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Position of an Element

In a period, the number of valence shell remains the same for all elements. However, the number of electrons in the valence shell increases from left to right.

The position of an element in the periodic table is determined by its electronic configuration e.g. electronic configuration of sodium is 2, 8, 1 i.e., it has three shells and one electron in the outermost shell. Hence, it is placed in period number 3 and group number 1. However, in the case of transition elements this pattern is not followed.

In a group, though the number of shells increases as we move downward, but the number of electrons in the outermost shell remains the same.

In a period, as we move from left to right, the outermost shell or valence shell gets progressively filled from group 1 to group 18 and the shell does not change.

When an atom gain one or more electrons it forms anion. During the formation of anion, the number of orbital electrons become greater than the nuclear charge. Hence, the electrons are not strongly attracted by the lesser number of nuclear charges. Hence anionic radius is higher than the corresponding neutral atom.

• When an neutral atom lose one or more electrons it forms cation,  Na → Na⁺ + e^- 
• The radius of this cation (r_na⁺ )is decreased than its parent atom (r_Na). 
• When an atom is charged to cation, the number of nuclear charge becomes greater than the number of orbital electrons. Hence the remaining electrons are more strongly attracted by the nucleus. Hence the cationic radius is smaller than its corresponding neutral atom.

The term periodicity of properties indicates that the elements with similar properties reappear at certain regular intervals of atomic number in the periodic table.

Example:

• Atomic radii 
• Ionisation energy 
• Electron affinity 
• Electronegativity.

• Some elements in the periodic table show properties that are characteristic of both metals and non-metals. These elements are called semi-metals or metalloids. 
• Example: Silicon. germanium, arsenic, antimony and tellurium.

• In 4f senes, 4f’orbitals arc being progressively filled with electrons, 4f^1-14 5d^0-1 6s² . These elements lie in 6^th period and are called rare earths or lanthanides or lanthanides.
• In 5f series, 5f orbitals are being progressively filled with electrons, 5f¹ 6d^0-1 7s² . These elements lie in 7^th period and are called actinides or actonones.

• The electronic configuration of lanthanides is 4f^1-144 5d^0-1 1 6s² . 
• The electronic configuration of actinides is 5f^1-14 6d^0-1 7s² .

• The elements, whose last electron enters into the f-orbital of the ante-penultimate shell (n-2) are having similar properties are called f-block elements. In these elements (n-2)f orbitals are being filled progressively.
• The two rows of elements placed at the bottom of the periodic table. They are lanthanides and actinides.

d-block elements form a bridge between the chemically active metals of s-block elements and the less active elements of groups of 13^th and 14^th and thus take their familiar name transition elements.

Noble gases are also known as inert gases and do not take part in chemical reactions. They have their outermost shell complete and thus remain stable. They do not generally combine with other substances, nor are they affected by oxidising agents or by reducing agents. They are placed in the 18 or VIIIA group. Since, the outermost shell is complete, the valency is zero, hence VIIIA group is also referred to as zero group.

All the elements belonging to 3 to 12 groups are called transition elements. They resemble each other in several physical and chemical properties. They are all metals. They are called transition elements because they are placed between the most reactive metals on the left and non-metals on the right. Their compounds are coloured. They exhibit variable valency.

In the case of these elements, all shells except the outermost shell are completely filled. Elements belonging to 1 (IA), 2 (IIA), 3 (IIIA), 4 (IVA), 5 (VA), 6 (VIA) and 7 (VIIA) are normal elements. Elements of the second period are known as typical elements [Li (Z = 3) to Ne (Z = 10)] because each element is placed in a group whose number matches with the number of valence electrons. The elements of the IIIrd period are representative elements [Na (Z = 11) to Ar (Z = 18)] as each of them is a representative of its group. Groups 1 (IA) and 2 (IIA) are strongly metallic and are called group of 'alkali metals and alkaline earth metals', while group 7 (VIIA) are halogens.

(b) 7^th period 

In sixth period, 32 elements are present. This period starts with the filling of 6th energy shell, n = 6. There are sixteen orbitais (one 6s, seven 4f, five 4d and three 6p) to be filled. These sixteen orbitais can accommodate 32 (16 × 2 = 32) electrons. 

Hence, 32 elements are present in sixth period.

1. Helium has two electrons. Its electronic configuration is 1s² . As per the configuration, it is supposed to be placed in ‘s’ block, but actually placed in s group which belongs to ‘p’ block. Because it has a completely filled valence shell as the other elements present in 18^th group. It also resembles with 18^th group elements in other properties. 

Hence helium is placed with other noble gases.

2. The other exception is hydrogen. it has only one selectron and hence can be placed in group 1. It can also gain an electron to achieve a noble gas arrangement and hence it can behave as halogens (17^th group elements). Because of these assumptions, position of hydrogen becomes a special case. 

Finally, it is placed separately at the top of the periodic table.

• Metals comprise more than 78% of all known elements. They are present on the left side of the periodic table. 
• They are usually solids at room temperature. [Mercury is an exception (Hg-liquid), gallium (303 K) and cesium (302 K) also have very low melting points]. 
• Metals usually have high melting and boiling points. 
• They are good conductors of heat and electricity. 
• They are malleable and ductile, and also can be flattened into thin sheets by hammering and drawn into thin wires.

• The elements whose last electron enters into the p-orbital of the outermost shell are having similar properties and thus form a group. The ‘np’ orbital of these elements is being progressively tilled. Hence, these elements are named as p-block elements. 
• The groups of 3^th to 18^th in the periodic table belongs to p-block.

1. b. the similarity between the elements to the octaves of music, where every eighth note is comparable to the first.

2. a. 62

3. b. Elements with greater atomic masses

4. b. Because elements that were discovered later could not be ’t into the octave pattern.

5. d. All the options

1. Number of electrons in outermost shell: 

The number of electrons present in the outermost shells does not change on moving down in a group, i.e remains the same.

Hence, the valency also remains same within a group.

2. Number of shells: 

In going down a group the number of shells increases by one at each step and ultimately becomes equal to the period number to which the element belongs. 

3. Valency:

The valencies of all the elements of the same group are the same. The valency of an element with respect to oxygen is same in a group. 

4. Metallic character: 

The metallic character of the elements increases in moving from top to bottom in a group.

Here. x̄ + M₀ = 82 and = 44, s = 12

∴ 44 + M₀ = 82

∴ M₀ = 82 – 44 = 38

Now j = \(\frac{\bar x−M_0}{s}\)

= \(\frac{44−38}{12}=\frac{6}{12}\)

∴ j = 0.5

The correct answer is : (a) 0

Radioactive dust can cause nausea, headache, vomitings, all types of cancers especially skin cancer and leukaemia, white blood cells damage and the damage of brain cells, etc. It can cause vomits and hair fall. The people grow thin and sores appear all over their bodies.

The nuclear reactor should not be installed beside the village at any cost. If it is mandatory, the nuclear reactor must be installed 10 miles away from the habitations and must not be installed near a water body. The authorities concerned should give awareness to nearby residents. The government should minimize the use of nuclear power.

1. She said wistfully that she could remember the time when all the fields around that village were green and the harvests good.

2. It was reported that they had said that the factories needed leather to make shoes, handbags and clothes, their menfolk would get jobs and they would all become rich.

The factories should be built in open non-fertile lands far from habitats. Eco-friendly industries with minimum use of chemicals can be encouraged even in villages or towns.

1. b) with mud walls and a rusting corrugated iron roof

2. b) skull and crossbones symbol

3. b) the drums contained poisonous chemicals.

1. (1) No 

2) any 

3) any 

4) every 

5) All 

6) several 

7) no

8) any

2. (1) Some 

2) every 

3) some 

4) Several 

5) All 

6) all

Adjectives or adjective phrases describing the happy situations in the village : 

picturesque, colourful, noisy, brightest boy, children, and chickens sharing the compound. 

Adjectives or adjective phrases describing the gloomy situations in the village : 

a) rusting corrugated iron roof 

b) frowning 

c) a troubled look 

d) terrible pain 

e) mountain of death in the clearing

i) Some of them are badly corroded, their slimy contents of various colours — grey, dark green, bright orange, etc. – leaking out, down, onto the baked African earth and into the stream. 

ii) Some have fallen down and rolled – or been rolled by playful children – into the bush. 

iii) Some are smoking in the midday heat.

iv) Some are swelling, as if their contents are bursting to get out. 

v) Some have already burst.

They had no money to buy land. So they had no choice.

Yes, Thomas Agonyo was correct because 13 people had died with terrible pain and lots of children were sick because of the metal drums that contained poisonous chemicals.

The slimy contents of various colours are leaking out from the drums and flowing down on to the African earth and into the stream which is a source of drinking water to the villagers. They may cause health hazards.

The people who unloaded drums gave the Chief a brown paper bag which might contain money. So he smiled as the lorries drove away.

Some chemical factories of Italy unloaded metal drums of poisonous chemical near a stream that the villagers get their drinking water from. There were such large empty metal drums outside Mr. Nana’s house. These drums might have fallen down and rolled or been rolled by playful children.

(b) ρ(A) = ρ(A, B) = n

The correct answer is : (c) 0

Vijayasama sighed and reported to the narrator that the leather industry management didn’t tell them that the chemicals would be dumped in open fields and into their rivers. They didn’t tell them that their women would have to walk ten kilometers everyday and they would get ulcer and sores on their bodies.

But the narrator thinks that they don’t know some more hidden hazards till now. They don’t know there won’t be any life in Ponnimanthuri village one day. They will either be died or been forcibly evacuated. By keeping this view the narrator said like that at the end.

Let A = \(\begin{pmatrix} 8 & 9 & 7 \\ 7 & 8 & 6 \\ 9 & 10 & λ \end{pmatrix}\)

Given A is singular matrix ⇒ |A| = 0

\(\begin{vmatrix} 8 & 9 & 7 \\ 7 & 8 & 6 \\ 9 & 10 & λ \end{vmatrix}\) = 0

8 (8λ - 60) - 9(7λ - 54) + 7(70 - 72) = 0

64λ - 480 - 63λ + 486 - 14 = 0

λ + 6 - 14 = 0 ⇒ λ = 8

A = \( \begin{pmatrix} 1 & -3 & 4 & 7 \\ 9 & 1 & 2 & 0\\ \end{pmatrix} \)

Order of A is 2 × 4. So ρ(A) ≤ 2 

Consider the second-order minor

\(\begin{vmatrix}1 & -3 \\9 & 1\end{vmatrix}\)  = 1 + 27 = 28 ≠ 0

There is a minor of order 2 which is not zero. 

So ρ(A) = 2

(b) 1

All the rows except the first row can be made zero

(c) 2

\(\begin{pmatrix} 2 & 0 \\ 0 & 8 \end{pmatrix}\)   \(\begin{vmatrix} 2 & 0 \\ 0 & 8 \end{vmatrix}\)= 16 \(\neq\) 0  

So, p(A) = 2

Given A = \(\begin{bmatrix}4 & 5 & -6 & -1 \\7 & -3 & 0 & 8\\\end{bmatrix}\)

Consider the minor \(\begin{vmatrix}5 & -6 \\-3 & 0\end{vmatrix}\) = -18 \(\ne\) 0

Since a minor of order 2 is not zero, rank is 2

Given A = \(\begin{pmatrix} 1 & 2 & 3 \\ 2 & 3 & 4 \\ 3 & 5 & 7 \end{pmatrix}\)

Consider \(\begin{pmatrix} 1 & 2 & 3 \\ 2 & 3 & 4 \\ 3 & 5 & 7 \end{pmatrix}\)

= 1((21 – 20) – 2(14 – 12) + 3(10 – 9))

= 1 – 4 + 3 

= 0

Since third order minor equals zero, ρ(A) < 3 

Consider = \(\begin{vmatrix} 1 & 2 \\ 2 & 3 \end{vmatrix}\) = 3 – 4 = -1 ≠ 0 

There is a minor of order 2 which is not zero. Hence ρ(A) = 2

Show |A| = 0

(b) -3/2

For A = \(\begin{bmatrix} k & -1 \\ 3 & 2 \end{bmatrix}\) , if |A| = 0, then inverse does not exists \(\begin{vmatrix} k & -1 \\ 3 & 2 \end{vmatrix}\) = 0 gives 2k + 3 = 0 gives 2k + 3 = 0 or k = -3/2

(C) Democracy

Anyone who opposed the government could be jailed without much delay and kept imprisoned for a long time without going to court. Freedom of speech was also curtailed.

Qualities of Mahatma Gandhi: 

1. Truthful, 
2.  Non-violence, 
3.  Simplicity.