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CHAPTER 2
Dr. Nizam M. El-Ashgar
Solution of Selected
Problems
General Chemistry A
2.2: There are three types of radiations:
1- Alph particles (): are positively charged particles.
2- Beta particles ( ): are negatively charged particles (electrons).
3- Gamma rays (): are high energy rays, have no charge.
2.10: Because all isotopes of the element have the same number of protons and vary
in the number of neutrons.
Atoms of the same element with different mass numbers called istopes.
A X:
Z
Z: is a symbol refers to the atomic number.
A: is a symbol refers to the mass number.
X: is a symbol refers to the atom of the element.
2.12:
The number of neutrons of 23994Pu = 239-94 = 145.
2.16:
a) Z = 74, A = 186 are for
186
74W.
b) Z = 80, A = 201 are for
201
80Hg.
2.19:
a) Nonmetals: Chlorine: Cl; Oxygen: O; Sulfur: S; Nitrogen: N.
b) Metals: Copper: Cu; Sodium Na; Iron: Fe; Magnesium: Mg.
c) Metalloids: Silicon: Si; Germanium: Ge; Arsenic: As; Antimony: Sb.
2.22:
a) Down a periodic group: The metallic properties increases and the non metallic
properties decreases fro example: group IVA: C is a nonmetal, Si and Ge are
metalloids but Sn and Pb are metals.
b) Across the periodic table: The metallic properties decreases from left to right while
the nonmetallic properties are increases for example: across the second period, we can
find Li and Be are metals, B is a metalloid but C, n, O, F, Ne are nonmetals.
1
2.29:
Nitrogen dioxide (NO2) and Dinitrogentetroxide (N2O4) are different compound have
different molecular formulas but the same empirical formula (NO2).
2.31.
A molecule: is an aggregate of at least two atoms in a definite arrangement held
together by chemical forces.
A compound : is a substance composed of atoms of two or more elements
chemically united in fixed proportions. H2 is a molecule of an element (hydrogen) but
it is not a compound. H2O (water) is a molecular compound.
Although the definitions appear to be similar the molecule is not necessary a
compound
1.32:
a) H2, O2
b) HCl, NO
c) O3, P4
d) H2SO4, CH4
2.34:
Molecular formula of ethanol is CH3CH2OH
2.35:
a) C2N2: CN.
b) C6H6: CH.
c) C9H20: C9H20.
d) P4H10: P2H5.
e) B2H6: BH3.
2.36:
a) Al2Br6: AlBr2.
b) Na2S2O4: NaSO2.
c) N2O5: N2O5.
d) K2Cr2O7: K2Cr2O7.
2
2.39:
Ion
Number of
Protons
Number of Ion
Electrons
Number of
Protons
Number of
Electrons
K+
19
18
Mn2+
25
23
Mg2+
12
10
C4-
6
10
Fe3+
26
23
Cu2+
29
27
Br-
35
36
2.43:
Compound
Name
Compound
g) NH4NO2
Name
a) Na2CrO4
Sodium chromate
Ammonium nitrite
b) K2HPO4
Dipotassium hydrogen h) PF3
phosphate
Phosphorous
trifluoride
c) HBr (gas)
Hydrogen bromide gas
i) PF5
Phosphorous
pentafluoride
d) HBr
water)
(in Hydrobromic acid
j) P4O6
Tetraphosphorous
hexaoxide
e) Li2CO3
Lithium carbonate
k) CdI2
Cadmium iodide
f) K2Cr2O7
Potassium dichromate
l) SrSO4
Strontium sulphate
m) Al(OH)3
Aluminum, hydroxide
3
2.45:
Compound
Formula
Compound
Formula
a) rubidium nitrate
RbNO3
f) boron
trichloride
BCl3
b) potassium sulfide
K2S
g) Iodine
heptafluoride
IF7
c) perbromic acid
HBrO4
h) ammonium
sulfate
(NH4)2SO4
d) magnesium phosphate Mg3(PO4)2
i) silver
perchlorate
AgClO4
e) calcium hydrogen
phosphate
j) iron (III)
chromate
Fe2(CrO4)3
CaHPO4
2.47
No. of protons of the atom = 65 - 35 = 30
The charge of the cation derived from the atom = 30 – 28 = +2.
The element is Zn and the cation symbol is Zn2+.
2.49
a) The neutral elements are: A, F and G.
b) The negatively charged ions are: B and E.
c) The positively charged ions are: C and D.
d) symbols are: A = B
B=N
C=K
D = Zn
E = Kr
F=B
2.52
a) The elements are: S8, O2, O, Cs, O3, S, P4.
b) compounds but not molecules: KBr, LiF.
4
G=F
c) The molecules but not compounds are: S8, O2, O3, P4.
d) The molecules and compounds are: SO2, N2O5, CH4,
2.60
The two liquids elements are:
Bromine, Br2: is a halogen (a non metal).
Mercury, Hg: is a metal.
2.65
The formula of magnesium oxide is MgO.
The formula of strontium oxide is : SrO.
2.68
a) Na and H: NaH.
b) B and O: B2O3.
c) Na and S: Na2S.
d) Al and F: AlF3.
e) F and O: OF2
f) Sr and Cl: SrCl2.
2.69
a) Br.
b) Rn.
c) Se
d) Rb
5
e) Pb.