Unit 1: Periodic Table and Periodic Properties — Short Questions

The amount of energy which is required to remove one valance electron from one mole of isolated gaseous atoms to form mono-positive gaseous ions is called 1st ionization energy.
Example:
Na(g) ——>e⁻ + Na(g)⁺ ΔH₁₁ = +496 kJ/mol

Sulfur has four electrons in its 3p sub-shell while phosphorous has three electrons in its 3p sub-shell which makes phosphorous more stable than sulfur due to half filled stability rule, as shown in given example.
¹⁵P=[Ne] 3s² 3p¹ₓ 3p¹ᵧ 3p¹ᵤ
¹⁶S=[Ne] 3s² 3p²ₓ 3p¹ᵧ 3p¹ᵤ

So, it is easy to remove one electron from sulfur but difficult to ionize phosphorous.

The elements in group 13 to 17 are called p-block elements because their valence electrons are ended up in p-sub shell. According to valance electrons the elements are classified as s, p, d and f-block elements.

Factors affecting the electronegativity are:
(i) Atomic size: Greater the atomic size, lesser will be the electronegativity.
E.N ∝ 1/Atomic Size
(ii) Effective nuclear charge (Z-effect) Greater the value of effective nuclear charge, larger will be the electronegativity.
E.N ∝ Effective nuclear charge

The main factors which are responsible for increasing the reactivity of alkali metals are "increase in atomic size" and "low ionization energy" down the group. As we know alkali metals have only one valence electron in their shells, a low ionization energy is required to remove valence electron and hence their reactivity increases. Increase in atomic size down the group also makes them reactive.

Some of the elements can show variable oxidation numbers because they can expand their octet by exciting their electrons to the empty orbitals if they have. If the elements do not have empty orbitals, then they cannot show variable oxidation number. Examples: Oxidation number of P is +3 in PCl₃ and +5 in PCl₅, while Na, Mg, Ca cannot show variable oxidation states.

X is the element present in 5ᵗʰ period. So, its valence shell configuration ended up in 5ᵗʰ shell having principal quantum number 5. And its electron is showing its group number "15".
X = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 3d¹⁰ 4p³ 5s² 5p³
n = 5, 5s² 5p³
5ᵗʰ period 15ᵗʰ group 5s² 4d¹⁰ 5p³
2 + 10 + 3 = 15
X = Sb=5]

Na and Mg are present at the left side of the periodic table and they are metals as well. So, that's why their oxides are more ionic in nature. While moving to the right side of the periodic table ionic character is decreased and the elements are non-metals as well. So, their ionic character decreased like in nitrogen and phosphorous oxides.

Both Na and Mg can react with oxygen. Na gives golden yellow flame and forms peroxide while in limiting amount of oxygen Na can form normal oxide.
2Na(s) + O₂(g) ——> Na₂O₂(s) (white solid)
(excess) (peroxide)
4Na(s) + O₂(g) ——> 2Na₂O(s) (white solid)
(limited) (normal oxide)
Mg gives intense white flame with oxygen
2Mg(s) + O₂(g) ——> 2MgO (white solid)
(normal oxide)
Both Na and Mg give chlorides with chlorine.
2Na(s) + Cl₂(g) ——> 2NaCl(s) (white solid)
Mg(s) + Cl₂(g) ——> MgCl₂(s)
(white to colourless solid)

Lithium is metal and has the tendency to lose electron easily. While helium is a noble gas and has filled valance shell, so its ionization energy is very high as compared to lithium despite the fact that helium has +2 charge while lithium has +3 nuclear charge.

The reason is lies in the stability of electronic configuration of Be which has filled 2s sub-shell unstable configuration of B which has one electron in its 2p sub-shell.
₄Be = 1s² 2s²
₅B = 1s² 2s² 2p¹

The common thing in Na⁺, Mg²⁺, Al³⁺, Ne⁰, and F⁻ is that all these are iso-electronic species and have 10 electrons in them. Their increasing sizes order is
Al³⁺<Mg²⁺<Na⁺<Ne<F⁻

Neutral chlorides These chlorides in which chloride ion and metal ions are surrounded by water (hydrates) are called neutral chlorides. In these chlorides, they simply ionizes and do not react with water. Their pH near to 7.
NaCl(s) ——> Na⁺(aq) + Cl⁻(aq) (pH = 7)
MgCl₂(s) ——> Mg²⁺(aq) + 2Cl⁻(aq) (pH = 6.5)
Acidic chlorides
These chlorides which can react with water and produced H⁺ ion to give acidic solutions. Chlorides of Al to S from IIIA to VIA give acidic chlorides. This process is called hydrolysis.
PCl₅(s) + 4H₂O(l) ——> H₃PO₄ + 5HCl(aq) (pH = 0)

By 1700 A.D., only 12 elements were recognized Gold (Au). Silver (Ag), Copper (Cu), Iron (Fe), Lead(Pb), Tin(Sn), Mercury (Hg), Phosphorous (P), Sulfur (S), Carbon (C), Zinc (Zn) and Arsenic (As).

In 1829, Dobereiner grouped three elements in such a way that the atomic mass of the middle element is the average of atomic masses of first and third elements. In this way he noticed some periodicity in the elements.
Example
⁷Li, ²³Na, ³⁹K
Na = (7 + 39)/2 = 23

After every eight elements the next element show periodicity with first element if they are arranged on the basis of their atomic masses. It is called Newland's Octaves.

In 1869 Dimitri Mendeleev stated his periodic law, it is stated as: Properties of the elements are the periodic functions of their atomic masses.

In 1869, Lother Meyer developed the famous curves between atomic weight and atomic volume of the elements, These curves also showed periodicity.

Properties of the elements are the periodic functions of their atomic numbers. This Moseley's law also called modern periodic law.

There are 7 periods and 18 groups, vertical columns are groups while periods are horizontal row. 18 groups are further divided into 8-A and 10-B groups.

Elements which have the tendency to lose electron easily are called metals.
e.g: Li, K, Cs etc
Elements which have the tendency to accept electrons easily are called non-metals. e.g: N, O, F etc.

Elements which have the properties some of the metals and some of the non metals are called metalloids. They are also referred as semi metals. Position: They are present in the P-block in "Stair-step line" arrangement including B from IIIA and to the Po of VIA.

Elements can be classified as s, p, d and f-block elements, because of their valence electrons are ended up in respective sub shell. If the valence electron are ended up in s-sub shell, then they are called s-block elements. And if their valence electrons are present in p-sub shell then they are called p-block elements.

The series of 14 elements after the element Lanthanum -57 are called Lanthanides and the 14 elements after the element Actinium -89 are called Actinides. Both these series are also called f-block elements.

Some of the families in the periodic table are:

• Alkali metals (Li, Na, K, Rb, Cs, Fr)
• Alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra)
• Transition metals (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn)
• Chalcogens (O, S, Se, Te, Po, Lv)
• Halogens (F, Cl, Br, I, At, Ts)
• Noble gases (He, Ne, Ar, Kr, Xe, Rn, Og)

Chalogens word derived from two Greek words "Chalcos" means "copper" and "gen" means "form". So, group 16 elements are called Chalcogens are also called copper giver. Elements of this group are O, S, Se, Te, Po, Lv.

The word "halogen" means "salt-former" because these elements easily react with alkali metals and alkaline earth metals to form stable halide salts. Elements include in this group are F, Cl, Br, I, At, Ts.

Due to their stable electronic configuration (complete outer most shell), they are almost entirely unreactive under normal conditions and rarely form compounds. Elements in this group are He, Ne, Ar, Kr, Xe, Rn, Og.

Cations When an atom carries positive charge, it forms cation.
It forms by losing electron.
It's size is smaller than its parental size. eg: Li⁺, Na⁺

Anions When an atom carries negative charge, it forms anion.
It forms by accepting electron.
It's size is greater than its parental size. eg: F⁻, Cl⁻

Elements diagonally positioned in the periodic table show some similarities in "diagonal relationship" despite the fact that they are present in different groups. For example lithium and magnesium, sodium and calcium have some common physical and chemical properties like sizes of their atoms and ions, charge densities, polarizing powers etc.

It is the amount of energy which is required to remove an electron from outermost shell of an isolated gaseous atom to form positive ion.
Na(g) ——> Na⁺(g) + e⁻ ΔH₁₁ = +496 kJ/mol

Those electrons which are present in same orbital experience some repulsion. It is easy to remove electron that is present in the paired form as compared to those electrons which are present in unpaired form due to spinning of electrons. It is called "Spin-paired repulsion".

He has 4 electrons as 1s², 2s² which makes it stable configuration of filled s-sub shell. He has five electron as 1s² 2s² 2p¹ and it's configuration shows that it is relatively unstable due to one electron in its p-sub shell. That's why its value is 801kJ/mol while that of Be is 899kJ/mol even that it has smaller size than Be.

Electron affinity value increases in a period as we move from left to right, because of smaller size and increase in effective nuclear charge (z-effect or proton effect).

It is the power of an atom to attract the shared pair of electrons towards itself in a molecule trend of electronegativity in the 2ⁿᵈ period is increased from left to right.
2ⁿᵈ Period | Li | Be | B | C | N | O | F
E.N | 1 | 1.5 | 2 | 2.5 | 3 | 3.5 | 4

Metallic character of an element is the tendency to lose electron. It increases down the group and decreases in a period.

Sodium can react with O₂ vigorously in air to give peroxide while in limited amount of oxygen it forms normal oxide.
2Na + O₂ ——> Na₂O₂ (Peroxide)
4Na + O₂ ——> 2Na₂O (Normal oxide)

Non metallic oxides are acidic in nature because when they react with water, they form acids.
CO₂ + H₂O ——> H₂CO₃

Metallic oxides are basic in nature because when they react with water, they form base.
Na₂O + H₂O ——> 2NaOH

These oxides which act as an acid and as well as a base are called amphoteric oxides.
Example: ZnO, Al₂O₃ and BeO
Al₂O₃ + 6HCl ——> 2AlCl₃ + 3H₂O
Al₂O₃ + 2NaOH ——> 2NaAlO₂ + H₂O

P₄O₆ 4(O.N of P) + 6(O.N of O) = 0
4(O.N of P) + 6(-2) = 0
4(O.N of P) - 12 = 0
4(O.N of P) = 12
P = 12/4 = +3

P₄O₁₀ 4(O.N of P) + 10(O.N of O) = 0
4(O.N of P) + 10(-2) = 0
4(O.N of P) - 20 = 0
4 P - 20 = 0
P = 20/4
P = +5

See Q11. of theory.

See Q12. and Q13. of theory.

See Q8. of theory.

See Q7. of theory.