Study guide: Periodic Table and Periodicity

📋 Course Outline

1. Periodic Table Organization
2. History and Classification Principle
3. Periods One Through Three
4. Periods Four and Five
5. Periods Six and Seven
6. Groups and Valence Electrons

📖 1. Periodic Table Organization

🔑 Key Concepts & Definitions

• Periodic table: An arrangement of chemical elements by atomic number and by the recurring chemical and physical properties associated with their positions.

★ Must-know

📌 Periods are horizontal rows corresponding to the number of electron shells, whereas groups or families are vertical columns whose elements share similar properties due to their external electron configuration.

Further detail

• The periodic table is generally divided into four blocks: s, p, d, and f.

• The table's organization helps explain trends in electronegativity, atomic radius, and ionization energy and helps predict element behavior.

💡 Memory Hook

Periods run horizontally; groups run vertically.

📖 2. History and Classification Principle

★ Must-know

• Mendeleev observed sequences in the properties of elements, establishing the idea of periodicity. - Mendeleïev

• In 1913, Moseley discovered the atomic number Z, establishing it as the most important criterion for periodic classification.

📌 Modern periodic classification arranges elements in increasing order of atomic number.

Further detail

• Dimitri Mendeleev proposed an early form of the periodic table and arranged the 63 elements known in his time in increasing order of atomic mass. - Dimitri Mendeleïev, 1834–1907

📖 3. Periods One Through Three

★ Must-know

• The periodic table has seven periods, and the first three periods are short.

• The second period contains eight elements, from lithium to neon, whose electrons occupy two energy levels.

• The third period runs from sodium (Z = 11) to argon (Z = 18), and its 3s and 3p subshells fill progressively.

Further detail

• The first period corresponds to filling the 1s subshell and contains hydrogen and helium; helium has a filled 1s orbital.

• Neon has two electrons in the 2s subshell and six electrons in the 2p subshell.

📖 4. Periods Four and Five

★ Must-know

• The fourth period contains 18 elements whose electrons occupy four energy levels.

• The fifth period contains 18 elements and resembles the fourth period.

Further detail

• In the fourth period, the 3d subshell fills progressively from scandium (Z = 21) to zinc (Z = 30).

• Chromium (Z = 24) has the configuration 4s¹ 3d⁵ rather than the expected 4s² 3d⁴.

• Copper (Z = 29) has the configuration 4s¹ 3d¹⁰ rather than the expected 4s² 3d⁹.

• The fifth-period transition series runs from yttrium to cadmium as the 4d subshell fills progressively.

• In palladium, the 5s² subshell empties to allow all 4d orbitals to become filled, which gives the metal greater stability.

📖 5. Periods Six and Seven

★ Must-know

• The sixth period contains 32 elements and involves the beginning of electron occupation of the sixth energy level.

• The sixth-period lanthanides comprise 14 elements from cerium (Z = 58) to lutetium (Z = 71), with progressive filling of the 4f subshell.

• The seventh period is incomplete, and its seventh energy level contains at most eight elements of subgroup A.

• The actinides form a series of 14 transition elements following the naturally occurring element actinium (Z = 89), with progressive filling of the 5f subshell.

Further detail

• The sixth period also includes 10 ordinary transition elements in which the 5d subshell fills, followed by the noble gas radon.

• Only the first six elements of the seventh period occur naturally; the others have been synthesized.

• The lanthanides, together with scandium and yttrium, constitute the rare earths; the lanthanides and actinides form subgroup C, and their chemical properties are so similar that separation is difficult.

📖 6. Groups and Valence Electrons

🔑 Key Concepts & Definitions

• Valence electrons: The electrons in the outermost shell that give an atom or element its chemical properties, including its ability to bond with other atoms.
• Family or group: A set of elements with the same number of electrons in the peripheral shell, with groups designated by Roman numerals corresponding to their numbers of valence electrons.

★ Must-know

• Elements in the same column have the same number of electrons in their outermost shell.

Further detail

• Groups are subdivided into two subgroups, A and B.

• The periodic table contains 16 element families across 18 columns because group VIII B occupies three columns.

• Subgroup A comprises metals, nonmetals, and noble gases and consists of eight families arranged according to progressive filling of the peripheral shell.