Expressions Of Pj Problems
Ionic Compounds

Periodic Table

Ionic compounds are compounds formed by two or more ions. Many important compounds are ionic compounds.
(a) What are ions?
(b) Use the periodic table to predict the charge of the following elements:
(i) Mg, (ii) Al, (iii) K, (iv) S, (v) F.
(c) Use the periodic table to predict the formula and name of the compound formed by the following elements:
(i) Ga and F, (ii) Li and H, (iii) Al and I, (iv) K and S.
(d) Predict the chemical formula for the ionic compound formed by:
(i) Ca2+ and Br-, (ii) K+ and CO32-, (iii) Al3+ and C2H3O2- (iv) NH4+ and SO42-, (v) Mg2+ and PO43-.
(e) Which of the following are molecular compounds and which are ionic compounds?
(i) B2H6, (ii) CH3OH, (iii) LiNO3, (iv) Sc2O3, (v) CsBr, (vi) NOCL, (vii) NF3, (viii) Ag2SO4.
(f) Determine the chemical formulas that distinguish the following compounds from one another:
(i) calcium sulfide and calcium hydrogen sulfide (ii) hydrobromic acid and bromic acid (iii) aluminum nitride and aluminum nitrite (iv) iron (II) oxide and iron (III) oxide (v) ammonia and ammonia ion (vi) potassium sulfite and potassium bisulfite (vii) mercurous chloride and mercuric chloride (viii) chloric acid and perchloric acid.

The strings: S7P2A22 (Identity - Chemical Identity).

The math:
Pj Problem of Interest is of type identity (chemical identity).

Periodic Table

Electron Configurations

(a) The elements of the periodic table are charge neutral because numbers of positive charges (protons) equal numbers of negative charges (electrons). When some elements combine to form compounds, they do so by either donating or accepting electrons. The donation or acceptance of electrons changes the element's charge neutrality. Donors of electrons become positively charged (+) because they become electron deficient and now have more protons than electrons. Acceptors of electrons become negatively charged (-) because they become electron rich and now have more electrons than protons. An ion is an element that is positively or negatively charged. An ionic compound is a compound formed by ions. A positively charged ion is called a cation. A negatively charged ion is called an anion.

(b)Three regions in an atom determines its electron configuration: shell, subshell and orbitals. A shell is also called the principal quantum number or energy-level of an atom. It is usually denoted by the letter n. For example, n = 1 implies the first shell (shell or energy-level nearest the nucleus of the atom); n = 2 implies the second shell and so on. Energy increases with increasing n.
There are n subshells in the nth shell. The first subshell is called the s subshell, the second is called the p subshell, the third is called the d subshell, the fourth is called the f subshell, the fifth the g subshell and so on.
There are n2 orbitals in the nth shell. For example, when n = 2 (second shell), the number of subshells in the second shell is 2 and the number of orbitals is 4. The orbitals are the regions where the electrons of an atom are most likely to be found.
In general, a shell with principal quantum number n has n subshells. The nth subshell has 2n-1 orbitals which can hold a total of 2(2n-1) electrons.
The total number of electrons in the shell is the sum of all the electrons in all the orbitals of the shell's subshells. The total electrons in an orbital type can be expressed as: nxy where n is the number of the shell (energy-level or principal quantum number) containing the orbital type x, and y is the number of electrons contained in the orbital type x (s, p,d, f, are orbital types).
Max number of electrons in the s subshell = 2 (1 orbital), p subshell = 6 (3 orbitals), d orbital =10 (5 orbitals), f orbital = 14 (7 orbitals), etc.

(bi) From the periodic table and the electronconfiguration table:
Atomic number of magnesium (Mg) = 12, energy level, n = 3, 3s orbital filling,
So, electron configuration for magnesium (Mg) 3s orbital filling:
So, Mg has 2 donatable electrons in its valence shell
So magnesium ion = Mg2+.
(bii) Atomic number of aluminum (Al) =13, energy level, n=3
So, electron configuration for aluminum, 3p orbitals filling:
So, Al has 3 donatable electrons in its valence shell
So aluminum ion = Al3+.
(biii) Atomic number of potassium (k) 19, energy level = 4
Electron configuration for potassium, 4s orbital filling:
So, K has 1 donatable electron in its valence shell
So, potassium ion = K+.
(biv) Atomic number of sulphur (S) =16, energy level = 3
So, electron configuration for sulphur, 3p orbital filling:
So, S can accept 2 electrons in its valence shell
So, sulphur ion = S2-.
(bv) Atomic number of fluorine (F) =9, energy leve =2
So, electron configuration for fluorine, 2p orbital filling:
So, F can accept 1 electron in its valence shell
So, fluorine ion = F-.

(ci) Atomic number of gallium (Ga) = 31, enegy level =4
So, electron configuration for gallium, 4p orbital filling:
So, 3 donatable electrons
So,gallium ion =Ga3+
Fluorine ion = F-
So, 3 ions of fluorine will combine with 1 ion of gallium to form:
Gallium (III) Fluoride, GaF3.
(cii): lithium ion = L+, hydrogen ion = H-
Compound formed = LH = lithium hydride.
(ciii): aluminum ion = Al3+, iodine ion = I-
Compound formed = AlI3 = aluminum(III) iodide
(civ): potassium ion = K+, sulphur ion = S2-
Compound formed K2S = potassium sulfide.

(di): two bromine ions are needed for the calcium ion
compound = CaBr2.
(dii): two potassium ions are needed for the carbonate ions
compound form = K2co3 =
(diii): Al(C2H3O2)3
(div): (NH4)2SO4
(dv): Mg3(PO4)2

(e): Bondings between non metals more likely to be molecular compound while bondings between metals and nonmetals are more likely to be ionic.
So, (i) B2H6, (ii) CH3OH, (vi) NOCL, (vii) NF3 are molecular compounds.
So, (iii) LiNO3, (iv) Sc2O3, (v) CsBr, (iii) LiNO3, (iv) Sc2O3, (v) CsBr, are ionic compounds.

(fi): calcium sulfide = CaS; calcium hydrogen sulfide =Ca(HS)2
(fii) hydrobromic acid = HBr; bromic acid = HBrO3
(fiii) aluminum nitride = AlN; and aluminum nitrite = Al(NO2)3
(fiv) iron (II) oxide = FeO; iron (III) oxide = Fe2O3
(fv) ammonia = NH3; ammonia ion =NH4+
(fvi) potassium sulfite = K2SO3; potassium bisulfite = K2HSO3
(fvii): mercurous chloride = Hg2Cl2; mercuric chloride = HgCl2
(fviii): chloric acid = HClO3; perchloric acid = HClO4


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