Periodic Table of Elements

Periodic table elements are arranged according to the modern law of the periodic table in chemistry in order of increasing atomic number or the full number of protons in the atomic nucleus. According to the modern law or long form of the periodic table, the list of chemical elements along groups and periods is organized on the basis of electronic configuration and classified into four categories s, p, d, and f-block elements. The modern law for the periodic table of elements suggests that the physical and chemical properties of elements are the periodic functions of the atomic number. The modern law of the periodic table comes due to the breakdown of Mendeleev’s (1861) scientific classification based on atomic weight or masses of the chemical elements. The names, symbols, atomic numbers, and electronic configuration of 118 periodic table elements are given below in the picture:

Modern Periodic Table

The modern law for the periodic table of elements comes because it helps to remove the defects of Mendeleev’s scientific classification. According to the modern periodic table chart in chemistry or chemical science, the elements are represented by two parts, vertical columns (groups) and horizontal rows (periods).

The initial discovery was explained by Dmitri Ivanovich Mendeleev in 1861 and Mosely in 1911. However, the Bohr model suggested the scientific development of groups and periods of the 118 periodic table elements.

Periods in Periodic Table of Elements

The periods on the periodic table contain horizontal rows for the arrangement of chemical elements. Thus, the long form or modern form of the periodic table contains seven (7) periods for the accommodation of elements.

First Period

The principal quantum number (n) = 1 for the first period of the periodic table. It indicates that there is only one main energy level for this period. Therefore, this period has two chemical elements beginning with hydrogen and ending with inert gas helium.

Second Period

The second period has two sub-shells (2s and 2p) in which chemical elements are arranged. Therefore, this period contains (2 + 6) = 8 chemical elements. It begins with the alkali metal lithium and ends with the inert gas neon.

Third Period

Similarly, the third period has two sub-shells (3s and 3p) for the arrangement of chemical elements. Therefore, this period also contains (2 + 8) = 8 chemical elements. It begins with the alkali metal sodium and ends with the inert gas argon.

Fourth Period

There are three sub-shells (4s, 4p, and 3d) in the third period of the periodic table. Therefore, this period contains (2 + 6 + 10) = 18 chemical elements. It begins with an alkali metal potassium and ends with an inert gas krypton.

Fifth Period

Similarly, there are three sub-shells (5s, 5p, and 4d) for the elements in this period. Therefore, this period also contains (2 + 6 + 10) = 18 chemical elements.

Fifth period begins with the alkali metal rubidium and ends with the inert gas xenon. It contains eight typical elements and ten transition metals.

Sixth Period

The sixth period has four sub-shells (6s, 6p, 5d, and 4f) for the periodic arrangement of chemical elements. Therefore, this period contains (2 + 6 + 10 + 14) = 32 chemical elements. It begins with the alkali metal cesium and ends with the inert gas radon.

The sixth period contains eight typical elements, ten transition metals, and fourteen lanthanides or rare earth elements. The lanthanides (lanthanum to ytterbium) are placed in the lower position of the periodic table.

Seventh Period

The seventh period has four sub-shells (7s, 7p, 6d, and 5f) for the periodic arrangement of chemical elements. Therefore, this period also contains (2 + 6 + 10 + 14) = 32 chemical elements. It begins with the radioactive francium and ends with oganesson.

Most of the elements in this period are highly radioactive and man-made elements. The actinides (actinium to nobelium) are also placed in the lower position of the periodic table.

Groups in Periodic Table of Elements

Groups in the periodic table are the vertical columns in which chemical elements are arranged. The modern or long form of the periodic table contains eighteen (18) groups during the arrangement of 118 chemical elements.

• Groups 1 and 2, and groups 13 to 17, contain the typical chemical elements of the period table. Therefore, all the elements in a particular group consist of the same number of valence shell electrons in their outer quantum shell.
• Group 3 to Group 12 elements are generally called transition metals or d-block elements.
• Group 18 contains inert or noble gases starting with helium and ending with oganesson.

In the modern periodic table, the elements on the left side are metals while those on the right side are nonmetals. The transition elements are also placed between the metals and nonmetals of the periodic table.

Periodic Table of Elements List

The list of chemical elements arranged in groups and periods of the periodic table is listed below in the table.

Long Form of Periodic Table

According to the above definition and explanation, the long form of the periodic table elements has three units: left, right, and middle sections for learning chemistry or chemical science.

Left Portion

The left section or portion of the table contains Group 1 (alkali metals) and Group 2 (alkaline earth metals).

These elements have extremely high electropositive character and very low ionization energy. Therefore, all these elements always show a positive oxidation number or state.

Right Portion

The right portion contains Group 13 to Group 18 elements. This portion of the table contains metals, metalloids, non-metals, and noble gases.

Most of the nonmetals have high electron affinity. However, noble gases (helium, neon, argon, krypton, xenon, and radon) are non-reactive in nature.

Middle Portion

The organization of the middle portion (group 3 to group 12) of the periodic table elements mostly establishes the relationship between the left and right sections. Therefore, the middle portion contains a list of transition metals or d-block and inner transition or f-block elements.

Blocks of Periodic Table Elements

The modern periodic law is based on the atomic number and valence shell electron arrangement of atoms. According to the valence shell electron arrangement of elements, the different types of metals and non-metals are arranged to form the s, p, d, and f-blocks of the periodic table.

s-Block Elements

The names of s-block elements in the periodic table are given according to the arrangement of electrons. Therefore, in the s-block, the valence electron enters the ns-orbital. They are filled progressively according to the electron configuration rules.

Group-1 (hydrogen, lithium, sodium, potassium, rubidium, cesium, and francium) and also group-2 (beryllium, magnesium, calcium, strontium, barium, and radium) belong to the s-block elements.

The valence shell electron configuration of s-block elements = ns^1→2. Here, n = principal quantum number, or the number of periods.

p-Block Elements

Similarly, p-block elements on the periodic table are organized by progressively filled p-orbital in valence shell electronic structure. However, helium is an exception with electron arrangement 1s².

Groups 13 to 17 and noble gases (group 18) belong to the p-block elements in the periodic table. The second period of p-block elements (boron, carbon, nitrogen, oxygen, fluorine, and argon) also contains filled s-orbitals.

Therefore, the valence shell electron configuration of such elements = 2s² 2p^1→6, where n = number of periods.

d-Block and f-Block Elements

The name d-block (transition) or f-block (inner transition series) elements on the periodic table is given due to the presence of progressively filled d or f-orbitals in the valence shell electronic structure.

The transition or inner transition family generally forms an ionic chemical bond with metals (s-block). Similarly, a covalent bond forms with non-metals (p-block).

3d-block elements (scandium, titanium, vanadium, chromium, iron, cobalt, nickel, copper, and zinc) are placed in the middle of the table. Therefore, they occupy between s and p-block with valence shell electronic configuration, 4s^0→2 3d^1-10.

The f-block elements on the periodic table are divided into two series, 4f or lanthanides and 5f or actinides. The f-block also contains many missing elements discovered or synthesized by the nuclear reaction of radioactive isotopes.

Periodic Table Trends of Elements

Understanding the periodic table variation of ionization energy, electron affinity, electronegativity, acid-base properties, oxidation number, and redox reaction of chemical elements is the most important characteristic for any discussion or information in chemistry or science.

In learning chemistry, we generally summarize various physical and chemical properties within the group and period.

Atomic Radii

The term atomic radii generally uses to derive the distance between the nucleus and the outermost shell of electrons.

When moving left to right in a period, the atomic radii of elements decrease because the number of protons or nuclear charge in the atom increses. However, the outermost electronic shell remains unchanged but the nuclear charge in the same outermost electronic shell increses. Therefore, the outer electrons are attached more strongly to the nucleus.

When we go down in a group, the atomic radii of elements increses due to the addition of new electrons to higher energy levels. It also decreases the electrostatic attraction between the nucleus and valence shell electrons.

Ionization Energy of Periodic Table Elements

Ionization energy (I or IE) defines the amount of energy required when we want to remove the most loosely bound electron from an isolated gaseous atom of an element in its lowest energy state or ground state to produce a cation.

M (g) + Ionization energy → M⁺ + e⁻

The value of ionization energy generally increses in moving from left to right in a period. When we move from left to right in a period, nuclear change of the atoms of the elements also increses. Therefore, the ionization energy of second period elements increses in the following order:

Be < Li < B < C < N < O < F < Ne

The exceptional first ionization energy trends for beryllium generally explained by a completely filled 2s orbital of the beryllium (1s²2s²) atom. However, the exceptional first ionization energy of nitrogen can be explained by the half-filled 3p orbital of the nitrogen (1s²2s²2p³) atom.

On moving down top to bottom in a group, the ionization energy generally decreases due to increased atomic radii of elements. Therefore, the lower member of crystalline solid metals like Ag, Au, Cd, and Hg has lower ionization energy.

The screening or shielding effect is also used to explain the ionization energy variation of elements along a group of the periodic table. Therefore, in many cases, ionization energy from the top to bottom increases due to shielding electron or effective nuclear charges.

Electron Affinity of Elements in Periodic Table

Electron affinity (EA or E) defines the amount of energy released when an electron is added to an isolated gaseous atom in its lowest energy state or ground state to produce an anion.

A (g) + e⁻ → A⁻ (g) + Electron affinity

• When we move down a group, the electron affinity values generally decrease due to steady increses in the atomic radius of the elements. For example, E_Cl > E_Br > E_I.
• Electron affinity values for elements generally increase when moving from left to right in a period of the periodic table.

The exception trend of electron affinity is also common for periodic table elements. For example, the electron affinity trend of the second-row elements is usually lower than that of the third-row.

Electronegativity of Elements in Periodic Table

The electronegativity of a bonded atom is defined as its relative tendency or ability to attract the shared electron pair towards itself.

• The electronegativity increses when moving from left to right in a period.
• Small atoms also attract electrons more strongly than large ones. When we move down in a group, the size and electropositive character of atoms increase.

Therefore, the most electronegative periodic table elements are present in the top right-hand corner. However, the most electropositive elements are present in the bottom left-hand corner.

Oxidizing and Reducing Properties

When we move from left to right across a period in the periodic table, the oxidizing power of the elements generally increses, and the reducing power decreases.

When we go down in a group, the reducing power of elements increses while the oxidizing power decreases. This fact is due to the size of the atom increses and the ionisation energy decreases. Therefore, the reducing power of group 1 elements or alkali metals is in the following order:

Cs > Rb > K > Na > Li

Similarly, the oxidizing power of halogens decreases in the following order:

F > Cl > Br > I

Periodic Trends of Acid-Base Character

Generally, when moving from left to right in a period, the acidic character of the normal oxides of the elements increases. The change from strongly basic character to strongly acidic character is due to an increase in the electronegativity value of the elements. Therefore, the trends of acidic character for the oxides of group 2 elements are:

Na₂O < MgO < Al₂O₃ < SiO₂ < P₄O₁₀ < SO₃ < Cl₂O₇

Metallic and Non-metallic Character

The periodic table elements having a higher value of electronegativity will be non-metals. However, a lower electronegativity will be a metal.

Thus, the metallic character in a period decreases from left to right but it can increase from top to bottom in a group.

Periodic Table with Electron Configuration

When a pair of elements is arranged diagonally to each other in the period table, it describes simple relations or chemical properties like the electric polarization in chemistry. For example, diagonal pairs like beryllium and aluminum have a similar change/size ratio.

Since the size increases in the lower period while the charge increases to the right. However, this rule can not work completely for all the periodic table elements.

Interesting facts in the periodic table also explain the common connection between electronic structure and periodic accommodation capacities of chemical elements in short form.

For example, the 1s orbital can have only two electrons, hence period one contains only two elements. Period 6 elements also contain 6s, 4f, 5d, and 6p orbitals in their electronic structure. Therefore, period 6 contains a total of (2 + 14 + 10 + 6) = 32 elements from cesium to radon.

Such a simplified scientific formula in chemistry is generally used to calculate the number of chemical elements in each period of the periodic table families.

Importance of Periodic Table in Chemistry

• The periodic table is important in chemistry because it provides a tabular display of chemical elements on the basis of atomic number and electronic configuration.
• It also provides trends in element properties like electronegativity, ionization energy, atomic radius, and oxidizing and reducing properties. Therefore, it provides quick information about chemical elements.
• The periodic table can be used during the prediction of properties of undiscovered chemical elements.