Notes on Atoms and Elements

Chemistry: An Introduction to General, Organic, and Biological Chemistry

Elements and Symbols

• Defined as pure substances

• Cannot be broken down into simpler substances

• Listed in the periodic table

• Example: Aluminum (Al)

Chemical Symbols

• One- or two-letter abbreviations for elements.

• Two-Letter Symbols: The second letter is lowercase (e.g., Co for cobalt, not CO which stands for carbon and oxygen)

• Key Symbols:

  • C: Carbon

  • Co: Cobalt

  • S: Sulfur

  • Si: Silicon

  • N: Nitrogen

  • H: Hydrogen

Origin of Element Names

• Derived from various sources: planets, mythological figures, minerals, colors, and famous figures.

Examples:

• Gold: Au (from aurum)

• Silver: Ag (from argentum)

Toxicity of Mercury (Hg)

• Liquid at room temperature, enters the body through:

  • Inhalation

  • Skin contact

  • Contamination in food/water

• Long-term exposure effects:

  • Destroys proteins

  • Disrupts cell function

  • Damages brain and kidneys

The Periodic Table

• Organizes 118 elements by increasing atomic mass.

• Concept introduced by Dmitri Mendeleev in 1869.

  • Elements arranged by increasing atomic mass and grouped by similar properties.

• Groups: Vertical columns (e.g. Alkali Metals, Alkaline Earth Metals, Halogens, Noble Gases).

• Periods: Horizontal rows (7 total).

Classification of Elements

• Metals::

  • Most are shiny, ductile, and malleable.

  • Good conductors of electricity and heat.

• Nonmetals:

  • Generally not shiny, poor conductors.

  • Examples: H, C, N, O, Cl, S.

• Metalloids:

  • Exhibit properties of both metals and nonmetals (e.g., Si, Ge).

Macrominerals Essential for Body

• Four elements make up 96% of body mass: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N).

• Others include Calcium, Phosphorus, Potassium, Sodium, Magnesium, etc.

Microminerals (Trace Elements)

• Essential in small amounts; deficiencies can cause health issues.

• Include some transition elements.

Atomic Structure

• Atoms consist of:

  • Nucleus: Contains protons (+) and neutrons (0).

  • Electrons (-) orbiting in a cloud around the nucleus.

• Subatomic Particles:

  • Proton: positive charge (mass ≈ 1 amu)

  • Neutron: no charge (mass ≈ 1 amu)

  • Electron: negative charge (mass ≈ 0.00055 amu)

Atomic Mass

• Measured in atomic mass units (amu); based on the isotope Carbon-12.

• Mass Number: Protons + Neutrons.

  • Example: Potassium with mass number 39, atomic number 19 ⇒ $39 - 19 = 20 ext{ neutrons}$.

Isotopes

• Different mass numbers with the same number of protons but variable neutrons.

• Atomic symbol representation includes mass number and atomic number.

Trends in the Periodic Table

• Atomic Size: Increases down a group, decreases across a period.

• Ionization Energy: Energy to remove an outermost electron; decreases down a group, increases across a period.

• Metallic Character: Higher in metals (left side), lower in nonmetals (right side).

Lewis Symbols

• Are a method to represent valence electrons using dots around the element symbol.

• Essential for predicting chemical bonding and reactivity.

Conclusion

• Understanding the periodic table and atomic structure is fundamental to chemistry and its applications in various fields, including health and material science.

Chemistry notes introduce elements as pure, unchangeable substances, each represented by unique one or two-letter symbols (e.g., Al, Co). Element names often derive from planets, mythology, or other sources (e.g., Au for gold, Ag for silver).

The periodic table, conceptualized by Dmitri Mendeleev, organizes 118 elements by increasing atomic mass and similar properties, featuring vertical columns known as Groups and horizontal rows called Periods. Elements are broadly classified into Metals (shiny, ductile, malleable, good conductors), Nonmetals (generally not shiny, poor conductors like H, C, O), and Metalloids (exhibiting properties of both, like Si).

Key elements for body mass include Macrominerals (O, C, H, N making up 96%, plus Ca, P, K, Na, Mg) and Microminerals (trace elements essential in small amounts).

Atoms consist of a nucleus containing protons (positive, $\approx 1 \text{ amu}$) and neutrons (no charge, $\approx 1 \text{ amu}$), surrounded by orbiting electrons (negative, $\approx 0.00055 \text{ amu}$). Atomic mass is measured in atomic mass units (amu) based on Carbon-12, with the mass number representing the sum of protons and neutrons. Isotopes are variants of an element with the same number of protons but differing neutrons, leading to different mass numbers.

Periodic table trends include atomic size (increases down a group, decreases across a period), ionization energy (decreases down a group, increases across a period), and metallic character (higher on the left for metals, lower on the right for nonmetals). Lewis Symbols visually represent valence electrons, crucial for understanding chemical bonding. Additionally, the notes highlight the toxicity of mercury (Hg), emphasizing its entry into the body via inhalation, skin contact, or contamination, leading to protein destruction and damage to the brain and kidneys upon long-term exposure.

Overall, understanding the periodic table, atomic structure, and element properties is foundational for chemistry and its biological and material science applications.