IB Chemistry Topic 3 Pt. 2
The electronegativity of chlorine is higher than that of sulfur.
2Li + 2H2O ® 2LiOH + H2;
Explain how the first ionization energy of K compares with that of Na and Ar.
K less than Na because electron removed (from K) is from higher energy level/further from nucleus/in n = 4 compared to n = 3; this is more important than the extra 8 protons in K/OWTTE; increase repulsion by extra shell of electrons/greater shielding effect; so less strongly attracted by nucleus; K less than Ar because electron removed (from K) is from higher energy level/further from nucleus/ in n = 4 compare to n = 3; and has only one more proton; increase repulsion by extra shell of electrons/greater shielding effect; so less strongly attracted by nucleus;
Suggest why much more energy is needed to remove an electron from Na+ than from Mg+.
Mg greater than Na because (Mg has) greater nuclear charge/one more proton/12 protons compare to 11; electron removed is in same (main) higher energy level/shell; smaller (atomic) radius; so more strongly attracted by nucleus;
With reference to the types of bonding present in period 3 elements: (i) explain why Mg has a higher melting point than Na. (2) (ii) explain why Si has a very high melting point. (2) (iii) explain why the other non-metal elements of period 3 have low melting points.
Mg has greater nuclear charge/greater charge on cation/more valence e-/greater number of delocalized electrons/Na has lesser nuclear charge/lesser charge on cation/less valence e-/lesser number of delocalized electrons; stronger attraction between cation and delocalized/ free/valence electrons; 2 If neither mark scored, accept stronger metallic bonding in Mg for [1 max]. (ii) giant/network/lattice/macromolecular structure; many/strong covalent bonds (need to be broken); 2 (iii) (simple) molecular substances; weak van der Waals'/dispersion/London forces between molecules; 2 "Weak intermolecular forces" not sufficient for second mark
Describe the acid-base character of the oxides of the period 3 elements Na to Ar. For sodium oxide and sulfur trioxide, write balanced equations to illustrate their acid-base character.
Na, Mg: basic; Al: amphoteric; Si to Cl: acidic; Ar: no oxide; All four correct Na2O + H2O ® 2NaOH; SO3 + H2O ® H2SO4
Describe the acid-base character of the oxides of the period 3 elements Na to Ar. For sodium oxide and sulfur trioxide, write balanced equations to illustrate their acid-base character.
Oxides of: Na and Mg are basic; Al is amphoteric; Si to Cl are acidic; Ar has no oxide;
Table 6 of the Data Booklet lists melting points of the elements. Explain the trend in the melting points of the alkali metals, halogens and period 3 elements.
alkali metals: metallic bonding/a bed of cations in a sea of electrons; as radius increases down the group, valence electrons are further away from nucleus (and strength of metallic bonding decreases); halogens: non-polar/van der Waals' forces between molecules; as size increases van der Waals' forces increase (and melting point increases); period 3 elements: increase in melting points of metals (Na, Mg, Al) due to increase in number of valence electrons and decrease in size/the way atoms are packed as solids; Award mark just for "increased number of delocalized or valence electrons". silicon: network covalent solid (with very high melting point); Award mark also for "many or strong covalent bonds". P → Ar: simple molecular (atomic in case of Ar) substances with weak van der Waals' forces (and lower melting points); trend in P4, S8, Cl2, Ar due to size/mass of particles; 8 Award mark for "decreasing mass or size". Molecular formulae not necessary.
State and explain the trends in the atomic radius and the ionization energy (i) for the alkali metals Li to Cs.
atomic radius increases; because more full energy levels are used or occupied/outer electrons further from nucleus/outer electrons in a higher shell; ionization energy decreases; because the electron removed is further from the nucleus/increased repulsion by inner-shell electrons; 4 Accept increased shielding effect.
Table 8 of the Data Booklet gives the atomic and ionic radii of elements. State and explain the difference between (i) the atomic radius of nitrogen and oxygen.
atomic radius of N > O because O has greater nuclear charge; greater attraction for the outer electrons
the atomic and ionic radius of nitrogen.
atomic radius of P > N because P has outer electrons in an energy level further from the nucleus
State the electron arrangement of nitrogen and explain why it is found in period 2 and group 5 of the periodic table.
electrons in two energy levels/shells; five outer/valence electrons;
Explain the following statements. (a) The first ionization energy of sodium is (i) less than that of magnesium. ............................................................................................. ............................................................................................. ............................................................................................. ............................................................................................. (2) (ii) greater than that of potassium. ............................................................................................. .............................................................................................
greater nuclear charge/greater number of protons/atom radius g is smaller; stronger attraction (for electron);
Nitrogen is found in period 2 and group 5 of the periodic table. (i) Distinguish between the terms period and group.
second electron in Na removed from n = 2, whereas second electron in Mg removed from n = 3
Define the term ionization energy. ......................................................................................................................... ......................................................................................................................... (2) (ii) Write an equation, including state symbols, for the process occurring when measuring the first ionization energy of aluminium. ......................................................................................................................... (1) (b) The first ionization energies of the elements are shown in Table 7 of the Data Booklet. Explain why the first ionization energy of magnesium is greater than that of sodium. ...................................................................................................................................
the ability of an element/atom/nucleus to attract a bonding pair of electrons; 1 (b) electronegativity increases (along period 3 from Na to Cl); number of protons increases/nuclear charge increases/core charge increases /size of atoms decreases; 2 Do not accept greater nuclear attraction. (c) Cl2 is a stronger oxidizing agent/Chlorine's outer shell closer to nucleus; Cl2 has greater attraction for electrons/has a higher electron affinity; 2 Accept converse argument for Br2.
