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Na has the highest second ionization enthalpy.

(c) Nitrogen

The electronic configuration of an element determines its position in Modern Periodic table.The element with one valence electron is the first while the element with 8 valence electrons is placed in the 18th group of a period.

The electronic configuration of an element determines its position in Modern Periodic table.

The element with one valence electron is the first while the element with 8 valence electrons is placed in the 18th group of a period.

Atomic radii decrease from left to right across a period. Therefore, first element in a period has highest atomic size.

1. 

2. All these elements we can see one electron in the outermost shell. Hence elements of group I exhibit similarity in chemical properties.

3. Outermost electrons.

4. Same, group number equal tot he number of election in the outermost shell for the elements in groups 1 and 2.

Characteristics which remain similar on moving down a group/ sub-group are: 

1. Valency of electrons. 

2. Chemical properties. 

Characteristics which show a transition or moving down a group are: 

1. Metallic character increases down the group. 

2. Number of electron shells increases down the group. 

3. Atomic size increases down the group. 

4. Ionisation potential decreases down the group. 

5. Electron affinity decreases down the group

(a) Group 1: Lithium< Sodium< Potassium< Rubidium < Caesium< Francium

Group 17: Fluorine < Chlorine < Bromine< Iodine < Astatine

(b) Group 1: Francium

Group 17: Astatine< Iodine< Bromine< Chlorine< Fluorine

(c) Group 1: Francium< Cesium< Rubidium< Potassium< Sodium< Lithium

Group 17: Astatine< Iodine< Bromine< Chlorine< Fluorine

(d) Group 1: Francium

Group 17: Astatine

(e) Group 1: Lithium>Sodium> Potassium> Rubidium> Cesium> Francium

Group 17: Fluorine > Chlorine> Bromine > Iodine > Astatine

These elements belong to Second Period. The missing element is N (Nitrogen) and it should be placed between C and O.

All of them have seven valence electrons.

 The generally is Ionization potential increases from left to right across a period.

The Atomic size is decreases.

All the elements have 2 electrons in their valence shell. 

 In group 2, the atomic size increases down the group. As the atomic size increases, the nuclear charge decreases. Due to this, electrons of the outermost shell lie further away from the nucleus making the removal of electrons easy. So, Ba will form ions readily. 

The ease with which an element loses one or more of its electrons is called its metallic character. On the other hand, the ease with which an element gains one or more electrons is called its non-metallic character. It mainly depends upon atomic size and ionisation potential. More the atomic size and lesser the ionisation potential, more is the metallic character. However, the reverse is true for non-metallic character of an element. In a group atomic size increases while ionisation potential decreases as we move down a group. Thus, down a group metallic character increases while non-metallic character decreases. For example, 

The first five elements of Group 14 are C (At. No. = 6), Si (At. No. = 14), Ge (At. No. = 32), Sn (At. No. = 50) and Pb (At. No. = 68). 

Out of these C (At. No. = 6) is a non-metal, Si (At. No. = 14) and Ge (At. No. = 32) are metalloids while Sn 

(At. No. = 50) —and Pb (At. No. = 68) are metals.

With metals, it will form ionic bond and with non-metal, it will form covalent bond.

1. Nitrogen

2.Li 

3. F.

4. Be

 5. F

Non-metallic character of elements is increases.

1. Group 2, period 4

2. Cl

3. Sodium (Na)

4. Helium (He) 

5. Potassium

1.Si Cl,

2. Strongly basic

1. Element ‘B’ is likely to be more non-metallic in character than element‘A’. 

2. Element ‘Z’ in sub-group 2[IIA] is below element ‘Y’ in the same sub-group. The element ‘Z’ will be expected to have higher atomic size and more metallic character than ‘Y’ 

3. Argon in period 3 is likely to have a larger atomic size than chlorine and its electron affinity value would be zero compared to chlorine. 

4. Across a period- Atomic size and metallic character decreases while I.P., E.A., E.N. and non-metallic character increases and nuclear charge increases. Down a group-Atomic size and metallic character increases while I.P., E.A., E.N. and non- metallic character decreases and nuclear charge increases.

For light elements, Atomic mass = 2 x Atomic number 

In other words, for light elements 

Number of neutrons (n) = Number of protons (p) 

Thus for light elements, nip 1

For example, in 10Ne²⁰ , /? = 10 ; « = 20 -10=10. Thus nip = 10/10=1

For heavier elements, nip > 1. For example, in 17CI³⁷ , p ~ 17 and n = 37- 17 = 20

Thus, nip = 20/17 = 1.176

If nip > 1.5, the nucleus of the elements becomes unstable and the element becomes radioactive. For

example, in radioactive 92U²³⁵ , p = 92 and n = 235 – 92 = 143.

Thus, ntp= 143/92= 1.554. 

(a) Ionisation potential increases across a period left to right. 

Reason: The nuclear charge increases – The nuclear attraction on the outer electrons increases. Hence the outer electrons are more firmly held. 

∴ Ionisation potential increases

(b) Ionisation potential decreased down group. 

Reason: Atomic size increases The nuclear attraction on the outer electrons decreases. Hence the outer electrons are loosely held. 

∴ Ionisation potential decreases.

Density, in general, increases with increase in atomic number. As such density increases as we move down a group from top to bottom. Trend in melting point is different for metals and non-metals as is clear from the change in melting point in Group I or Group 2 (groups which contain only metals), and Group 17 or Group 18 (groups which contain only non-metals). In groups which contain . only metals, m.p. decreases down the group while in groups which contain only non-metals, m.p. increases down the group. Thus in group I, m.p. is in the order ; Li > Na > K > Rb > Cs while in Group 17, m.p. is in the order: F₂>Cl₂<Br₂<I_2.

1. Metals present in period 3 are Na, Mg and Al. 

Non-metals present in period 2 are C, N, O and F.

2. Inert gases i.e. Group 18

3.The non-metal in period 3 having a valency 1.

4.Mg (OH)₂ 

5. HCl

The ionization potential is increases.

Oxidising power means to accept electrons. As we move from left to right along a periodic table, the size of element decrease, hold of nucleus increases, incoming electron is accepted easily thus oxidising power of element increases.

1. Sulphur

2. Cl (Chlorine)

3. ‘Y’ 2, 8,6

4. Ionisation potential

5. Metallic property. 

Reasons for Periodicity in properties in periods and groups. 

1. After definite intervals of atomic number, similar valence shell electronic configuration occurs. 

2. Properties of elements depend upon the number and arrangement of electrons in various shells including valence shells. 

3. In the same period, sub-group, increases or decreases, in a particular property is due to gradual change in electronic configuration in the arranged elements.

Modem periodic table has seven horizontal rows called periods. There is a gradual change in properties with increase in atomic number in the periodic table. 

Across a period, the ionization potential is increases.

Physical and chemical properties of elements are periodic functions of their atomic number. 

Salient Features of Modern Periodic Table – 

1. This table has a eighteen veritcal columns called groups or families. 

2. The groups are IA to VILA, IB to VIIB, VIII (three columns) and zero group. According to the latest recommendations of the International Union of Pure and Applied Chemistry (I.U.P.A.C.), the groups are numbered 1-18. 

3. The group number is assigned to an element depending upon the number of the valence electrons. 

4. Elements included in the same group of the periodic table have similar outer electronic configuration and constitute a family of chemically similar elements.

(a) Periodicity in properties of elements means occurrence of characteristic properties at definite intervals in the modem periodic table, when elements are arranged in increasing order of their atomic number. 

(b) Periodic properties: The properties which appear at regular intervals in the periodic table are called periodic properties. 

Periodic Properties are: 

• Atomic radii Ionisation potential 
• Electron affinity Electro negativity 
• Non Metallic and Metallic character. 
• Density Melting and boiling points. 

(c) Periodicity of elements: Occurrence of elements with similar chemical properties at definite intervals when elements are arranged in increasing order of their atomic numbers is called periodicity of elements.

1. Periods are long [5, 6, 7] horizontal rows of elements in the periodic table and an element with three electron shells and two electrons in its valence shell belongs to period 3 [6, 3, 1] and group 2 [3, 6, 2].

2. Across a period the valence electrons increase by 1 while down a subgroup they remain same.

3. Across a period, the electropositive character decreases and down a group the electronegative character decreases.

4. Elements at the extreme left of the modem periodic table are most reactive, while elements on the extreme right [group 18 (0)] are un reactive.

5. Elements of group 1 [IA] are strong reducing [oxidising / reducing] agents since they are electron donors [acceptors/ donors].

 Down the group, electron affinity decreases.

Noble gas elements have completely filled outer-shell. Such electronic configurations are highly stable and as such noble gases find it difficult to accept electrons. Thus electron affinity of noble gas elements is zero.

This is due to recurrence of similar valence shell electronic configuration after a difference of 2, 8, 18 or 32 in atomic numbers.

1. The element in group 17 [VILA] which is a liquid at room temperature is Br [F, Cl, Br, I],

2. Periodicity in properties is observed in elements after definite intervals due to similar Number of Valence electrons [electronic configuration, number of valence electrons, atomic numbers] of elements.

3. Across a period the nature of oxides and hydrides varies from basic to acidic while the strength of oxy-acids increases from left to right. 

4. Nuclear charge of an atom is the positive charge on the nucleus of an atom, equivalent to the atomic number of an atom.

5. Atomic size of neon is more than the atomic size of fluorine.

Metals are electropositive in nature i.e., they can lose one or more electrons easily. Atoms with large atomic radii and low ionisation potential can easily lose one or more electrons as the nuclear pull on the outer electrons is less. As such, these atoms are more metallic in nature.

(1)

(2)

 The periodic table alkali metals 1.

(1) Trends in periodic properties (Group 1) 

Group 1 elements are Li (At. no. = 3), Na (At. no. = 11), K(At. no. = 19), Rb(At. no. = 37), Cs (At. no. = 55). 

(a) Trend in ionisation potential: On moving down the group, ionisation potential decreases, i. e., ionisation potential decreases in the order: Li > Na > K > Rb > Cs. 

Reason: On moving down the group, atomic size, as well as, nuclear charge increases. However, the effect of increase in atomic size dominates over the effect of increase in nuclear charge. As such ionisation potential decreases down the group.

(b) Trend in electron affinity: On moving down the group, electron affinity decreases, e., electron affinity decreases in the order: Li > Na > K > Rb > Cs. Reason: Same as that in ionisation potential. 

(c) Trend in electronegativity: On moving down the group, electronegativity decreases, e., electronegativity decreases in the order : Li > Na > K > Rb > Cs. Reason: Same as that in ionisation potential. 

(2) Trends in periodic properties (Group 17): Group 17 elements are F (At. no. = 9), Cl (At. no. = 17), Br (At. no. = 35) and I (At. no. = 53). 

(a) Trend in Ionisation potential: On moving down the group ionisation potential decreases, e. ionisation potential decreases in the order : F > Cl > Br > I. 

Reason: On moving down the group, atomic size number of shells as well as nuclear charge increase. However, the effect of increase in atomic size dominates over the effect of increase in nuclear charge. As such ionisation potential decreases down the group. 

(b) Trend in electron affinity: On moving down the group, electron affinity, in general, decreases. However, the actual order of change in electron affinity is : F < Cl > Br > I. 

Reason : Same as in case of ionisation potential. 

(c) Trend in electronegativity: On moving down the group, electronegativity decreases, e., electronegativity decreases in the order: F > Cl > Br > I. 

Reason: Same as in case of ionisation potential.

The three non-metallic elements P, S and Cl are present at the end of period 3 in the modern periodic table. Along a period nuclear charge increases while atomic size decreases. Both of these factors increase the electronegativity. Thus these elements have highest electronegativity.

Except for noble gases, electronegativity increases along a period from left to right and decreases down a group from top to bottom. Therefore, fluorine present at the upper right hand comer of the modem long form of the periodic table has highest electronegativity.

E (Atomic number – 19): 2,8, 8, 1 

F (Atomic number – 8) : 2,6 

G (Atomic number – 17) : 2,8, 7 

E is a metal while F and G are non-metals.

Factors affecting the atomic size are: 

1. Number of shells: As number of shells increases, atomic size i.e. the distance of the outermost shell from the nucleus also increases. 

2. Nuclear charge: As nuclear charge increases, atomic size decreases. This is because a greater nuclear charge means a greater attraction between the nucleus and the electrons in the outermost shell. Lithium(Li) has the largest Atomic size and Fluorine (F) has the smallest Atomic size in period This is because on moving across a period, number of shells remains the same but the nuclear charge increases by one at each step. 

Down a group, nuclear charge as well as number of shells increase. Due to increase in nuclear charge electronegativity should increase. On the other hand, due to increase in number of shells, electronegativity should decrease. However, the effect of increase in number of shells dominates over increase in nuclear charge. As such, on moving down a group, electronegativity decreases.

In group 18 [0 group] inert gases, the outermost shell is completely filled resulting in force of repulsion increasing in atomic radii. 

If there is no change in the number of shells (i.e., in a period), atomic size depends upon nuclear charge. More the nuclear charge, smaller is the atom.

If two combining atoms differ in their electronegativities then the atom with lower electronegativity gives electron (or electrons) while the atom with higher electronegativity accepts these electrons resulting in the formation of ionic bond. On the other hand, if two combining atoms have almost similar electronegativities then such transference of electrons cannot take place. In such a case covalent bond is formed by mutual contribution and mutual sharing of electrons.