Chemical Bonds and Energy

Introduction to Chemical Bonds

• Chemical bonds are crucial in biology as they underlie the biochemical processes occurring within cells.

• These involve constant reactions, like cellular respiration and neurotransmitter activity, highlighting the chemical basis of life.

Atom Structure and Bonds

• Atoms consist of a nucleus (protons and neutrons) and electrons orbiting around it.

• Modern atomic model shows electrons exist in a cloud around the nucleus rather than fixed orbits.

• Electrons interact during the formation of chemical bonds.

Valence Electrons

• The outermost electrons (valence electrons) determine an atom's chemical properties.

• The octet rule states atoms are stable if they have eight valence electrons.

• Stability makes certain elements (e.g., noble gases like Neon and Argon) non-reactive.

Reactivity of Atoms

• Atoms like Sodium (Na) have a single valence electron, making them very reactive.

• Sodium reacts violently with water, which illustrates its instability.

• Chlorine (Cl) has seven valence electrons and is also very reactive, seeking another electron.

Formation of Ionic Bonds

• When sodium loses an electron to chlorine, it forms Na+ and Cl-, creating an ionic bond and resulting in stable sodium chloride (table salt).

• This bond formation occurs because together they achieve full valence electron shells.

Types of Chemical Bonds

Ionic Bonds

• Formed when one atom gives up an electron while another atom accepts it, creating charged ions that attract each other.

Covalent Bonds

• Formed when two atoms share one or more pairs of electrons.

• Example: Oxygen (O2) and Hydrogen (H2) are molecules formed by covalent bonds.

Polar Covalent Bonds

• Electrons are shared unequally, creating partial charges within the molecule.

• Water (H2O) is a polar molecule, with partial charges leading to hydrogen bonding.

Properties of Water

• Because of its polar nature, water has unique properties crucial for life, such as:

  • Cohesion (water molecules sticking together).

  • Adhesion (water molecules sticking to other surfaces).

  • High specific heat and surface tension.

Energy in Chemical Reactions

• Energy dynamics revolve around bond making and breaking.

Exergonic Reactions

• Reactions that release energy when bonds are broken; reactants have more potential energy than products.

• Examples include:

  • Burning wood or candle flames.

  • Cellular respiration, releasing energy from glucose.

Endergonic Reactions

• Reactions that require energy input to form products with higher potential energy than reactants.

• Photosynthesis is a prime example – the process absorbs energy from sunlight to create glucose.

Metabolism

• Metabolism encompasses all biochemical reactions that occur within an organism.

• It includes both anabolic (building) and catabolic (breaking down) pathways, enabling organisms to manage energy efficiently over time.