HOMEWORK 04
1. What What is a Lewi Lewis s dot dot symb symbol ol? ? To what what elem elemen ents ts does does the the symbol mainly apply? It is a way to represent chemical formulas, you use the symbol of the element and the electrons of valence to represent the relationships among the elements that form a compound. It is mainly applied for Alkali Alkaline, ne, alkalin alkaline e earth, earth, metals metals of transi transitio tion n non-met non-metals als and noble noble gases. (Chang, 2!"
2. Us Use e the the seco second nd membe ember r of each each group group from from Group Group 1A to Group A to show that the number of !alence electrons on an atom of the element is the same as its group number.
#he
number of
electrons of valence has increased according to the respective group number ". Write Write Lewis dot symbols symbols for atoms atoms of the following following elemen elements# ts#
$a% &e' $b% (' $c% )a' $d% Ga' $e% *' $f % &r' &r' $g% +' $h% ,' $i% As' $ -% .
/. Accordin According g to the following following isoelectr isoelectronic onic serie# serie# +a 01' g02' Al 0" . Which ion is the biggest? $a%! is the biggest because the atomic rate decreases according to the families from left to right. ri ght. (Chang, 2!" . 34plain 34plain what what an ionic ionic bond is. It is the electrostatic attraction between two elements, that involves a comple complete te transf transfer erenc ence e of electr electrons ons of valenc valence, e, ending ending electr electrica ically lly charged. #heir most common structure are crystals, (such as common salt". #hey tend to ioni&e in presence of water producing a'ueous solutions. (Chang, 2!"
5. 34plain 34plain how ioni6atio ioni6ation n energy and electron electron a7nity a7nity determine determine whet whethe her r atom atoms s of elem elemen ents ts will will com ombi bine ne to fo form rm ioni ionic c compounds. #he elements with low ioni&ation energy are more likely to form cations, and a high electron anity determines if an element could
)AC*+ */0C1* */0C1*
receive electrons to form anions, then, the electrons transference is easier in element with low ioni&ation energy and high electron anity.
(Chang, 2!" .
+ame 8!e metals and 8!e nonmetals that are !ery li9ely to form ionic compounds. Write formulas for compounds that might result from the combination of these metals and nonmetals. +ame these compounds. $a, i3 +e, Ca, 4r 5, Cl, I, 4, #e $a5 sodium 6uoride, iCl lithium chloride, +e4, beryllium sulphide,
4rI2 strontium iodide, Ca#e calcium telluride. :. +ame one ionic compound that contains only non;metallic
elements. Ammonium chloride $17Cl <. +ame one ionic compound that contains a polyatomic cation and a polyatomic anion ($17"2C*89 Ammonium Carbonate 18:*79 :hosphoric Acid 1=. 34plain why ions with charges greater than " are seldom found in ionic compounds. #he elements with high ioni&ation energy are unlikely to form ions, so the transference of more than three electrons, involves an e;penditure of high 'uantities of energy and the compound tends to be more unstable. (Chang, 2!" 11.
What is the ad!antage of using the term >molar mass
when we discuss ionic compounds? Ionic compound doesn
conducting? (a" 4olid, (b" molten (that is, melted", (c" dissolved in water. 0;plain your answers. =hen an ionic compound is dissolved in water it is divided in its ions, which are electrically charged and can conduct electricity.
4o the
answer is C.
1".
&eryllium forms a compound with chlorine that has the
empirical formula &e)l2. @ow would you determine whether it is an ionic compound? $The compound is not soluble in water%. #he subtraction between their radioactive values is generally a way to determine if this compound is ionic or covalent, where if the result is >2 it is an ionic compound. #he solid structure also, in which, the )AC*+ */0C1*
ionic compound is common presented in a cubic form. (Chang,
2!" 1/.
Gi!e
the
empirical
formulas
and
names
of
the
compounds formed from the following pairs of ions# $a% b 0 and ,;' $b% )s0 and B*/ 2;' $c% Br20 and +";' $d% Al"0 and B2;. I ubidium Iodide, Cs24*7 Cesium sulphate, 4r8$2 4trontium $itride, Al248 aluminium sulphide. !?./se ewis dot symbols to show the transfer of electrons between the following atoms to form cations and anions9 (a" $a and 5, (b" @ and 4, (c" +a and *, (d" Al and $.
15.
Write the Lewis dot symbols of the reactants and
products
in
the
following
reactions.
$irst
balance
the
eCuations.%
1.
or each of the following pairs of elements' state
whether the binary compound they form is li9ely to be ionic or co!alent. Write the empirical formula and name of the compound# $a% , and )l' $b% g and . a" Iodine chloride9 Cll, covalent b" g529 magnesium 6uoride, ionic
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1:.
or each of the following pairs of elements' state
whether the binary compound they form is li9ely to be ionic or co!alent. Write the empirical formula and name of the compound# $a% & and ' $b% ( and &r. a" +5 +oron tri6uoride9 Covalent b" @+r :otassium +romide9 Ionic 1<.
What is lattice energy and what role does it play in the
stability of ionic compounds? attice energy is the measure that shows how stable are ionic compounds, also dened as the necessary energy to divide a ionic bond, then, the energy used to ioni&e a compound and the energy used by the anion when it capture the electrons must be lower than the lattice energy to obtain a stable compound, that is the reason because elements cannot lose more or less than the electrons they should, producing the ionic compound that we actually know. (Chang, 2!" 2=. 34plain how the lattice energy of an ionic compound
such as ()l can be determined using the &orn;@aber cycle. *n what law is this procedure based? #he +orn-1aber cycle is based on the 1ess law, and we can use it to calculate lattice energy, relating it with ioni&ation energy, electron anity, among other properties. 5irst measure ne energy re'uired to sublimate the @, second the energy necessary to ioni&e the molecular Cl, third, the resultant energy of ioni&e the @, fourth the necessary energy to Boin the electrons to the anion, this total we subtract from the enthalpy of the overall reaction, and the result is the lattice energy. (Chang, 2!" 2!.Calculate the lattice energy of calcium chloride given that the heat of sublimation of Ca is !2! k)mol and D1Ef (CaCl2" F - GH? k)mol. (4ee #ables .2 and .8 for other data." !. Cas Cag F!2! k)mol 2. Cl2 2Cl F272. k)mol % 8. Ca Ca % e F?H.? k)mol % 2% Ca Ca % e F!!7? k)mol 7. 2(Cl % e Cl " F-JH k)mol 2% ?. Ca % 2 Cl FK D1Eoverall F-GH? k)mol !%!%8%7%?F D1Eoverall ?F2!H? k)mol 22. Use an e4ample to illustrate each of the following terms#
lone pairs' Lewis structure' the octet rule' bond length.
)AC*+ */0C1*
ewis structure
represents the
valence
electrons
of chemical
elements and how it could get related to others.
Atoms get stability when their more e;ternal layer is complete with electrons (with e;ception of 1e and 1" so they form diLerent types of bond to gain that stability.
In a molecule the distance between the nuclei of each atom is called bond length and it may vary.
=hen only an electron is shared by each atom it is called lonely pair
(Chang, 2!" 2".
)ompare
the
properties
of
ionic
compounds
and
co!alent compounds. #he structures Boined by ionic bond are solid, have high melting points, present cubic assemblies, their unions are strong and can form strong electrolytes, while the molecules composed by covalent bonds can be li'uid, gas or solid at room temperatures, do not have the same structure, have low melting points and are weak or nonelectrolytic substances. (Chang, 2!" 27. The following Lewis structures for $a% @)+' $b% ) 2@2' $c% Bn*2'
$d% &"' $e% @*' $f % @)*' and $g% + " are incorrect. 0;plain what is wrong with each one and give a correct structure for the molecule. (elative positions of atoms are shown correctly."
A9 $itrogen octet incomplete. +9 1ydrogen cannot form double bonds C9 4n
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octet was incomplete.
M9 + does not have ? electrons of valence
09 6uorine cannot receive 2 electrons
59 o;ygen octet is not
N9
$
complete
has
ve
electrons
of
Oalence (Chang, 2!"
2.
34plain why the bond enthalpy of a molecule is usually
de8ned in terms of a gas;phase reaction. Why are bond; brea9ing processes always endothermic and bond;forming processes always e4othermic? In the gas phase is seldom that the surrounding molecules could interfere in the division of a molecule of the product and alter the net energy necessary to divide it. #he molecule structure needs energy to be broken, otherwise could be easily destroyed, ergo, an e;tra energy will be necessary to destroy a chemical bond. And based on the rst thermo dynamical law, if the destruction involves absorption of energy the creation must releases it. (Chang, 2!"
25.
@ow is the geometry of a molecule de8nition and why is
the study of molecular geometry important? #he geometry of a molecule is dened by its three-dimensional structure, specically, the position of the atoms in it, as the length and angles among them. It is important because the molecule structure outline how its properties will be. (Chang, 2!" 2. De8ne dipole moment. What are the units and symbol
for dipole moment? It is the 'uantity to measure the polarity of a bond, it is e;pressed by the formula M =Q∗r
=here is the product of the charges and r the distance between them. Its unit is the Mebye. (Chang, 2!"
&ibliography Chang, . (2!". Chemistry (! 0dition". $ew Pork9 cNraw-1ill.
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