Periodic Table and Lithium

Mid-1800s: Medical community links uric acid to various maladies.
Lithium carbonate solutions were found to dissolve uric acid, leading to therapeutic preparations containing lithium carbonate salt.
Non-medical companies added lithium to soft drinks.
1940s: Doctors recommend salt-restricted diets for cardiac patients.
Lithium chloride was commercially available as a sodium chloride table salt substitute.
Reports of severe poisonings and deaths due to lithium overdosing led to US companies withdrawing lithium salts from the market.
Australian psychiatrist John Cade proposed using lithium salts to treat mania, with successful clinical trials.
Lithium carbonate became commonly prescribed in Europe for manic behavior.
1970: US Food and Drug Administration approved lithium carbonate for manic symptoms.
Lithium (Li) has an atomic number of 3.
It is a soft alkali metal and the least dense solid element under standard conditions (specific gravity = 0.53).
Lithium is highly reactive and found only in salt compounds.

1869: Dmitry Mendeleev published his periodic table, arranging elements by atomic weight to reveal recurring physical and chemical properties.
Revised periodic table organizes elements by increasing atomic number (number of protons).
The periodic table represents the periodic law: chemical and physical properties of elements depend on their atomic numbers.
Elements are arranged into periods (rows) and groups/families (columns) based on atomic number.
There are seven periods, corresponding to the principal quantum numbers $n = 1$ through $n = 7$ for the s and p block elements.
Each period fills sequentially, with each element having one more proton and electron than the element to its left.
Groups contain elements with the same electronic configuration in their valence shell, sharing similar chemical properties.

Valence electrons are farthest from the nucleus and have the highest potential energy.
They participate in chemical bonds with other atoms' valence electrons.
Valence shell electrons determine chemical reactivity and properties of an element.
Roman numerals above each group indicate the number of valence electrons in that group's elements.

Elements are separated into two classes using the letters "a" and "b" alongside Roman numerals.
- A elements: Representative elements (groups 1A through 8A) with valence electrons in s or p subshells.
- B elements: Non-representative elements, including transition elements (valence electrons in s and d subshells) and lanthanide/actinide series (valence electrons in s and f subshells).
Representative elements' electron configuration is determined by the Roman numeral and letter designation (e.g., Group 5A has 5 valence electrons with configuration $s^2p^3$ ).
Non-representative elements may have unexpected electron configurations (e.g., Chromium $\text{Cr}$ : $4s^13d^5$ , Copper $\text{Cu}$ : $4s^13d^{10}$ ).
Modern IUPAC system numbers groups 1 to 18 without A and B subdivisions.