Chapter 5: Periodic Table Lecture Notes

Vocabulary flashcards covering the historical development, laws, classifications, and periodic trends of the periodic table based on Chapter 5 lecture notes.

Classification of Elements (Purpose)

Organizing elements so that the study of elements and correlating their properties becomes easier and more systematic.

Prout's Hypothesis (William Prout)

The postulation based on the discovery of atomic masses stating that two different elements can never have the same atomic mass.

Dobereiner's Triad

A group of three chemically similar elements arranged in increasing order of atomic mass, where the atomic mass of the middle element is approximately equal to the arithmetic mean of the other two elements.

Law of Triads

The rule stating that when elements with similar physical and chemical properties are placed in groups of three in order of increasing atomic masses, the atomic mass of the middle element is approximately equal to the average of the atomic masses of the other two elements.

Newlands' Law of Octaves

The law stating that when elements are arranged in increasing order of atomic masses, the properties of every eighth element are a repetition of the properties of the first element.

Mendeleev's Periodic Law

The principle stating that the physical and chemical properties of elements are a periodic function of their atomic masses, giving first preference to properties and second preference to atomic masses.

Eka-Aluminium and Eka-Silicon

Names given by Mendeleev to undiscovered elements whose properties he predicted, later identified respectively as Gallium and Germanium.

Anomalous Pairs

Pairs of elements in Mendeleev's periodic table arranged contrary to the order of increasing atomic masses, namely: $\text{Ar}$ ($40$) before $\text{K}$ ($39$), $\text{Co}$ ($58.9$) before $\text{Ni}$ ($58.6$), and $\text{Te}$ ($127.6$) before $\text{I}$ ($126.9$).

Henry Moseley's Discovery

The scientific conclusion that atomic number, rather than atomic mass, is the most fundamental property of an element.

Modern Periodic Law

The fundamental law stating that the physical and chemical properties of elements are a periodic function of their atomic numbers.

Periodicity

The repetition of similar physical and chemical properties of elements after regular intervals (whether they increase, decrease, or remain the same).

Cause of Periodicity

The recurrence of similar electronic configurations in the valence shell of atoms after regular intervals.

Periods

The seven horizontal rows in the periodic table, where the period number is equal to the number of electron shells in the atom.

Groups

The vertical columns in the periodic table containing elements with the same number of valence electrons and the same valency.

Representative Elements

Elements belonging to Group 1, Group 2, and Groups 13 to 17 that possess only one incomplete outermost electron shell.

Transition Elements

Heavy metallic elements in Groups 3 to 12 characterized by having two incomplete outermost shells, variable valencies, catalytic properties, and the ability to form coloured ions and compounds.

Inner Transition Elements

Elements belonging to Group 3 that are divided into the Lanthanide series (Period 6, starting with Lanthanum) and the Actinide series (Period 7, starting with Actinium), placed separately at the bottom of the table.

Chalcogens

The common name for elements of Group 16 (the Oxygen family), meaning 'ore-formers.'

Halogens

Group 17 non-metallic elements ($\text{F}$, $\text{Cl}$, $\text{Br}$, $\text{I}$, $\text{At}$) with 7 valence electrons and a valency of $-1$, whose name means 'salt-formers' because they react with metals to form salts.

Rare Earth Elements

An alternative name given to the Lanthanide series of elements.

Typical Elements

The elements of the 3rd period ($\text{Na}$, $\text{Mg}$, $\text{Al}$, $\text{Si}$, $\text{P}$, $\text{S}$, $\text{Cl}$) that summarize the properties of their entire respective groups.

Bridge Elements

Second-period elements that exhibit a diagonal resemblance in properties to the third-period element placed diagonally opposite to them.

Diagonal Relationship

The resemblance in chemical and physical properties between an element in the 2nd period and the element placed diagonally to the right in the 3rd period.

Atomic Size

The distance measured between the center of the nucleus and the outermost electron shell of an isolated atom.

Nuclear Charge

The total positive charge in an atom's nucleus, determined by the number of protons ($p^+$), which increases from left to right across a period.

Alkali Metals

Highly reactive Group 1 metals ($\text{Li}$, $\text{Na}$, $\text{K}$, $\text{Rb}$, $\text{Cs}$, $\text{Fr}$) with 1 valence electron that react vigorously and explosively with water to form strong alkaline solutions.

Alkaline Earth Metals

Group 2 metals ($\text{Be}$, $\text{Mg}$, $\text{Ca}$, $\text{Sr}$, $\text{Ba}$, $\text{Ra}$) having a valency of 2, whose oxides are found in the Earth's crust and are alkaline in nature.

Zero Group (Noble Gases)

Group 18 elements ($\text{He}$, $\text{Ne}$, $\text{Ar}$, $\text{Kr}$, $\text{Xe}$, $\text{Rn}$) discovered by William Ramsay that have a completely filled outermost shell, zero valency, and are chemically inert.

Caesium Fluoride ($\text{CsF}$)

The chemical compound formed between the most metallic element ($\text{Cs}$) and the most non-metallic element ($\text{F}$), exhibiting the most ionic character.