BIOS 111: 1/21/25

Introduction

  • Memorizing key concepts in organic chemistry, biochemistry, and cell biology is essential for success.

  • Focus on understanding and familiarity with important elements and electronegativity values.

Historical Context

  • Discussion of fundamental elements dates back to Greek philosophers.

    • Democritus: Introduced the idea that matter is made of unchangeable particles (atoms).

    • Heraclitus: Suggested that ideas and thoughts (logos) hold the universe together, not just matter.

The Bohr Model

  • The Bohr model is a simplified representation of how atoms function and interact.

    • Focuses on protons and electrons being fundamental to an atom’s identity.

    • Atomic identity is defined by the number of protons in the nucleus. E.g., Helium has 2 protons.

    • Neutrons and electrons are less significant in determining the type of element.

Elements of Biological Significance

  • Key elements that make up biological systems:

    • Major Elements: Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N).

    • Other Important Elements: Phosphorus (P), Sulfur (S), and Iron (Fe).

    • Focus primarily on elements in the first four rows of the periodic table.

Electron Configuration and Reactivity

  • Electron shells and their capacity:

    • First Shell: Can hold up to 2 electrons (e.g., Helium).

    • Higher Shells: Want to fill to 8 for stability, which dictates chemical reactivity.

  • Noble gases (e.g., Helium, Neon) are not reactive due to filled electron shells.

  • Other elements may be highly reactive depending on their electron arrangements, wanting to gain, lose, or share electrons to fill their outer shell.

Isotopes and Atomic Mass

  • Isotopes: Variants of elements with the same number of protons but different numbers of neutrons (e.g., P-32 has different neutrons).

  • Atomic mass can differ due to the presence of isotopes, representing an average.

Electrons and Chemical Bonds

  • Electrons do not move freely; they occupy specific orbitals around the nucleus.

  • Understanding atomic shape is essential, as it influences how atoms interact with others.

  • Covalent bonds form when nonmetals share electrons to fill outer shells.

    • Example: Two hydrogen atoms form H₂ to share electrons.

Electronegativity

  • Electronegativity refers to an atom's ability to attract electrons in a chemical bond, rated on a scale (1 to 4).

    • Fluorine (4) is the most electronegative and attracts electrons strongly.

    • Carbon (2.5) shares electrons unevenly with hydrogen.

  • Polar covalent bonds occur when there is a significant difference in electronegativity between atoms (e.g., O-H in water is polar).

Covalent Bonds and Polarity

  • Non-Polar Covalent Bonds: Equal sharing of electrons, as seen in H₂.

  • Polar Covalent Bonds: Unequal sharing causes partial charges on molecules (e.g., water has a slight negative charge near the oxygen).

    • Rule of thumb: A significant difference (>0.5) in electronegativity indicates a polar bond.

Conclusion

  • Understanding atomic structure, electronegativity, and types of bonds is essential for studying organic chemistry and related fields.

  • Focus on memorizing key elements and their properties, as they will be fundamental in understanding biological systems.

LEARNING GOALS

Properties of Atoms and Subatomic Particles

  • Atoms consist of protons, neutrons, and electrons.

  • Protons are positively charged and define the atomic number and identity of the element.

  • Neutrons are neutral particles found in the nucleus that add mass but do not affect charge.

  • Electrons are negatively charged and occupy specific orbitals around the nucleus.

Differentiate Metals from Non-Metals

  • Metals:

    • Typically have a shiny appearance, are malleable, ductile, and good conductors of heat and electricity.

    • Tend to lose electrons during chemical reactions.

  • Non-Metals:

    • Usually dull, brittle, and poor conductors of heat and electricity.

    • Tend to gain or share electrons during chemical reactions.

Define Isotope

  • An isotope is a variant of an element that has the same number of protons but a different number of neutrons.

  • Example: P-32 has a different neutron count compared to other forms of phosphorus, affecting its atomic mass.

The "Rule of 8" and Electron Shells

  • The rule of 8 refers to the tendency of atoms to prefer having 8 electrons in their outer shell for stability (octet rule).

  • First Shell: Can hold up to 2 electrons (e.g., Helium).

  • Higher Shells: Prefer to have 8 electrons to achieve stability and dictate chemical reactivity.

Define and Give Examples of Covalent Bonds

  • Covalent bonds form when nonmetals share electrons to fill their outer electron shells.

  • Example: Two hydrogen atoms can share their electrons to form H₂, thus filling their outer shells.

Define Electronegativity and Know Common Elements Values

  • Electronegativity is the measure of an atom's ability to attract and hold onto electrons in a chemical bond.

  • It is rated on a scale of 1 to 4, with fluorine being the most electronegative at 4.

  • Common Elements Values:

    • Fluorine: 4

    • Carbon: 2.5 (shares electrons unevenly with hydrogen)

    • Example of polar covalent bond: O-H in water due to a significant difference in electronegativity.