Ch__2_Intro_Chem_9e

Chapter 2: The Chemical Context of Life

• Difference between atom, element, and compound:

  • Atom: The smallest unit of matter that retains the properties of an element.

  • Element: A pure substance that cannot be broken down by ordinary means. Examples include hydrogen (H) and nitrogen (N).

  • Compound: A substance formed from two or more different elements combined in a fixed ratio. Examples include water (H2O) and carbon dioxide (CO2).

• Three main components of an atom:

  • Proton: Positive charge (+1), located in the nucleus.

  • Neutron: No charge (0), also located in the nucleus.

  • Electron: Negative charge (-1), found in electron shells surrounding the nucleus.

• Types of bonds:

  • H2O: Polar covalent bond (between H and O).

  • KCl: Ionic bond (between K+ and Cl-).

  • C6H12O6: Covalent bonds (between C, H, and O).

  • N2: Nonpolar covalent bond (between two N atoms).

  • Ba(OH)2: Ionic bond (between Ba2+ and OH-).

Ants & the Duroia Trees

• Ants utilize formic acid to inhibit the growth of other plants, ensuring that Duroia trees remain a suitable habitat.

Key Concepts to Know

• Subatomic particles: Importance of protons, neutrons, and electrons.

• Types of bonds: Mechanism of bond formation and their relative strengths.

Matter vs. Energy

• Matter:

  • Has mass and occupies space.

  • Subject to gravitational forces.

  • Composed of elements and compounds.

• Energy:

  • Facilitates the movement of matter.

  • Exists as potential or kinetic energy.

  • Represents the ability to perform work, interchangeable between forms (e.g., sound, light, heat).

Elements and Compounds

• Element:

  • Defined as a "pure" substance, cannot be deconstructed into simpler substances.

  • Examples include hydrogen (H) and nitrogen (N).

• Compound:

  • Composed of two or more different elements combined in a fixed ratio.

  • Examples include H2O and CO2.

Elements Essential for Life

• Total of 25 elements are vital, constituting 96% of living organisms:

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

  • Other significant elements: Phosphorus (P), Sulfur (S), Calcium (Ca), Potassium (K), and trace elements ( e.g., Iron (Fe), Iodine (I)).

  • Mnemonic: CHNOPS (for the major elements).

Elements of the Human Body

• Table 2.1: Elements and Body Mass Percentages

  • Oxygen (O): 65.0%

  • Carbon (C): 18.5%

  • Hydrogen (H): 9.5%

  • Nitrogen (N): 3.3%

  • Calcium (Ca): 1.5%

  • Phosphorus (P): 1.0%

  • Potassium (K): 0.4%

  • Sulfur (S): 0.3%

  • Sodium (Na): 0.2%

  • Chlorine (Cl): 0.2%

  • Magnesium (Mg): 0.1%

  • Trace elements: (< 0.01% of body mass) including Boron (B), Chromium (Cr), Iron (Fe), etc.

Atomic Structure

• Definition: An atom is the smallest unit of matter retaining the element’s properties.

• Subatomic Particles:

  • Neutrons: 1 dalton, located in nucleus, charge = 0.

  • Protons: 1 dalton, located in nucleus, charge = +1.

  • Electrons: negligible mass, found in shells, charge = -1.

Atomic Number and Mass

• Mass Number: Sum of protons and neutrons (e.g., Helium: 4He, Mass # = 4).

• Atomic Number: Number of protons (and electrons); it defines the element.

Isotopes

• Variations of elements with the same number of protons but different numbers of neutrons.

• Radioactive isotopes: Used in medical diagnostics, can be harmful in uncontrolled exposure.

Types of Chemical Bonds

• Strongest Bonds:

  • Covalent Bonds: Formed by sharing electrons – polar (unequal sharing, e.g., O-H) and nonpolar (equal sharing, e.g., O2).

• Ionic Bonds: Form between ions of opposite charges (e.g., Na+Cl-), influenced by environmental factors (like water).

Weaker Bonds

• Hydrogen Bonds: Attraction between a hydrogen atom of one polar molecule and an electronegative atom of another.

• Van der Waals Interactions: Weak attractions between close atoms or molecules, e.g., gecko toe hairs on a wall surface.

• All bond types are crucial for life; they facilitate quick reactions and cellular processes.

Molecular Shape and Biological Activity

• The shape of molecules is vital ( e.g., natural endorphins vs. morphine) as it determines how they interact with receptors in the body, influencing pain relief and pleasure.

Chemical Reactions

• Basic Concept: Reactants convert into products (e.g., 6CO2 + 6H2O -> C6H12O6 + O2).

• Some reactions are reversible (e.g., 3H2 + N2 -> 2NH3).

• Chemical Equilibrium: The state where forward and reverse reactions occur at the same rate, resulting in no net change in concentration of reactants/products.