w1 Chemical Level of Organisation

  • Matter

    • Definition: Anything occupying space; possesses mass.

    • States of matter: solid, liquid, gas.

  • Elements

    • Unique substances made of atoms.

    • Cannot decompose further by chemical means.

    • Human body contains approximately 26 elements.

  • Periodic Table

    • Elements arranged by atomic numbers; symbols represent elements (

    • Example: Carbon (C), Oxygen (O)).

  • Atoms

    • Smallest units of elements retaining element properties.

    • Composed of three subatomic particles:

    • Protons: Positive charge, located in the nucleus, mass ~1 amu.

    • Neutrons: Neutral charge, located in the nucleus, mass ~1 amu.

    • Electrons: Negative charge, orbit nucleus, negligible mass.

  • Atomic Number

    • Unique to each element; defined as the number of protons (e.g. Oxygen has 8 protons).

  • Isotopes

    • Different atomic forms of the same element, differing in neutron count (e.g. Deuterium (2H), Tritium (3H)).

    • Some isotopes are radioactive and used in medical applications.

  • Atomic Stability and Reactivity

    • Stable: Complete outer electron shell; unreactive.

    • Unstable and Reactive: Incomplete shell; reacts to achieve stability, forming ions.

  • Ionic Bonds

    • Formed by attraction between cations (positively charged) and anions (negatively charged) through electron transfer.

  • Electrolytes

    • Compounds that dissociate into ions in solution; essential for muscle and nerve functions. (e.g. NaCl dissociates into Na+ and Cl-).

  • Covalent Bonds

    • Atoms share electrons to achieve stability.

    • Example: Water (H2O) is formed via covalent bonds.

  • Polar Covalent Bonds

    • Asymmetric sharing of electrons creates regions of partial positive and negative charge (e.g. water molecules).

  • Hydrogen Bonds

    • Weak attractions between the positive charge of hydrogen atoms and negative charges of adjacent atoms.

  • Molecular Weight

    • Sum of the atomic weights of all constituent atoms in a molecule (e.g. Sodium Chloride: NaCl).

  • Concentration Measurements

    • Molarity: measures the amount of substance in relation to the volume of solvent.

    • 1 mole of substance corresponds to its molecular weight in grams per liter (e.g. 58 g of NaCl corresponds to 1 mol/L).

  • Summary Points

    • Atoms are fundamental; electron patterns influence reactivity.

    • Chemical bonds enable life through the formation of various compounds and molecules.