General Chemistry Study Notes: Elements, Water Treatment, and UV Disinfection

Discovery of New Elements

Possibility of Finding New Elements

The periodic table is a foundational tool in chemistry, organizing all known chemical elements by their atomic number, electron configuration, and recurring chemical properties. The search for new elements continues, especially at the far end of the table, where superheavy elements are synthesized in laboratories.

• Element Discovery: New elements are typically created in particle accelerators by colliding lighter nuclei.

• Superheavy Elements: Elements beyond uranium (atomic number 92) are called transuranium elements and are not found naturally on Earth.

• Periodic Table Expansion: The periodic table has grown as new elements have been discovered, with recent additions such as elements 113 (Nihonium), 114 (Flerovium), 115 (Moscovium), 116 (Livermorium), 117 (Tennessine), and 118 (Oganesson).

• Element 120: Theoretical predictions suggest that element 120 may be within reach, but its synthesis is challenging due to instability and short half-lives.

Example: The discovery of element 118 (Oganesson) required international collaboration and advanced technology.

Additional info: The periodic table is color-coded to show the age of discovery, with different periods marked for scientific revolutions and technological advances.

Wastewater Treatment

Steps in Wastewater Treatment

Wastewater treatment is a multi-step process designed to remove contaminants from water before it is released back into the environment. Each step targets specific types of waste or microorganisms.

• Collection: Wastewater is collected from homes, businesses, and industries.

• Head Works: Removal of large trash and objects.

• Screening: Removal of easy stuff (organic solids) that can be used as fertilizers.

• Primary Treatment: Settling tanks allow heavier solids to settle out.

• Secondary Treatment: Biological treatment to "eat" anything else, using bacteria to digest organic matter.

• Polishing Filters: Removal of remaining bacteria physically.

• Disinfection: Bacteria-killing step, often done via ultraviolet (UV) light or chemical disinfectants like chlorine compounds.

Example: In Stevens Point, UV light is used for the final disinfection step.

Ultraviolet (UV) Light and DNA Disruption

UV Light Interaction with DNA

Ultraviolet light is divided into three types based on wavelength: UVA, UVB, and UVC. UVC is the most effective for disinfection because it has the shortest wavelength and highest energy, making it capable of disrupting microbial DNA.

• DNA Bases: DNA consists of four bases: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C).

• UV-Induced Damage: When two thymine bases (T-T) are adjacent, UV light can cause them to form a dimer, disrupting DNA replication and function.

• Energy and Wavelength: The energy required for a T-T dimer to jump to a higher energy state is $7.8 \times 10^{-19}$ J. The wavelength ($\lambda$) of light corresponding to this energy for one photon can be calculated using the equation:

$E = \frac{hc}{\lambda}$ Where: $E$ = energy of photon (J) $h$ = Planck's constant ($6.626 \times 10^{-34}$ J·s) $c$ = speed of light ($3.00 \times 10^8$ m/s) $\lambda$ = wavelength (m)

Example Calculation: To find $\lambda$ for $E = 7.8 \times 10^{-19}$ J:

$\lambda = \frac{hc}{E}$ $\lambda = \frac{6.626 \times 10^{-34} \times 3.00 \times 10^8}{7.8 \times 10^{-19}}$ $\lambda \approx 2.55 \times 10^{-7}$ m = 255 nm

Types of UV Light:

• UVA: 315–400 nm (typical black light, less effective for disinfection)

• UVC: 100–280 nm (most effective for killing bacteria)

Application: UVC bulbs are used in water treatment plants for disinfection.

Chlorine Compounds in Disinfection

Properties and Effectiveness of Chlorine Compounds

Chlorine compounds, such as bleach (sodium hypochlorite), are widely used for disinfection due to their strong oxidizing properties. Their effectiveness can be explained using periodic table trends.

• Periodic Trends: Chlorine is a halogen (Group 17), highly electronegative and reactive.

• Oxidizing Power: Chlorine compounds disrupt microbial cell walls and proteins by oxidation.

• Applications: Used in water treatment, household cleaning, and medical sanitation.

Example: Bleach is used to disinfect surfaces and water by killing bacteria and viruses.

Additional info: The effectiveness of chlorine compounds is due to their ability to accept electrons and form strong bonds, making them potent disinfectants.

Table: Types of UV Light and Their Applications

Type of UV	Wavelength Range (nm)	Application
UVA	315–400	Black lights, tanning beds, less effective for disinfection
UVB	280–315	Sunburn, DNA damage, moderate disinfection
UVC	100–280	Water and air disinfection, most effective for killing microbes