Download Homework, Ch.2 2.7 First, convert 1 cm to picometers. 2.10 You

Homework, Ch.2
2.7
First, convert 1 cm to picometers.
1 cm 
0.01 m
1 pm

 1  1010 pm
1 cm
1  1012 m
? He atoms  (1  1010 pm) 
1 He atom
1  102 pm
 1  108 He atoms
2.10
You identify an element by its atomic number. When it has different mass numbers, it is the same element,
but its isotopes.
2.11 Isotopes
2.12
X is the element, Z is the atomic number, and A is the mass number.
2.13
For iron, the atomic number Z is 26. Therefore the mass number A is:
A  26  28  54
2.14
The 239 in Pu-239 is the mass number. The mass number (A) is the total number of neutrons and protons
present in the nucleus of an atom of an element. You can look up the atomic number (number of protons)
on the periodic table.
Solution:
mass number  number of protons  number of neutrons
number of neutrons  mass number  number of protons  239  94  145
2.15
2.16
Isotope
No. Protons
No. Neutrons
3
2 He
4
2 He
24
12 Mg
25
12 Mg
48
22Ti
79
35 Br
195
78 Pt
2
1
2
2
12
12
12
13
22
26
35
44
78
117
Isotope
No. Protons
No. Neutrons
No. Electrons
15
7N
33
16 S
63
29 Cu
84
38 Sr
130
56 Ba
186
74W
202
80 Hg
7
8
7
16
17
16
29
34
29
38
46
38
56
74
56
74
112
74
80
122
80
23
11 Na
(b)
64
28 Ni
2.17
(a)
2.21
(a) a nonmetal
2.26
F and Cl are Group 7A elements; they should have similar chemical properties. Na and K are both Group
1A elements; they should have similar chemical properties. P and N are both Group 5A elements; they
should have similar chemical properties.
2.27
An atom is the smallest unit of an element which is represented as a single entity, eg., H
Molecule is more than one atom of the same element or a combination of different elements,
eg., H2, SO2
2.30
(a)Na+, (b) Cl- (c) NH4+ (d) NO3-
15
7N
(b) a metal
23
11 Na
(c) metalloid
11
5B
2.31
(a)
(b)
(c)
This is a polyatomic molecule that is an elemental form of the substance. It is not a compound.
This is a polyatomic molecule that is a compound.
This is a diatomic molecule that is a compound.
2.33
Elements:
Compounds:
2.35
Ion
No. protons
No. electrons
2.45
(a)
2.48
The molecular formula of ethanol is C2H6O
2.49
Compounds of metals with nonmetals are usually ionic. Nonmetal-nonmetal compounds are usually
molecular.
CN
Ionic:
Molecular:
N2, S8, H2
NH3, NO, CO, CO2, SO2
Na
11
10
(b)
Ca2
20
18
CH
(c)
Al3
13
10
C9H20
Fe2
26
24
I
53
54
(d)
F
9
10
S2
16
18
P2O5
(e)
O2 
8
10
N3 
7
10
BH3
LiF, BaCl2, KCl
SiCl4, B2H6, C2H4
2.57
(a)
(b)
(c)
(d)
(e)
(f)
(g)
sodium chromate
potassium hydrogen phosphate
hydrogen bromide (molecular compound)
hydrobromic acid
lithium carbonate
potassium dichromate
ammonium nitrite
2.59
(a)
(f)
RbNO2
KH2PO4
2.64
(a)
52
25 Mn
2.65
Uranium is radioactive. It loses mass because it constantly emits alpha () particles.
2.67
The number of protons  65  35  30. The element that contains 30 protons is zinc, Zn. There are two
fewer electrons than protons, so the charge of the cation is 2. The symbol for this cation is Zn2.
2.84
(a)
(b)
2.110
The mass number is the sum of the number of protons and neutrons in the nucleus.
(b)
(g)
(b)
K2 S
IF7
22
10 Ne
(c)
(h)
(c)
107
47 Ag
(h)
(i)
(j)
(k)
(l)
(m)
(n)
phosphorus trifluoride
phosphorus pentafluoride
tetraphosphorus hexoxide
cadmium iodide
strontium sulfate
aluminum hydroxide
sodium carbonate decahydrate
NaHS
(NH4)2SO4
(d)
(d)
(i)
127
53 I
Mg3(PO4)2
AgClO4
(e)
(e)
(j)
CaHPO4
BCl3
239
94 Pu
Ionic compounds are typically formed between metallic and nonmetallic elements.
In general the transition metals, the actinides, and the lanthanides have variable charges.
Mass number  number of protons  number of neutrons
Let the atomic number (number of protons) equal Z. The number of neutrons will be 1.2Z. Plug into the
above equation and solve for Z.
55  Z  1.2A
Z  25
The element with atomic number 25 is manganese, Mn., Mn with +2 charge is represented as Mn+2