Ch 7Modern Periodic Table — Class 11 Chemistry, concept-first.

In the early nineteenth century, about 30 known elements were sorted into three broad physical-property classes: metals, nonmetals and metalloids.

Although many scientists have proposed different layouts for the periodic table over the years, the 'long form' or 'modern periodic table' — a revised version of Mendeleev's original table built aroun…

Historically, Mendeleev built his periodic table purely from the empirically-observed periodicity of elemental properties, without any knowledge of atomic structure, by arranging elements in increasin…

Along any period, the atomic number increases by exactly one at each step, and the newly added electron always goes into the outermost (valence) shell to form the next neutral atom.

Since a new outermost shell is added every time you step one period further down a group, the elements of a given group are generally expected to share the same general outer electronic configuration…

Section 7.2 already noted that the modern periodic table's overall shape divides into four blocks; this subsection explains WHY, in terms of electronic configuration.

Having established in section 7.2-7.3 that the 118 elements of the modern periodic table distribute across four blocks, each with its own characteristic general electronic configuration, this section…

The s-block consists of group 1 (the alkali metals) and group 2 (the alkaline earth metals). All of these elements are highly reactive metals and, as a result, are never found free in nature — always…

The p-block spans groups 13 to 18. Together with the s-block, its elements are called the 'representative' or 'main group' elements (as opposed to the transition and inner-transition elements of the d…

The d-block spans groups 3 to 12, all of which are metals, commonly called transition elements or transition metals.

All f-block elements are metals, arranged in two horizontal series placed below the main table: the lanthanoid series, running from ₅₈Ce to ₇₁Lu, and the actinoid series, running from ₉₀Th to ₁₀₃Lr.

The periodic table's structure was originally built purely from empirically-observed periodicity — elemental properties recur in a similar way within a group and vary gradually across a period, exactl…

In any multi-electron atom, the positively-charged nucleus attracts every negatively-charged electron around it, while the electrons simultaneously repel one another — and the repulsion exerted specif…

Many physical properties of elements — melting point, boiling point, density among others — show clear periodicity.

The quantum mechanical model describes an atom's extranuclear region as a fuzzy electron cloud with no sharply-defined outer boundary, so 'atomic radius' cannot be measured directly — it has to be EST…

An atom forms a positively-charged ion (a CATION) when it loses one or more electrons, and a negatively-charged ion (an ANION) when it gains one or more electrons.

Removing an electron from a neutral, isolated gaseous atom X in its ground state forms the cation ; the energy that this removal requires is called the ionization enthalpy, , expressed in kJ mol⁻¹.

Adding an electron to a neutral atom X forms the anion ; the enthalpy change accompanying this addition to an isolated gaseous atom in its ground state is called the electron gain enthalpy, , expresse…

When two atoms of different elements form a covalent bond, the shared electron pair is rarely shared perfectly equally — one atom typically pulls it closer to itself.

An element's single most fundamental chemical property is its COMBINING POWER — its capacity to form chemical bonds — expressed numerically as its VALENCY (or valence): the number of chemical bonds an…

For MAIN-GROUP elements specifically, valency is usually equal either to the number of valence (outermost-shell) electrons the atom has, or to the DIFFERENCE between 8 and that number of valence elect…

Metals, nonmetals and metalloids occupy visibly separate regions of the modern periodic table: metals cluster on the left, nonmetals on the right, and metalloids sit along the zig-zag line that divide…

An element's chemical reactivity is governed by how easily it can attain the stable electronic configuration of its nearest noble (inert) gas neighbour, either by gaining or by losing electrons.