HLTH1004 W2 L2.2.2

Chemical Bonds

• Elements bond by sharing, gaining, or losing electrons in their outermost shells.

• The three primary types of chemical bonds:

  • Covalent Bonds: Sharing of electrons.

  • Ionic Bonds: Complete transfer of electrons.

  • Hydrogen Bonds: Weak attractions, where hydrogen is covalently bonded to either Nitrogen, Oxygen or Fluorine (H-NOF)

• Strongest to weakest bonds: Covalent (triple → double → single) → ionic → hydrogen

• Molecules: Groups of atoms held together by stable bonds.

• Compounds: Groups of molecules with more than one type of element.

Covalent Bonds

• Covalent bonding involves sharing of electrons between atoms.

• Types of covalent bonds based on shared electron pairs:

  • Single Covalent Bond: 1 pair shared.

  • Double Covalent Bond: 2 pairs shared.

  • Triple Covalent Bond: 3 pairs shared.

• Examples:

  • Hydrogen Molecule (H2): Two hydrogen atoms share one electron each.

  • Oxygen Molecule (O2): Two oxygen atoms share two electron pairs (double bond).

  • Carbon Dioxide (CO2): Carbon shares two pairs of electrons with each of the two oxygen atoms (double bonds).

  • Nitrogen Molecule (N2): Two nitrogen atoms share three pairs of electrons (triple bond).

• Covalent bonds can be polar or nonpolar:

  • Polar Covalent Bonds: Unequal sharing of electrons, leading to partial charges (e.g., water).

  • Nonpolar Covalent Bonds: Equal sharing of electrons, no overall charge (e.g., diatomic molecules of the same element).

Ionic Bonds

• Ionic bonding involves the complete transfer of electrons from one atom to another.

• Example: Sodium (Na) and Chloride (Cl) in table salt (NaCl).

  • Sodium (Na) has one electron in its outermost shell, while chlorine (Cl) has seven electrons in its outermost shell. Sodium can achieve a stable electron configuration (similar to a noble gas) by losing one electron, and chlorine can achieve stability by gaining one electron. Both atoms seek a more stable electron configuration by achieving a full outer electron shell (octet rule).

  • Sodium loses its one outer electron to become a positively charged ion (Na⁺). Chlorine gains this electron to become a negatively charged ion (Cl⁻).

    • Cation is positively charged, while Anion is negatively charged (mnemonic: "Cation", the “t” is positive ‘+’).

  • The positively charged sodium ion (Na⁺) and the negatively charged chloride ion (Cl⁻) are attracted to each other due to their opposite charges. This electrostatic attraction is called an ionic bond.

Water as a Polar Molecule

• Water (H₂O) consists of two hydrogen atoms and one oxygen atom.

• Oxygen attracts electrons more strongly than hydrogen, resulting in partial charges:

  • Oxygen: Slightly negative (δ-)

  • Hydrogen: Slightly positive (δ+)

• Creates hydrogen bonding between water molecules, leading to:

  • Surface tension

  • Cohesion and adhesion properties

• Hydrogen bonds are weaker compared to ionic and covalent bonds and can be broken with energy input.

States of Matter

• Matter exists in various states based on energy levels:

  • Gas: Highest energy state; atoms spread far apart.

  • Liquid: Intermediate energy state; atoms are closer together but can move freely.

  • Solid: Lowest energy state; atoms are tightly packed and vibrate in fixed positions.

• Transitioning between these states involves energy changes:

  • Cooling gases can form liquids; cooling liquids can form solids.

  • Some substances can bypass states (e.g., sublimation from solid to gas).

Summary

• Understanding ionic, covalent, and hydrogen bonds is key to grasping molecular and compound structures.

• Water's polarity allows it to engage in hydrogen bonding, which is essential for many biological and physical processes.