charged ions (cations) whereas nonmetals produce negatively charged ions (anions) The cations have lost their valence electrons which causes them to be much smaller than their parent atoms This is because there are less electrons, which also means that there is less shielding of the outer electrons Going across the period from Na+ to Si4+ the ions get smaller due to the increasing nuclear charge attracting the outer electrons in the second principal quantum shell nucleus (which has an increasing atomic number) The anions are larger than their original parent atoms because each atom has gained one or more electrons in their third principal quantum shell This increases the repulsion between electrons, while the nuclear charge is still the same, causing the electron cloud to spread out Going across P3- to Cl-, the ionic radii decrease as the nuclear charge increases across the period and fewer electrons are gained by the atoms (P gains 3 electrons, S 2 electrons and Cl 1 electron) Page 5 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Ionic radii of ions of Period 3 elements table Period 3 ion Na+ Mg2+ Al3+ Si4+ P3– S2– Cl– Ar Your notes Ionic radius 0.095 0.065 0.050 0.041 0.212 0.184 0.181 No data (nm) Graph of ionic radii across Period 3 ions Ions of Period 3 elements with increasing positive charge (metals) and increasing outer electrons across the period Explaining why ionic radius changes across Period 3 Page 6 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The diagram shows the electron configuration of the ions of Period 3 elements and their relative sizes Melting point Melting points of the elements across Period 3 table Period 3 element Na Mg Al Si P S Cl Ar Melting point 371 923 932 1683 317 392 172 84 (K) Graph of melting points across Period 3 Page 7 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes There is a general increase in melting point from Na to Si, followed by a sharp drop to the lower melting points of P to Ar A general increase in melting point for the Period 3 elements up to silicon is observed Silicon has the highest melting point After the Si element, the melting points of the elements decrease significantly Electrical conductivity Electrical conductivity refers to how well a substance can conduct electricity Unlike the melting points, the electrical conductivity of the Period 3 elements shows a clear trend Going across the period, the electrical conductivity of the elements decreases significantly Initially there is an increase in the electrical conductivity from Na to Al and then this decreases across the remaining elements Page 8 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Trends in electrical conductivity across Period 3 table Period 3 element Na Mg Al Si P S Cl Ar Your notes Electrical conductivity 0.218 0.224 0.382 2 x 10-10 10-17 10-23 - - (S m-1) Page 9 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Structure & Bonding of the Period 3 Elements Your notes Explaining Physical Properties of the Period 3 Elements Melting point Melting points of the elements across Period 3 table Period 3 element Na Mg Al Si P S Cl Ar Melting point 371 923 932 1638 317 392 172 84 (K) Graph of melting points across Period 3 Page 10 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes There is a general increase in melting point from Na to Si, followed by a sharp drop to the lower melting points of P to Ar The above trends can be explained by looking at the bonding and structure of the elements Bonding and structure of the Period 3 elements table Period 3 element Na Mg Al Si P S Cl Ar Bonding Metallic Metallic Metallic Covalent Covalent Covalent Covalent - Giant Giant Giant Giant Simple Simple Simple Simple Structure metallic metallic metallic molecular molecular molecular molecular molecular Page 11 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The table shows that Na, Mg and Al are metallic elements which form positive ions arranged in a giant lattice in which the ions are held together by a 'sea' of delocalised electrons around them The structure of metals Your notes Metal cations form a giant lattice held together by electrons that can freely move around The electrons in the ‘sea’ of delocalised electrons are those from the valence shell of the atoms Na will donate one electron into the ‘sea’ of delocalised electrons, Mg will donate two and Al three electrons As a result of this, the metallic bonding in Al is stronger than in Na This is because the electrostatic forces between a 3+ ion and the larger number of negatively charged delocalised electrons is much larger compared to a 1+ ion and the smaller number of delocalised electrons in Na Due to this, the melting points increase going from Na to Al Si has the highest melting point due to its giant molecular structure in which each Si atom is held to its neighbouring Si atoms by strong covalent bonds P, S, Cl and Ar are non-metallic elements and exist as simple molecules (P4, S8, Cl2 and Ar as a single atom) The covalent bonds within the molecules are strong, however, between the molecules, there are only weak instantaneous dipole-induced dipole forces It doesn’t take much energy to break these intermolecular forces Therefore, the melting points decrease going from P to Ar (note that the melting point of S is higher than that of P as sulphur exists as larger S8 molecules compared to the smaller P4 molecule) Page 12 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Electrical conductivity The electrical conductivity decreases going across the Period 3 elements Your notes Trends in electrical conductivity across Period 3 table Period 3 element Na Mg Al Si P S Cl Ar Electrical conductivity 0.218 0.224 0.382 2 x 10-10 10-17 10-23 - - (S m-1) Going from Na to Al, there is an increase in the number of valence electrons that are donated to the ‘sea’ of delocalised electrons Because of this, in Al there are more electrons available to move around through the structure when it conducts electricity, making Al a better electrical conductor than Na Due to the giant molecular structure of Si, there are no delocalised electrons that can freely move around within the structure Si is therefore not a good electrical conductor and is classified as a semimetal (metalloid) The lack of delocalised electrons is also why P and S cannot conduct electricity Examiner Tip Intermolecular forces are forces between molecules Intramolecular forces are forces within a molecule Page 13 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers