Chap 3 Electronic Structure and Periodic Law: The Periodic Table and Element Properties

Electronic Structure and Periodic Law

Course Objectives

This section introduces the foundational concepts of the periodic table, including the classification of elements by groups and periods, and the prediction of element properties based on periodic trends.

• Classify elements in the periodic table by group (vertical columns) and period (horizontal rows).

• Categorize elements into major groups and families based on chemical properties.

• Predict properties of elements using periodic trends such as electronegativity and ionization energy.

The Periodic Table

History and Organization

The periodic table is a systematic arrangement of all known chemical elements, organized by increasing atomic number and recurring chemical properties. Dmitri Mendeleev (1834–1907) was instrumental in its development, arranging elements by atomic weight and observing periodic trends.

• Dmitri Mendeleev arranged elements by atomic weight, leading to the discovery of periodicity in properties.

• Groups are vertical columns where elements share similar chemical properties (e.g., halogens in Group 7).

• Periods are horizontal rows, corresponding to the number of electron energy levels in atoms.

• Properties of elements within a group tend to recur periodically.

Structure of the Periodic Table

The periodic table is organized into columns (groups/families) and rows (periods), reflecting similarities in chemical behavior and electron configuration.

• Groups: Elements in the same group have similar valence electron configurations and chemical properties.

• Periods: Elements in the same period have the same number of electron shells.

Major Sections of the Periodic Table

Elements are classified into several major categories based on their properties and location in the table.

Section	Examples	Key Properties
Alkali Metals	Li, Na, K	Highly reactive, 1 valence electron
Alkaline Earth Metals	Be, Mg, Ca	Reactive, 2 valence electrons
Transition Metals	Fe, Cu, Zn	Variable oxidation states, good conductors
Halogens	F, Cl, Br, I	Very reactive nonmetals, form salts
Noble Gases	He, Ne, Ar	Inert, full valence shell
Other Metals	Al, Sn, Pb	Less reactive, metallic properties
Nonmetals	C, N, O	Poor conductors, various states
Metalloids	B, Si, As	Intermediate properties
Rare Earth Elements	La, Ce, Nd	Lanthanides and actinides, specialized uses

Classification of Elements

Metals, Nonmetals, and Metalloids

Elements are broadly classified based on their physical and chemical properties.

• Metals: Usually solids at room temperature (except Hg), good conductors, malleable, ductile, shiny. Tend to lose electrons in reactions.

• Nonmetals: Can be solids, liquids, or gases; poor conductors; brittle; tend to gain electrons in reactions.

• Metalloids: Exhibit properties intermediate between metals and nonmetals; e.g., silicon is shiny but does not conduct electricity well.

Examples: - Helium (He) is a nonmetal. - Copper (Cu) is a metal. - Arsenic (As) is a metalloid.

Phases of the Elements

States at Room Temperature

Elements exist in different phases (solid, liquid, gas) at room temperature, which can be predicted from their position in the periodic table.

Element	Melting Point (°C)	Boiling Point (°C)
Fluorine	-220	-188
Chlorine	-101	-34
Bromine	-7	59
Iodine	114	184
Astatine	302	337

Periodic Trends

Ionization Energy

Ionization energy is the energy required to remove an electron from a gaseous atom or ion. It is a key periodic trend that helps predict element reactivity.

• Across a period (left to right): Ionization energy increases due to stronger nuclear attraction.

• Down a group (top to bottom): Ionization energy decreases as electrons are farther from the nucleus.

Equation:

$\text{M(g)} + IE \rightarrow \text{M}^+(g) + e^-$

Example: Lithium's first ionization energy: $\text{Li(g)} + IE \rightarrow \text{Li}^+(g) + e^-$

Order of ionization energy for halogens: $\text{Cl} > \text{Br} > \text{I}$

Electronegativity

Electronegativity is a measure of an atom's ability to attract electrons in a chemical bond. It follows predictable trends in the periodic table.

• Highest electronegativity: Fluorine (F), with a value of 4.0.

• Trend: Increases across a period, decreases down a group.

Element Groups and Their Importance

Biological and Practical Significance

Certain elements are essential for biological processes and practical applications.

• Major elements in the human body: C, H, O, N, Ca, P, K, S, Na, Cl, Mg, Fe, Zn, I, Se, Cu, Mn, F, Cr, Mo, Co.

• Common ions in the body: Na+, K+, Ca2+, Mg2+, Cl-, HCO3-.

• Elements for bone health: Ca, P, Mg, F.

• Elements for oxygen transport: Fe (in hemoglobin).

• Radioactive tracers: I, Tc, Co.

• Currency and measurement: Au (gold), Hg (mercury in barometers).

Summary Table: Classification of Elements

Type	Physical Properties	Chemical Properties	Examples
Metals	Solid (except Hg), shiny, malleable, ductile, good conductors	Tend to lose electrons, form cations	Fe, Cu, Zn, Na
Nonmetals	Solid, liquid, or gas; dull, brittle, poor conductors	Tend to gain electrons, form anions	O, N, Cl, S
Metalloids	Intermediate properties; semi-conductors	Can gain or lose electrons	B, Si, As

Key Terms

• Group (Family): Vertical column in the periodic table.

• Period: Horizontal row in the periodic table.

• Ionization Energy: Energy required to remove an electron from an atom.

• Electronegativity: Ability of an atom to attract electrons in a bond.

• Metals, Nonmetals, Metalloids: Major classifications of elements based on properties.

Additional info: Some context and examples have been expanded for clarity and completeness, including biological relevance and practical applications of elements.