Chapter 4:- Atomic Structure And Chemical Bonding Flashcards
(804 cards)
1
Q
What is the definition of an atom?
A
An atom is made up of a nucleus (protons and neutrons) with associated electrons; characterized by mass number and atomic number.
2
Q
What is the electron distribution rule?
A
The electron distribution in the orbits follows the 2n rule and is governed by the octet rule.
3
Q
What are isotopes?
A
Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons.
Examples include hydrogen, carbon, and chlorine.
4
Q
What is an electrovalent bond?
A
An electrovalent bond is formed through the transfer of electrons from one atom to another, resulting in the formation of charged ions.
Examples include NaCl, MgCl2, and CaO.
5
Q
What is a covalent bond?
A
A covalent bond is formed when two atoms share electrons to achieve a full outer shell.
Examples include hydrogen, chlorine, oxygen, nitrogen, hydrogen chloride, water, ammonia, carbon tetrachloride, and methane.
6
Q
Who first proposed the idea of the smallest unit of matter?
A
Maharshi Kannada in the 6th Century B.C. in India proposed the idea of the smallest unit of matter, called paramanus.
7
Q
What does the term ‘atom’ mean?
A
The term ‘atom’ comes from the Greek word ‘atomos’, meaning indivisible.
8
Q
What are the main postulates of Dalton’s atomic theory?
A
- Matter consists of very small and indivisible particles called atoms. 2. Atoms can neither be created nor destroyed. 3. Atoms of an element are alike in all respects. 4. Atoms of an element combine in small numbers but differ from atoms of other elements to form molecules. 5. Atoms of one element combine with atoms of another element in a simple ratio to form molecules of compounds. 6. Atoms are the smallest units of matter that can take part in a chemical reaction.
9
Q
What did Faraday demonstrate in 1833?
A
Faraday demonstrated that the flow of electricity is due to the flow of charged particles.
10
Q
Who discovered the electron?
A
J. J. Thomson is credited with the discovery of the electron, a negatively charged particle.
11
Q
Who discovered protons and neutrons?
A
E. Goldstein discovered protons, and James Chadwick discovered neutrons.
12
Q
What are the fundamental particles of an atom?
A
The fundamental particles of an atom are electrons, protons, and neutrons.
13
Q
What is radioactivity?
A
The processes of transforming one elementary substance into another.
An atom is the smallest possible unit of an element.
14
Q
What happens when a small piece of zinc is ground into smaller pieces?
A
All pieces show properties of zinc until they reach a stage where they cannot be further subdivided into particles exhibiting properties of zinc.
15
Q
Who discovered electrons?
A
William Crookes, a British scientist.
16
Q
What happens to gases at low pressure when a high voltage is applied?
A
They become good conductors of electricity and flow from cathode to anode in the form of rays called cathode rays.
17
Q
What is a discharge tube?
A
A glass tube fitted with two metal plates known as electrodes, one connected to the positive terminal (anode) and the other to the negative terminal (cathode).
18
Q
What are the properties of cathode rays?
A
- They travel from the cathode to the anode in straight lines.
- They cause a greenish-yellow fluorescence on a soda-glass screen.
- They are affected by electric fields, indicating they carry a negative charge.
- They produce X-rays when striking hard metallic targets like tungsten.
- They penetrate through matter.
19
Q
What are negative charged particles called?
A
Electrons are negatively charged particles.
20
Q
What is the mass of an electron compared to a hydrogen atom?
A
The mass of an electron is 1/1837 the mass of a hydrogen atom.
21
Q
What is the charge of an electron?
A
An electron carries a unit negative charge of magnitude 1.602 x 10^-19 coulombs.
22
Q
What is the size of an electron?
A
The radius of an electron is less than 10^-10 m.
23
Q
Does the charge and mass of an electron change with different materials?
A
The charge and mass of an electron remain constant regardless of the material of the cathode or nature of the gas in the discharge tube.
24
Q
What are atoms composed of in terms of charge?
A
Atoms are electrically neutral, containing both negatively charged electrons and positively charged particles.
25
What are positively charged subatomic particles called?
Positively charged subatomic particles are called protons.
26
What are anode rays?
Anode rays consist of positively charged particles traveling from the anode towards the cathode.
27
What are the properties of anode rays?
1. Anode rays travel in a straight line.
2. They consist of minute material particles and produce mechanical effects.
3. They are made up of positively charged particles.
4. They are deflected by electric and magnetic fields in a direction opposite to cathode rays.
5. They produce fluorescence on a zinc sulphide screen.
6. Their charge to mass ratio differs from gas to gas.
28
What is the charge of a proton?
A proton possesses a unit positive charge of +1 (plus one) of the value 1.602 x 10^-19 coulombs.
29
What is the mass of a proton?
The mass of a proton is the same as that of a hydrogen atom (1 a.m.u., which is 1837 times the mass of an electron).
30
What are negative charged particles called?
Electrons are negatively charged particles.
31
What is the mass of an electron compared to a hydrogen atom?
The mass of an electron is 1/1837 the mass of a hydrogen atom.
32
What is the charge of an electron?
An electron carries a unit negative charge of magnitude 1.602 x 10^-19 coulombs.
33
What is the size of an electron?
The radius of an electron is less than 10^-10 m.
34
Does the charge and mass of an electron change with different materials?
The charge and mass of an electron remain constant regardless of the material of the cathode or nature of the gas in the discharge tube.
35
What are atoms composed of in terms of charge?
Atoms are electrically neutral, containing both negatively charged electrons and positively charged particles.
36
What are positively charged subatomic particles called?
Positively charged subatomic particles are called protons.
37
What are anode rays?
Anode rays consist of positively charged particles traveling from the anode towards the cathode.
38
What are the properties of anode rays?
1. Anode rays travel in a straight line.
2. They consist of minute material particles and produce mechanical effects.
3. They are made up of positively charged particles.
4. They are deflected by electric and magnetic fields in a direction opposite to cathode rays.
5. They produce fluorescence on a zinc sulphide screen.
6. Their charge to mass ratio differs from gas to gas.
39
What is the charge of a proton?
A proton possesses a unit positive charge of +1 (plus one) of the value 1.602 x 10^-19 coulombs.
40
What is the mass of a proton?
The mass of a proton is the same as that of a hydrogen atom (1 a.m.u., which is 1837 times the mass of an electron).
41
Where does the proton reside in an atom?
The proton resides in the central part of an atom, i.e., in the nucleus.
42
What is a proton?
A proton is a subatomic particle having a mass of 1 amu, equal to that of a hydrogen atom, and has a unit positive charge.
43
How is a proton denoted?
It is denoted as P, where the superscript represents its mass (1 amu) and the subscript represents one unit positive charge.
44
How is a proton formed?
A proton is formed by the loss of an electron from a hydrogen atom.
45
What are anode rays?
Anode rays consist of the positive residues left when electrons are knocked out of the atoms of gases in a discharge tube.
46
Where do cathode rays originate from?
Cathode rays originate from the metals or electrodes that constitute the cathode.
47
What model did J.J. Thomson propose in 1904?
J.J. Thomson proposed the 'plum pudding' model of the atom.
48
What are the key features of the plum pudding model?
1. An atom is a sphere of uniform positive charge with electrons embedded in it. 2. The total positive charge equals the total negative charge, making the atom electrically neutral. 3. The mass of an atom is uniformly distributed.
49
What are the limitations of the plum pudding model?
The model failed to address the concept of a central nucleus, could not explain the stability of atoms, and did not provide insights into electron arrangement or chemical bonding.
50
What experiment did Lord Rutherford conduct in 1911?
Rutherford directed a stream of alpha particles towards a very thin gold foil.
51
What were the observations from Rutherford's gold foil experiment?
1. Most alpha particles passed straight through the foil. 2. Some alpha particles were slightly deflected. 3. Very few alpha particles were deflected by large angles or completely bounced back.
52
What model did Rutherford propose based on his observations?
Rutherford proposed the Rutherford's Atomic Model.
53
What is an alpha particle?
An alpha particle is a doubly charged helium ion (He) consisting of 2 protons and 2 neutrons.
54
What observation do heavy metals like platinum show with alpha particles?
Heavy metals such as platinum will show the same observation with alpha particles as shown by gold foil.
55
What happens when light nuclei like lithium are used with alpha particles?
Fast moving alpha particles may push the light nucleus aside and may not be deflected back.
56
What does Rutherford's atomic model state about the structure of an atom?
The atom contains a large empty space (extra-nuclear space), allowing most alpha particles to pass through without deviation.
57
What is located at the center of the atom according to Rutherford's model?
A positively charged mass known as the nucleus, which contains the entire mass of the atom.
58
What is the nature of the nucleus in Rutherford's atomic model?
The nucleus is the densest part of the atom and contains protons, as evidenced by the deflection of positively charged alpha particles.
59
How does the size of the nucleus compare to the size of the atom?
The size of the nucleus is very small compared to the size of an atom, as most alpha particles pass straight through the gold foil.
60
Where do electrons revolve in an atom according to Rutherford's model?
Electrons revolve around the nucleus at large distances from each other and from the nucleus in circular orbits.
61
What is the overall charge of an atom?
An atom as a whole is electrically neutral, as the total positive charge of the nucleus is balanced by the total negative charge of the electrons.
62
What is a key similarity between Rutherford's atomic model and the solar system?
Rutherford's model is similar to the solar system, with the nucleus at the center and electrons revolving around it.
63
What is the main drawback of Rutherford's atomic model?
The comparison of electrons with planets is a drawback, as moving charged particles should radiate energy and spiral into the nucleus.
64
What would happen if Rutherford's model were accurate regarding electron stability?
If accurate, the atom would be highly unstable, and matter would not exist in the form we know.
65
What did Rutherford's model fail to explain?
It failed to explain the stability of an atom and the distribution of electrons around the nucleus.
66
Who proposed an alternative atomic model in 1913?
Niels Bohr, a Danish physicist, explained the causes of the stability of the atom in a different manner.
67
What observation do heavy metals like platinum show with alpha particles?
Heavy metals such as platinum will show the same observation with alpha particles as shown by gold foil.
68
What happens when light nuclei like lithium are used with alpha particles?
Fast moving alpha particles may push the light nucleus aside and may not be deflected back.
69
What does Rutherford's atomic model state about the structure of an atom?
The atom contains a large empty space (extra-nuclear space), allowing most alpha particles to pass through without deviation.
70
What is located at the center of the atom according to Rutherford's model?
A positively charged mass known as the nucleus, which contains the entire mass of the atom.
71
What is the nature of the nucleus in Rutherford's atomic model?
The nucleus is the densest part of the atom and contains protons, as evidenced by the deflection of positively charged alpha particles.
72
How does the size of the nucleus compare to the size of the atom?
The size of the nucleus is very small compared to the size of an atom, as most alpha particles pass straight through the gold foil.
73
Where do electrons revolve in an atom according to Rutherford's model?
Electrons revolve around the nucleus at large distances from each other and from the nucleus in circular orbits.
74
What is the overall charge of an atom?
An atom as a whole is electrically neutral, as the total positive charge of the nucleus is balanced by the total negative charge of the electrons.
75
What is a key similarity between Rutherford's atomic model and the solar system?
Rutherford's model is similar to the solar system, with the nucleus at the center and electrons revolving around it.
76
What is the main drawback of Rutherford's atomic model?
The comparison of electrons with planets is a drawback, as moving charged particles should radiate energy and spiral into the nucleus.
77
What would happen if Rutherford's model were accurate regarding electron stability?
If accurate, the atom would be highly unstable, and matter would not exist in the form we know.
78
What did Rutherford's model fail to explain?
It failed to explain the stability of an atom and the distribution of electrons around the nucleus.
79
Who proposed an alternative atomic model in 1913?
Niels Bohr, a Danish physicist, explained the causes of the stability of the atom in a different manner.
80
What are the main postulates of Bohr's atomic model?
1. Electrons revolve around the nucleus in fixed orbits called shells or energy levels, each associated with a fixed amount of energy.
2. While revolving in an orbit, an electron neither loses nor gains energy.
3. An electron can jump to the next orbit upon gaining energy and vice versa.
## Footnote
For convenience, these energy levels are labelled K, L, M, N, etc.
81
What is the K shell in Bohr's model?
The K shell is the orbit closest to the nucleus, has the least amount of energy, and contains K electrons.
82
What is the significance of neutrons in an atom?
Neutrons are neutral particles found in the nucleus of an atom, discovered by Chadwick in 1932.
83
What is the mass of a neutron?
The mass of a neutron is approximately 1.675 × 10^-24 g (1 amu).
84
How do neutrons behave in a magnetic or electric field?
Neutrons are not deflected by any magnetic or electric field, proving that they are electrically neutral.
85
What are the three subatomic particles in an atom?
1. Electrons: negatively charged particles found outside the nucleus.
2. Protons: positively charged particles found in the nucleus.
3. Neutrons: electrically neutral particles found in the nucleus.
86
What are the differences between Dalton's atomic theory and modern atomic theory?
1. Dalton's theory states atoms are indivisible; modern theory states atoms are divisible into subatomic particles.
2. Dalton's theory states atoms cannot be created or destroyed; modern theory states they can be created and destroyed by nuclear fusion and fission.
3. Dalton's theory states atoms of an element are alike; modern theory acknowledges isotopes.
4. Dalton's theory states atoms combine in small whole numbers; modern theory allows for larger numbers in organic compounds.
87
What is an alpha particle?
An alpha particle consists of two protons and two neutrons, equivalent to a helium atom that has lost both its electrons.
88
What are the main postulates of Bohr's atomic model?
1. Electrons revolve around the nucleus in fixed orbits called shells or energy levels, each associated with a fixed amount of energy.
2. While revolving in an orbit, an electron neither loses nor gains energy.
3. An electron can jump to the next orbit upon gaining energy and vice versa.
## Footnote
For convenience, these energy levels are labelled K, L, M, N, etc.
89
What is the K shell in Bohr's model?
The K shell is the orbit closest to the nucleus, has the least amount of energy, and contains K electrons.
90
What is the significance of neutrons in an atom?
Neutrons are neutral particles found in the nucleus of an atom, discovered by Chadwick in 1932.
91
What is the mass of a neutron?
The mass of a neutron is approximately 1.675 × 10^-24 g (1 amu).
92
How do neutrons behave in a magnetic or electric field?
Neutrons are not deflected by any magnetic or electric field, proving that they are electrically neutral.
93
What are the three subatomic particles in an atom?
1. Electrons: negatively charged particles found outside the nucleus.
2. Protons: positively charged particles found in the nucleus.
3. Neutrons: electrically neutral particles found in the nucleus.
94
What are the differences between Dalton's atomic theory and modern atomic theory?
1. Dalton's theory states atoms are indivisible; modern theory states atoms are divisible into subatomic particles.
2. Dalton's theory states atoms cannot be created or destroyed; modern theory states they can be created and destroyed by nuclear fusion and fission.
3. Dalton's theory states atoms of an element are alike; modern theory acknowledges isotopes.
4. Dalton's theory states atoms combine in small whole numbers; modern theory allows for larger numbers in organic compounds.
95
What is an alpha particle?
An alpha particle consists of two protons and two neutrons, equivalent to a helium atom that has lost both its electrons.
96
he
97
Nae
98
hà at
99
Whch se-amie pricle w iisovered by
100
A8ATOMSSIRUCTURE
101
eleent hih des ot contanh neuon
102
tais one elcn and one pron will
103
toty y hrge ot
104
he hasis ol Thicn' del of an aom
exain how
105
An atom is buiit up of a number of sub-atomic
106
particles The three sub-atomic particles of great
107
inortance in understandmg the srucure of an atom
108
ane elecsprotons and neutrons
the properties of
109
which ane given in Table 42
110
Table 42 Prperties of sub-atonic particles
111
Parnicle
112
1Blaro
113
2 Proton
114
3 Neutren
115
Sval
116
Hp
117
n
118
Charge
119
There are two structural parts of an atom
the
120
nucleus and the emnpty space in which there are
121
Imagmary paths called orbits.
122
1/1840 91x I0g
123
16x 104g
124
16x 10g
125
mucleus of the atom.
126
iere theoisat
127
baosanicley
128
Orbits (electrons evolve
129
in orbits or shelis)
130
Nuckeus
131
Nucleus
132
called hucleons) are found in the centtal part or
133
(0ontains protors and neutrore)
134
The protons and neutrons lcollectively
135
a) Naie e ells enoed
136
by A Ii and Whih
137
hell bas least ey
138
b) Nante X asd state ihe
139
8) The aove skh is of
140
20 Give the postilates of Išos atoi ok
141
Orbiis They are the imaginary paths whers
142
electrons revolve around the meles of the ato
143
49ATOMIC NUMIBER Z
144
In 1913
Henry Moseley studied how different
145
elements produce different types of X-rays and
146
found that each element has a unique property
147
related to the number of protons in its atom. le
148
discovered that this number
called the atomic
149
number
is what defines an element
150
An atom of an eleent has its own characteristic
151
number of protons in its nucleus
which
152
distinguishes it from the atoms of other elements.
153
This characteristic number (numbher of protons)
154
is called the atomtc nunber of the clement.
155
Atomic number is denoted by Z
156
The atonmic number is
therefore
157
nnber of clectrons in the neutral atom of an
158
element because
159
no. of protons no. of electrons.
160
Number of protons gives the total positive
161
charge present in the nucleus of an atom.
162
Atomic nuber is unique for atoms of each element.
163
The atomic number of an element is the number of :
164
electrons present in its neutral aton.
165
protos present in the nucleus of its atom.
166
positive charge in the nucleus of its atom.
167
he
168
Nae
169
hà at
170
Whch se-amie pricle w iisovered by
171
A8ATOMSSIRUCTURE
172
eleent hih des ot contanh neuon
173
tais one elcn and one pron will
174
toty y hrge ot
175
he hasis ol Thicn' del of an aom
exain how
176
An atom is buiit up of a number of sub-atomic
177
particles The three sub-atomic particles of great
178
inortance in understandmg the srucure of an atom
179
ane elecsprotons and neutrons
the properties of
180
which ane given in Table 42
181
Table 42 Prperties of sub-atonic particles
182
Parnicle
183
1Blaro
184
2 Proton
185
3 Neutren
186
Sval
187
Hp
188
n
189
Charge
190
There are two structural parts of an atom
the
191
nucleus and the emnpty space in which there are
192
Imagmary paths called orbits.
193
1/1840 91x I0g
194
16x 104g
195
16x 10g
196
mucleus of the atom.
197
iere theoisat
198
baosanicley
199
Orbits (electrons evolve
200
in orbits or shelis)
201
Nuckeus
202
Nucleus
203
called hucleons) are found in the centtal part or
204
(0ontains protors and neutrore)
205
The protons and neutrons lcollectively
206
a) Naie e ells enoed
207
by A Ii and Whih
208
hell bas least ey
209
b) Nante X asd state ihe
210
8) The aove skh is of
211
20 Give the postilates of Išos atoi ok
212
Orbiis They are the imaginary paths whers
213
electrons revolve around the meles of the ato
214
49ATOMIC NUMIBER Z
215
In 1913
Henry Moseley studied how different
216
elements produce different types of X-rays and
217
found that each element has a unique property
218
related to the number of protons in its atom. le
219
discovered that this number
called the atomic
220
number
is what defines an element
221
An atom of an eleent has its own characteristic
222
number of protons in its nucleus
which
223
distinguishes it from the atoms of other elements.
224
This characteristic number (numbher of protons)
225
is called the atomtc nunber of the clement.
226
Atomic number is denoted by Z
227
The atonmic number is
therefore
228
nnber of clectrons in the neutral atom of an
229
element because
230
no. of protons no. of electrons.
231
Number of protons gives the total positive
232
charge present in the nucleus of an atom.
233
Atomic nuber is unique for atoms of each element.
234
The atomic number of an element is the number of :
235
electrons present in its neutral aton.
236
protos present in the nucleus of its atom.
237
positive charge in the nucleus of its atom.
238
'p= Z] no. of neutrons n] = A -Z
239
= no. of neutrons [n] + no. of protons Ip
240
1
241
12N
242
12P
243
Mass Number |A)
244
N
245
of magrnesten tom
246
Fig 4h The sarnE
247
2 electrons
248
8 electrons
249
2 electrons
250
No. of neutrons In] =A-Z= I8
251
|A|=n +p= 35
252
Atoic number (Z] =p=e= 17
253
8
254
L M
255
has 19 electrons. Its electronic configuration is
256
For example
potassium (atomic number 9)
257
.. A =n+p
258
So its electronic configuration is 2
8
259
=
260
Mass number |A]
261
=
262
after it has only 8 electrons.
263
18 electrons
yet the fourth shell begins to be filled
264
Although the third shell can accommodate up to
265
elements heavier than argon
the situation changes.
266
electron can occupy an outer shell. However. in
267
18)
each inner shell is completely filled before any
268
In lighter elements
up to argon (atomic number
269
8
270
2
271
N
272
2
273
M shell or III shell =
274
K
275
L shell or II shell
276
K shell or I shell
277
Magnesium has atomic
278
Mass number
279
different shells as follows.
280
electrons that are allotted to
281
neutrons. It is surrounded by 12
282
protons and (24 - 12) = 12
283
Hence its nucleus has 12
284
number 12 and atomic mass 24.
285
8
286
Structure of Magnesium atom
287
đccommnodate a maximum of 2 electrons only
288
which have only one shell
and can thus
289
electrons
except Hydrogen and Helium atom
290
atom can acCOmm0date a maxiImum of &
291
become stable only after acquiring 8 electroms
292
This is due to the fact that the elements
293
4. The outernost shell of a chemically stable
294
in the Outermost shell.
295
18 electrons but only 8 electrons are filled in
296
Atomic Number (Z]
297
The maximun capacity of M shell
298
L M
299
8
300
2
301
.Z=p=e
302
= no. of electrons [el
303
K
304
- 68
305
= no. of protons Ip
306
Atomic number (Z]
307
having 20 electrons is
308
For example
clectronic arrangement in Calci
309
Example :CI
310
Subscript Z = Alomic number
311
Superscript A = Mass number
312
X denotes the symbol of the element
313
X
314
Symbolic representation of Element
315
has the capacity to accommodate more electrons.
316
accommodate more than 8 electrons
even if it
317
3. The outermost shell of an atom cannot
318
the shells are filled in stepwise manner.
319
unless the inner shells are filled. In other words
320
2. Electrons are not accommodated in a given shell
321
and so on.
322
Fourth or N shell has (2 x 42) = 32 electrons
323
Third or M shell has (2 x 32) = 18 electrons
324
Second or L shell has (2 x 22) = 8 electrons
325
First or K shell has (2 x 1) = 2 electrons
326
where n denotes the serial number of that shell.
327
in a particular shell is given by the formula 2n²
328
1. The maximum possible number of electrons
329
or shells.
330
the number of electrons in different energy levels
331
The following rules are followed for writing
332
(orbits) of an atom was suggested by Bohr and Bury.
333
Distribution of electrons into different shells
334
electronic configuration.
335
Distribution of electrons in different shells is called
336
ORBITSBOHR-BURY SCHEME
337
4.10 DISTRIBUTION OF ELECTRONS IN THE
338
sodium is 23 and its atomic mass Is 23u.
339
unit (amu) u. For example
the mass number of
340
units. The atomic mass is expressed in atomic mass
341
is merely a number while atomic mass has specific
342
same as its atomic mass numerically. Mass numnber
343
Note : Mass number of an element is nearly the
344
atomic mass units.
345
approximation of the atomic mass calculated in
346
Mass number
however. is a whole number
347
Mass number is denoted by A.
348
of protons and neutrons present in its nucleus.
349
Mass number of an element is the total number
350
Mass Number (A|
351
'p= Z] no. of neutrons n] = A -Z
352
= no. of neutrons [n] + no. of protons Ip
353
1
354
12N
355
12P
356
Mass Number |A)
357
N
358
of magrnesten tom
359
Fig 4h The sarnE
360
2 electrons
361
8 electrons
362
2 electrons
363
No. of neutrons In] =A-Z= I8
364
|A|=n +p= 35
365
Atoic number (Z] =p=e= 17
366
8
367
L M
368
has 19 electrons. Its electronic configuration is
369
For example
potassium (atomic number 9)
370
.. A =n+p
371
So its electronic configuration is 2
8
372
=
373
Mass number |A]
374
=
375
after it has only 8 electrons.
376
18 electrons
yet the fourth shell begins to be filled
377
Although the third shell can accommodate up to
378
elements heavier than argon
the situation changes.
379
electron can occupy an outer shell. However. in
380
18)
each inner shell is completely filled before any
381
In lighter elements
up to argon (atomic number
382
8
383
2
384
N
385
2
386
M shell or III shell =
387
K
388
L shell or II shell
389
K shell or I shell
390
Magnesium has atomic
391
Mass number
392
different shells as follows.
393
electrons that are allotted to
394
neutrons. It is surrounded by 12
395
protons and (24 - 12) = 12
396
Hence its nucleus has 12
397
number 12 and atomic mass 24.
398
8
399
Structure of Magnesium atom
400
đccommnodate a maximum of 2 electrons only
401
which have only one shell
and can thus
402
electrons
except Hydrogen and Helium atom
403
atom can acCOmm0date a maxiImum of &
404
become stable only after acquiring 8 electroms
405
This is due to the fact that the elements
406
4. The outernost shell of a chemically stable
407
in the Outermost shell.
408
18 electrons but only 8 electrons are filled in
409
Atomic Number (Z]
410
The maximun capacity of M shell
411
L M
412
8
413
2
414
.Z=p=e
415
= no. of electrons [el
416
K
417
- 68
418
= no. of protons Ip
419
Atomic number (Z]
420
having 20 electrons is
421
For example
clectronic arrangement in Calci
422
Example :CI
423
Subscript Z = Alomic number
424
Superscript A = Mass number
425
X denotes the symbol of the element
426
X
427
Symbolic representation of Element
428
has the capacity to accommodate more electrons.
429
accommodate more than 8 electrons
even if it
430
3. The outermost shell of an atom cannot
431
the shells are filled in stepwise manner.
432
unless the inner shells are filled. In other words
433
2. Electrons are not accommodated in a given shell
434
and so on.
435
Fourth or N shell has (2 x 42) = 32 electrons
436
Third or M shell has (2 x 32) = 18 electrons
437
Second or L shell has (2 x 22) = 8 electrons
438
First or K shell has (2 x 1) = 2 electrons
439
where n denotes the serial number of that shell.
440
in a particular shell is given by the formula 2n²
441
1. The maximum possible number of electrons
442
or shells.
443
the number of electrons in different energy levels
444
The following rules are followed for writing
445
(orbits) of an atom was suggested by Bohr and Bury.
446
Distribution of electrons into different shells
447
electronic configuration.
448
Distribution of electrons in different shells is called
449
ORBITSBOHR-BURY SCHEME
450
4.10 DISTRIBUTION OF ELECTRONS IN THE
451
sodium is 23 and its atomic mass Is 23u.
452
unit (amu) u. For example
the mass number of
453
units. The atomic mass is expressed in atomic mass
454
is merely a number while atomic mass has specific
455
same as its atomic mass numerically. Mass numnber
456
Note : Mass number of an element is nearly the
457
atomic mass units.
458
approximation of the atomic mass calculated in
459
Mass number
however. is a whole number
460
Mass number is denoted by A.
461
of protons and neutrons present in its nucleus.
462
Mass number of an element is the total number
463
Mass Number (A|
464
Valercy 2
465
Electronie Cordig 2882
466
20n
467
20p
468
Atom of Calcium Ca
469
Valericy2
470
Electronic Config 285
471
16n
472
16p
473
Atom of Sulphur S
474
Valercy - 2
475
Electronic Corfig 282
476
12n
477
12p
478
Atom of Oygen O
479
Valerey2
480
Fieotrore Crfg
481
Valency=1
482
Electronic Config 2
8
483
p
484
20n
485
19p
486
Atom of Potassium K
487
Valency=3
488
Electronic Config. 2
8
489
16n
490
15p
491
Atom of Sodium Na Atorn of Magnesium Mg
492
Valency 2
493
Valency =3
494
Electroni Gorfig 2zB
495
Atom of Heryitim he
496
Atom of Phosphorus P
497
Valency =1
498
Electronic Config. 2
8
499
12n
500
11p
501
69
502
Electronic Config 2
5
503
7n
504
7p
505
Atom of Nitrogen N
506
Valency1
507
Electronie Gontig 21
508
Jp
509
Atom of Lithium LI
510
Valency=0
511
Electronic Config. 2
8
512
22n
513
18p
514
Atom of Argon Ar
515
Valency = 4
516
Electronic Config. 2
8
517
14n
518
14p
519
Atom of Silicon 20Si
520
Valency= 0
521
Electronic Config. 2
8
522
10n
523
10p
524
Atom of Neon 0Ne
525
Valency = 4
526
Electronic Config. 2.4
527
Atom of Carbon C
528
Valency
529
Electronic Config 2
530
2p
531
Atom of Heliun He
532
Valency 1
533
Electronic Config 2.8
7
534
18n
535
17p
536
Atom of Chlorine cl
537
Valency=3
538
Electronic Config. 28
3
539
14n
540
13p
541
Atom of Aluminium AI
542
Valency =1
543
Electronic Config 2.7
544
10n
545
9p
546
8
547
Atom of Fluorine F
548
Valency=3
549
Electronic Config 2.3
550
Atom of Boron B
551
valency 1
552
Electronc Config1
553
fp
554
Atom of Hydrogen H
555
Valercy 2
556
Electronie Cordig 2882
557
20n
558
20p
559
Atom of Calcium Ca
560
Valericy2
561
Electronic Config 285
562
16n
563
16p
564
Atom of Sulphur S
565
Valercy - 2
566
Electronic Corfig 282
567
12n
568
12p
569
Atom of Oygen O
570
Valerey2
571
Fieotrore Crfg
572
Valency=1
573
Electronic Config 2
8
574
p
575
20n
576
19p
577
Atom of Potassium K
578
Valency=3
579
Electronic Config. 2
8
580
16n
581
15p
582
Atom of Sodium Na Atorn of Magnesium Mg
583
Valency 2
584
Valency =3
585
Electroni Gorfig 2zB
586
Atom of Heryitim he
587
Atom of Phosphorus P
588
Valency =1
589
Electronic Config. 2
8
590
12n
591
11p
592
69
593
Electronic Config 2
5
594
7n
595
7p
596
Atom of Nitrogen N
597
Valency1
598
Electronie Gontig 21
599
Jp
600
Atom of Lithium LI
601
Valency=0
602
Electronic Config. 2
8
603
22n
604
18p
605
Atom of Argon Ar
606
Valency = 4
607
Electronic Config. 2
8
608
14n
609
14p
610
Atom of Silicon 20Si
611
Valency= 0
612
Electronic Config. 2
8
613
10n
614
10p
615
Atom of Neon 0Ne
616
Valency = 4
617
Electronic Config. 2.4
618
Atom of Carbon C
619
Valency
620
Electronic Config 2
621
2p
622
Atom of Heliun He
623
Valency 1
624
Electronic Config 2.8
7
625
18n
626
17p
627
Atom of Chlorine cl
628
Valency=3
629
Electronic Config. 28
3
630
14n
631
13p
632
Atom of Aluminium AI
633
Valency =1
634
Electronic Config 2.7
635
10n
636
9p
637
8
638
Atom of Fluorine F
639
Valency=3
640
Electronic Config 2.3
641
Atom of Boron B
642
valency 1
643
Electronc Config1
644
fp
645
Atom of Hydrogen H
646
() Atoms of all the elements (except hydioge) are mude up o three fndamental (sut
atomiey
647
(iH) The nucleus is positively charged du to the presence of protons in it.
648
i) The ueleus is located at the Centre of the atom It contains protons amd neurons
whih
649
for the lotul maNN of that atom.
650
(iv) The electons are outside the nucleus and have negligible moss.
651
(v) The number of electrons in an atom is equal to the nunber of protons in ib
hence the atom
652
(v) The elecrons revolve rupidly in fived circular paths aound the mucleus
These cirular paths are
653
called energy levels or shells or orbits.
654
(vii) The atoms of dierent elements contain different numbers of electrons
protons and neutrons
655
Flements
656
Helium
657
Hydrogen
658
Lithium
659
Boron
660
Beryllium
661
Carbon
662
Jarticles elecvoIs
protons and neutrons
663
Nitrogen
664
Oxygen
665
Neon
666
Fluorine
667
Sodium
668
electrically neutral.
669
Magnesium
670
Silicon
671
Aluminium
672
Argon
673
Sulphur
674
Phosphorus
675
Chlorine
676
Potassium
677
Calcium
678
Symbol
679
C
680
K
681
Si
682
S
683
Ne
684
Li
685
Na
686
Al
687
Ar
688
Be
689
N
690
He
691
Mg
692
Ca
693
Table 4.3 Arrangement of clectrons in atoms of elements having atomic numbers from I to 20
694
Atomte No
(Z)
695
No of protons/
696
No. of electrons
697
12
698
Main features of the structure of atoms
699
13
700
14
701
15
702
16
703
17
704
18
705
7
706
19
707
20
708
3
709
Mass No. (A)
710
No. of protons No of neutrons Ist or
711
(A-Z) K shell
712
12
713
19
714
20
715
23
716
24
717
27
718
28
719
31
720
32
721
35
37
722
40
723
39
724
40
725
5
726
6
727
7
728
8
729
10
730
10
731
12
732
12
733
14
734
14
735
16
736
16
737
18
20
738
22
739
20
740
20
741
2
742
2
743
2
744
2
745
2
746
2
747
2
748
2
749
2
750
2
751
Distribution of Electrons
752
Znd or Snl or
753
L-shell M-shell
754
2
755
3
756
5
757
6
758
8
759
8
760
8
761
8
762
8
763
8
764
8
765
8
766
8
767
2
768
3
769
4
770
5
771
6
772
7
773
Ath or Valeney
774
N-shell
775
2
776
2
777
2
778
3
779
2
780
1
781
2
782
Metal /
783
non-metall
784
noble gas
785
Non-metal
786
Noble gas
787
Metal
788
Metal
789
Non-metal (solid)
790
Non metal (solid)
791
Non-metal (gas)
792
Non-metal (gas)
793
Non-metal (gas)
794
Noble gas
795
Metal (solid)
796
Metal (solid)
797
Metal (solid)
798
Non-metal (solid)
799
Non-metal (solid)
800
Non-metai (solid)
801
Non-metal (gas)
802
Noble gas
803
Metal (solid)
804
Metal (solid)
