Classification of Elements & Periodicity in Properties Flashcards

Comprehensive vocabulary flashcards covering the history of periodic classification, periodic table structure, and periodic properties like atomic size, ionization energy, and effective nuclear charge.

Dobereiner Triads

A classification where elements are arranged in groups of three (Triads) with similar properties, such where the atomic weight of the middle element is the average of the other two.

Newlands Octave Rule

The principle that when elements are arranged in increasing order of atomic weights, every eighth element has properties similar to the first, just like musical octaves; this rule is only true up to calcium ($Ca$).

Lothar Meyer Curve

A plot of physical properties such as atomic volume, melting point, and boiling point against atomic weight, which displays a periodically repeated pattern.

Mendeleev's Periodic Law

The principle stating that the physical and chemical properties of elements are a periodic function of their atomic weights.

Modern Periodic Law

The principle established by Henry Moseley stating that the physical and chemical properties of the elements are periodic functions of their atomic numbers ($Z$).

s-Block Elements

Elements where the last electron enters the s sub-shell, including Alkali metals (Group 1, $ns^1$) and Alkaline earth metals (Group 2, $ns^2$).

p-Block Elements

Elements where the last electron enters the p sub-shell, encompassing Groups 13 to 18 with a general electronic configuration of $ns^2 np^{1-6}$.

Representative Elements

Elements belonging to the s-block and p-block (excluding noble gases in some contexts), also known as main group elements.

d-Block Elements

Also known as Transition elements, these are elements where the last electron enters the $(n-1)d$ sub-shell, with a general configuration of $(n-1)d^{1-10} ns^{0-2}$.

f-Block Elements

Also known as Inner transition elements, these are elements where the last electron enters the $(n-2)f$ sub-shell, including Lanthanoids ($4f$) and Actinoids ($5f$).

Screening Effect (Shielding Effect)

The repulsive force exerted by inner electrons ($s > p > d > f$) on outer electrons, which reduces the effective attraction between the nucleus and the target electron.

Effective Nuclear Charge ($Z_{eff}$)

The net attractive power of the nucleus exerted on an outer test electron after accounting for the screening effect $(\sigma)$, calculated as $Z_{eff} = Z - \sigma$.

Diagonal Relationship

A phenomenon where diagonally adjacent elements of the 2nd and 3rd periods, such as $Li$ and $Mg$, exhibit similar chemical properties due to similar ionic potential (charge/size ratio).

Covalent Radius

Half of the internuclear distance between two singly bonded atoms of the same element, typically defined for non-metals.

Van der Waals Radius

Half the distance between the nuclei of two non-bonded nearest neighboring atoms of the same element in its solid state; it is larger than covalent and metallic radii.

Lanthanide Contraction

A decrease in atomic and ionic size due to the poor shielding of $4f$ electrons, causing an increase in $Z_{eff}$ in the 5d series elements, making them similar in size to 4d series elements.

Ionization Energy (IE)

The minimum energy required to remove the most loosely bounded electron from an isolated gaseous atom.

Electron Gain Enthalpy ($\Delta H_{eg}$)

The enthalpy change that occurs when an electron is added to a neutral gaseous atom to convert it into a negative ion. It is exothermic for most neutral atoms but endothermic for noble gases and elements like $N$, $Be$, and $Mg$.

Electron Affinity (EA)

The amount of energy released when an electron is added to an isolated gaseous atom; generally, $EA \approx -\Delta H_{eg}$.

Electronegativity (EN)

A qualitative measure of the ability of an atom in a chemical compound to attract shared electrons to itself.

Amphoteric Oxides

Oxides or hydroxides that can act as both an acid and a base, such as $Al_2O_3$, $ZnO$, $PbO$, and $BeO$.

Neutral Oxides

Oxides that do not show acidic or basic character, such as $NO$, $N_2O$, $CO$, and $H_2O$.