Chemistry in Living Systems Flashcards

Essential Elements of Life

• Carbon (C), Oxygen (O), Hydrogen (H), Nitrogen (N)
• Organic compounds are carbon-based.
• These elements constitute 96% of living matter.
• Other elements include Calcium (bones, muscle contractions) and Sodium/Potassium (nervous system, electrolytes).

Atoms and Elements

• All matter is composed of atoms.
• Atoms consist of:
  • Nucleus: Protons (p^+) and Neutrons (n^0) contribute to mass.
  • Electrons: (e^-) Orbit in clouds/shells with negligible weight.

Elements & Periodic Table

• Atomic number: Number of protons (p^+) or electrons (e^-).
• Atomic mass: Sum of protons (p^+) and neutrons (n^0).
• Number of neutrons (n^0) = Atomic mass - Number of protons (p^+) (atomic #)
• Groups (1-18): Indicate valence electrons.
• Periods (1-7): Indicate the number of shells.

Trends in Periodic Table

• Atomic Radius: Size of atom (nucleus to valence shell).
• Ionization Energy: Energy to remove an electron from its atom.
• Electronegativity: Energy to attract nearby electrons.
• Trends:
  • Atomic Radius increases with more electron shells and decreases with more nuclear pull.
  • Ionization Energy increases across a period and decreases down a group.
  • Electronegativity increases across a period and decreases down a group.

Isotopes

• Different variations of an element with different numbers of neutrons (n^0).
• Same number of protons (p^+) and electrons (e^-), but different weights.
• Chemically behave the same (same number of electrons).

Radioactive Isotopes

• Unstable nucleus decays spontaneously.
• Decay results in a different element.

Radioactive Dating

• Decay of radioactive isotopes is mapped to determine fossil age.
• Half-life: Time for half of the radioactive element to decay into another element.
• Scientists identify age of fossil using half-life of atom

Radioactive Tracers

• Used to follow chemicals through reactions and trace their path.
• Radioactive isotopes release energy as they decay.

Energy Levels of Electrons

• Electrons have potential energy.
• Electrons absorb energy to move to an excited state and release energy to return to the ground state.

Importance of Electrons

• Shell 1 holds 2 electrons (e^-).
• Other shells hold 8 electrons (e^-).
• Lewis dot diagrams show valence electrons.
• Octet rule: Atoms gain/lose/share electrons to achieve 8 electrons in the valence shell.

Forming Compounds

• Compounds contain at least two different kinds of atoms (e.g., H_2O).
• Bonds involve sharing/transfer of electrons.

Ionic Bonds

• Occur between a metal and a non-metal.
• Involve electron transfer.
• Ions: Positive charge (cation) and negative charge (anion).
• Strong bond (crystal lattice).

Covalent Bonds

• Occur between two non-metals.
• Involve sharing of electrons.
• Can be single, double, or triple bonds.

Bond Enthalpies

• Amount of energy needed to break a bond.
• Multiple bonds are stronger than single bonds.

Types of Covalent Bonds

• Polar: Unequal sharing of electrons.
• Non-Polar: Equal sharing of electrons.

Electronegativity (EN)

• Pauling Scale (0.7-4.0).
• EN difference: 0-0.5 = non-polar, 0.51-1.70 = polar, 1.71+ = ionic.

Electronegative Notations

• Partial charge notation (δ+ and δ-).
• Bond dipole arrows.

The Role of Chemistry in Biology

• Life depends on chemical reactions.
• Chemistry explains molecular interactions, structure/function of biomolecules, and energy production in metabolism.

How Electronegativity Affects Biology

• Nonpolar bonds: Found in lipids, creating hydrophobic molecules.
• Polar bonds: Found in water, proteins, DNA.
• Molecular polarity influences solubility, protein folding, and cell membrane structure.