Ionic and Covalent Bonding

Ionic and Covalent Bonding lon typically formed ЕВ 1 1 н 13 2 -l 14 в с Li Ве з- 2- 1l l O 1 I 18 15 Не N Ne 4 5 6 s Ar Са Sc Ti V Cr Mn Fe Со Ni Cu Zn Ga Ge As Se Kr Na Mg 3 к з+ 4 1 7 8 9 10 1 1 12 AI Si р Rb Sr у Zr Nb Мо Те Ru Rh Pd Ag Cd ln Sn Sb Те Cs Ва La Hf Та w Re 0s lr 1 Хе Pt Au Hg TI РЬ Bi Ро At Rn Fr Ra Ас Rf Db Sg Bh Hs Mt Uun Uuu Uub О = Weak nuclear attraction for valence electrons; tendency to form positive ions = Strong nuclear attraction for valence electrons; tendency to form negative ions = Strong nuclear attraction for valence electrons but valence shell is already filled; no tendency to form ions of either type Lewis Structures • The availability of electrons and needs of atoms in a molecule are tracked • Show how available valence e- are shared between atoms in a molecule • Can indicate either ionic and covalent bonding • The element symbol is imagined to have a box around it. The valence e- are distributed around the four sides of the box. • For the “a” group elements, the group number is the number of valence e-. • For, Al, a group IIIa element, there are 3 valence e-. Its Lewis structure is 3 Electron Configurations and Lewis Symbols The Octet Rule • Stable atoms tend to have full or exactly halffull sublevels. • Special stability is achieved in the noble gases, which have full sublevels. • The “octet rule”- atoms will lose or gain e- in order to have 8 e- surrounding them as have the noble gases. • H and He will need only 2 e-, thus follow the “duet rule”. 5 The Octet Rule – Rephrased • Atoms tend to gain, lose and/or share electrons in order to obtain a stable noble gas configuration in their valence electrons. • For elements 1-5 “duet” rule • For the rest of the elements “Octet” rule Ionic Compounds Ionic compounds form when oppositely charged ions are attracted to each other NaCl Resulting compound is electrically neutral Na+ Cl– (+1) + (–1) = 0 Sodium chloride Chemical Bonds - Ionic Ionic bonds form when atoms transfer valence electrons in the forming ions that are then attracted to each other. Metal - nonmetal bonds are ionic because: – metals have low ionization energies and easily lose e- to be stable – non-metals have higher electron affinities – the formation of the lattice stabilizes the ions. • Ionic crystals: exist in a 3-dimensional array of cations and anions called a lattice structure • Ionic chemical formulas: always written as empirical formula (smallest whole number ratio of cation to anion) • “Formula Unit” is the term used to describe the empirical formula of ionic compounds 8 Ionic Bonding is the TRANSFER of electrons from one element to another. Lattice Energy, U • Formation of gaseous ions from an ionic solid Lattice xy+ • AxBy(s)→xA (g) + yB (g) Compound Ions Energy (kJ mol−1) LiCl Li+ and Cl− 845 NaCl Na+ and Cl− 778 KCl K+ and Cl− 709 LiF Li+ and F− 1033 CaCl2 Ca2+ and Cl− 2258 AlCl3 Al3+ and Cl− 5492 CaO Ca2+ and O2- 3401 Al2O3 Al3+ and O2- 15,916 U vs. Bond Formation Energy • The formation of one mole of solid from gaseous ions (ionic bond formation) is numerically the same as the lattice energy • Na+(g) + Cl-(g) → NaCl(s) + 787 kJ • Since this is energy released, the value for this process would be –U • Smaller ions have greater attractive forces, as have those with higher charges q1q 2 U kr 11 Electron Configurations Ions 1. The first electrons to be lost by an atom or ion are always those from the shell with the largest value of n 2. As electrons are removed from a given shell, they come from the highest-energy occupied subshell first before any are removed from a lower-energy subshell. 3. Within a given shell, the energies of the subshells vary as follows: s p d f. 12 Electron Configurations Of Cations • Main Group metals lose the electrons in their highest energy subshell first to achieve the previously filled noble gas (the octet rule) • Group Ia: [Noble gas core]ns1 – Form 1+ ions to be isoelectronic with noble gas core element • Group IIa: [n.g.c.]ns2 – Forms 2+ ions • Group IIIa: [n.g.c.]ns2np1 – Forms 3+ ions 13 Electron Configuration of Cations • Main Group metals lose the electrons in their highest energy subshell first. Elements in group IIIa below Al also form 1+ ions. • Ga : [Ar] 4s2 3d104p1 - 1 e- → • Ga+ : [Ar] 4s2 3d10 - 2 more e- → • Ga3+ : [Ar] 3d10 14 Bonds forming lonic bonds formed Са 2+ Fluorine atom Calcium atom Fluorine atom Calcium fluoride, CaF 2 Fluorite lonic bonds formed Bonds forming Aluminum oxide, А1203 Aluminum atom Oxygen atom Sapphire