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When elements are arranged in the ascending order of their atomic weights, every eighth element starting from a given element resembles in its properties to that of starting element. This is called Newlands’ law of octaves.

Vertical columns of the periodic table are known as groups.

(i) The number of valence electrons remains constant when we move down the group.

(ii) The number of occupied shells increases down the group.

(iii) The size of the atom increases down the group.

(iv) The metallic character of elements increases down the group.

(v) The effective nuclear charge decreases down the group.

The shape of muscles depends on the ability to adapt to external forces. When placed under high demand, they generate great strength and power and maintain durability. Muscle is a soft tissue and their cells contain protein, filaments of actin and myosin that slide past one another, producing a contraction that changes both the length and shape of the cell.

In order to cause the movement of muscles, muscles change their shapes and arrangement in cell in response to nervous impulse. The new arrangement of proteins thereby, give the muscle cells a shorter form and move in direction according to the mind.

The two main organs of CNS are brain and spinal cord. 

Spinal cord plays a major role in sending command to muscles to act without involving thinking process. This phenomenon is called reflex action.

Hormones are the chemical substances which co-ordinate and control the activities of living organisms and also their growth.

Gallium and Scandium.

Correct option is  B) Co, Ni

• Nonmetals present in group 17 (halogen family) and group 16 (chalcogens) have highly negative electron gain enthalpies.
• As a result, they readily accept one or two electrons and form anions (X^– or X^2–) that have complete octet.
• Therefore, nonmetals present in group 17 and 16 are highly reactive.

1. b. Cobalt

2. c. Nickel

3. c. 27

4. a. 28

5. a. 1

True

Newlands adjusted three elements in the same slot

Z = 101 IUPAC name : Mendelevium 

Z = 102 IUPAC name : Nobelium 

Z = 109 IUPAC name : Meitnerium 

Z = 110 IUPAC name : Darmstadtium

Elements are classified for systematic and simplified study of elements and their compounds. The basic property of elements used in the Modern Periodic Table is the atomic number of the elements. Modern Periodic Law states that "the properties of elements are a periodic function of their atomicnumber."
Metals are found on the left side and centre of the Modern PeriodicTable.
Non-metals are found on the right side of the Modern Periodic Table.
Metalloids are found in a zig-zag manner between the metals and the non-metals.

Correct option is: (C) Valency electrons

In a group, each elements have same number of valence electrons, but they have different number of shells.

(C) Valency electrons

True

a periodic recurrence of elements with similar physical and chemical properties.

(a) A-2, B-3, C-4, D-1

(b) A-3, B-1, C-4, D-2

Correct option is : (D) proton number

The serial number of an element in Mendeleev's periodic table was recognized as proton number.

(D) proton number

(i) Aim of classification: Systematic Study of the known elements.

(ii) Basic property: Atomic number. 

(iii) Properties of the elements are a periodic function of their atomic numbers.

(iv) Metals on the left.

(v) Non-metals on the right.

(vi) Metalloids at the border of metals and beginning of non-metals.

Correct option is : (C) Chlorine

In general the electron gain enthalpy (magnitude) increases along a period as we move from left to right and decreases as we move down in a group, but due to small size of 'F' it has less electron gain enthalpy than Cl

Hence, Cl has highest negative electron gain enthalpy

Correct option is (C) Chlorine

True

Electronic configuration of hydrogen resembles that of alkaline earth metals

1. a. number of protons in the nucleus of an atom.

2. c. Elements arranged on the basis of increasing atomic number

3. d. 4

4. b. 18

5. b. 7

(a) The p H scale ranges from 0 to 14.

p H = 7 , Solution is neutral

p H <7 , Solution is acidic

p H >7 , Solution is basic

(b) One advantage of measuring the pH of unknown solution by using pH paper is that we can come to know whether the solution is acidic, basic or neutral without wasting the solution.

False 

It was Henry Moseley who proposed that the atomic number of an element is a more fundamental property than its atomic mass.

Correct option is: (A) atomic number

According to Moseley, the fundamental properties of an element is periodic function of their atomic number.

(A) atomic number

Moseley only proposed atomic number of an element is a more fundamental property than it’s atomic mass by doing this prediction of properties of elements could be done with more precision.

In Newland’s Octaves, the properties of lithium and sodium were found to be the same. This arrangement is also found in Dobereiner triads.

In this system, elements that differed from each other in atomic weight by 16 or multiples of 16 fell very nearly on the same vertical line. Elements lying directly under each other showed a definite similarity. This was the first periodic law

(a)Yes,Dobereiners triads also exist in the columns of Newlands’ Octaves. Consider the elements lithium (Li), sodium (Na) and potassiu m (K) which are present in the second column of Newlands’ classification of elements. Now, if we start with lithium as the 1 st element, then the 8 th element from it is sodium, and according to Newlands’ law of octaves, the properties of 8 th element , sodium should be similar to thos e of the 1 st element, lithium. Again, if we take sodium as the 1 st el ement , then the 8 th element from it is potassium, and according to Newlands ‘ law of octaves, the properties of 8 th element, potassium should be similar to those of the 1 st element, sodium. This means that according to Newlands’ law of octaves, the elements lithium, sodium and potassium should have similar chemical properties. We also know that lithium, sodium and potassium form a Dobereiner’s triad having similar chemical properties. From this, we conclude that Dobereiners triads also exist in the columns of Newlands Octaves.

(b) The main limitation of Dobereiner’s classification of elements was that it failed to arrange all the then known elements in the form of triads of elements having similar chemical properties. Dobereiner could identify only three triads from the elements known at that time. So, his classification of elements was not much successful. Another limitation was that Dobereiner failed to explain the relation between atomic masses of elements and their chemical properties.

(c) Newlands’ law of octaves for the classification of elements had the following limitations:

( i ) Newlands’ law of octaves was applicable to the classification of elements up to calcium only. After calcium, every eighth element did not possess the properties similar to that of the first element. Thus, this law worked well with lighter elements only.

(ii) Newlands assumed that only 56 elements existed in nature and no more elements would be discovered in the future. But later on, several new elements were discovered whose properties did not fit into Newlands’ law of octaves.

(iii) In order to fit elements into his table, Newlands put even two elements together in one slot and that too in the column of unlike elements having very different properties. For example, the two elements cobalt (Co) and nickel (Ni) were put together in just one slot and that too in the column of elements like fluorine, chlorine and bromine which have very different properties from these elements.

(a) Newlands.

(b) Dobereiner.

The 1^st ionization enthalpy of magnesium is higher than that of Na due to higher nuclear charge and slightly smaller atomic radius of Mg than Na. After the loss of first electron, Na⁺ formed has the electronic configuration of neon (2,8). The higher stability of the completely filled noble gas configuration leads to very high second ionization enthalpy for sodium. On the ther hand, Mg⁺ formed after losing first electron still has one more electron in its outermost (3 s) orbital. As a result, the second ionization enthalpy of magnesium is much smaller than that of sodium.

(a) A-4, B-3, C-1, D-2

(1) Dobereiner – Triads 

(2) Newlands – Octaves 

(3) Moseley – Atomic number 

(4) Mendeleev – Atomic mass.

• The long form of periodic table of the elements is constructed on the basis of modem periodic law. The arrangement resulted in repeating electronic configurations of atoms at regular intervals. 
• The elements placed in horizontal rows are called periods and in vertical columns are called groups. 
• According to IUPAC, the groups are numbered from I to 18. 
• There are 18 vertical columns which constitute 18 groups or families. All the members of a particular group have similar outer shell electronic configuration.
• There are 7 horizontal rows called periods.

The elements are shown in the above table along with its atomic numbe. 

• The atomic number also indicates the number of electrons in the atoms of an element. 
• This periodic table is important and useful because we can predict the properties of any element using periodic trend, even though that element may be unfamiliar to us.

1. The effective nuclear charge of magnesium is higher than that of sodium. For these reasons, the energy required to remove an electron from magnesium is more than the energy required in sodium. 

Hence, the first ionization enthalpy of sodium is lower than that of magnesium. 

2. Noble gases have completely filled electronic configuration and they are more stable. So in Noble gases addition of electron is not possible. Electron gain enthalpy is always the amount of energy released (-ve sign) when an electron is added to an atom. – Butin noble gases, if an electron is added, they have positive value of electron gain enthalpy.

Merits of Moseley’s long form of periodic table:

• As this classification is based on atomic number, it relates the position of an element to its electronic configuration. 
• The elements having similar electronic configuration fall in a group. They also have similar physical and chemical properties. 
• The completion of each period is more logical. In a period as the atomic number increases, the energy shells are gradually filled up until an inert gas configuration is reached. 
• The position of zero group is also justified in the table as group 18.
•  The table completely separates metals and nonmetals. 
• The table separates two sub groups. lanthanides and actinides, dissimilar elements do not fall together.
• The greatest advantage of this periodic table is that this can be divided into four blocks namely s, p. d and f-block elements. 
• This arrangement of elements is easier to remember, understand and reproduce.

1. False – Moseley’s periodic table is based on atomic number. 

2. True 

3. True 

4. False – Aluminium wires are used as electric cables because it is a good conductor of heat and electricity. 

5. False – An alloy is an homogeneous mixture of metals.

The English scientist Henry Moseley demonstrated, with the help of the experiments done using X-ray tube, that the atomic number (Z) of an element corresponds to the positive charge on the nucleus or the number of the protons in the nucleus of the atom or that element. He suggested that ‘atomic number’ is more. fundamental property of an element rather than its atomic mass. On the basis of this research, elements were arranged in the order of their increasing atomic numbers in a more systematic way. Accordingly, the statement of the modern periodic law was stated.

• The number of electrons increases by the same number as the increase in the atomic number. 
• As the number of electrons increases, the electronic structure of the atom changes. 
• Electrons in the out cannost shell of an atom (valence shell electrons) determine the chemical properties of the elements.

• Henry Moseley studied the X-ray spectra of several elements and determined their atomic numbers (Z). 
• He discovered a correlation between atomic number and the frequency of X-rays generated by bombarding an clement with high energy of electrons.
• Moseley correlated the frequency of the X-ray emitted by an equation as, 

√v = a (Z – b) 

Where υ = Frequency of the X-rays emitted by the elements. 

a and b = Constants. 

• From the square root of the measured frequency of the X-rays emitted, he determined the atomic number of the element.

Variation in period: 

The number of valence electrons increases from I to 8 on moving across a period. The valency of the elements with respect to hydrogen and chlorine increases from 1 to 4 and then decreases from 4 to zero. 

Variation in group: 

On moving down a group, the number of valence electrons remains same. All the elements in a group exhibit same valency. 

For example, all the elements of group I have valency equal to 1. 

Hence, valency is a periodic property.

(d) Oxidation number

(c) Atomic radius

• The size of an atom is very small (∼ 1.2Å i.e 1.2 × 10¹⁰ ) 
• The atom is not a rigid sphere; it is more like a spherical cotton ball rather than like a cricket ball. 
• It is not possible to isolate an atom and measure its radius. 
• The size of an atom depends upon the type of atoms in its neighborhood and also the nature of bonding between them.

Atomic radius is the distance between the center of its nucleus and the outermost shell containing the electron.

Atomic radius is a periodic property. 

1. Variation in periods: 

The atomic radius decreases while going from left to right in a period. As we move from left to right in a period, the nuclear charge increases by one unit in each succeeding element. But the number of the shell remains same. Hence, the electrons are attracted strongly by the nucleus. Hence the atomic radius decreases along the period. In 2^nd period.

r_Li >r_Be>r_B >r_C >r_N >r_O >r_F

2. Variation in a group: 

The atomic radius of elements increases with increase in atomic number as we move from top to bottom in a group. The attraction of the nucleus for the electrons decreases as shell number increases. Hence atomic radius increases along the group. In 1 group r_Li < r_Na < r_K < r_Rb < r_Cs

Hence, atomic radii is a periodic property.

1. Size of the atom: 

If the size of an atom is larger, the outermost electron hell from the nucleus is also larger and hence the outermost electrons experience lesser force of attraction. Hence it would be more easy to remove an electron from the outermost shell. Thus, ionization energy decreases with increasing atomic sizes.

Ionization enthalpy ∝ \(\frac{1}{Atomic \, size}\)

2. Magnitude of nuclear charge: 

As the nuclear charge increases, the force of attraction between the nucleus and valence electrons also increases. So, more energy is required to remove a valence electron. Hence I.E increases with increase in nuclear charge. 

Ionization enthalpy α nuclear charge

3. Screening or shielding effect of the inner electrons: 

The electrons of inner shells form a cloud of negative charge and this shields the outer electron from the nucleus. This screen reduces the coulombic attraction between the positive nucleus and the negative outer electrons. 1f screening effect increases, ionization energy decreases.

 Ionization enthalpy ∝ \(\frac{1}{Screening \, effects}\)

4. Penetrating power of sub shells s, p, d and f: 

The s-orbital penetrate more closely to the nucleus as compared to p-orbitais. Thus, electrons in s-orbitals are more tightly held by the nucleus than electrons in p-orbitais. Due to this, more energy is required to remove a electron from an s-orbital as compared to a p-orbital. For the same value of ‘n’ , the penetration power decreases in a given shell in the order. s > p > d > f.

5. Electronic configuration:

If the atoms of elements have either completely filled or exactly half filled electronic configuration, then the ionization energy increases.

The energy required to remove the most loosely held electron from an isolated gaseous atom is called as ionization energy.

(d) (i), (ii) and (iii)

Answer: (a) Zr, HF