SE Unit 1 Topic 1 Notes- Hydrogen Bonding _ Structure of Water

Structure of Water and Hydrogen Bonding

Overview of Water Structure

• Water is a polar molecule, characterized by its molecular structure where one oxygen atom is bonded to two hydrogen atoms.

• The polarity leads to hydrogen bonding, which is crucial for many of water's unique properties.

Hydrogen Bonding

• Hydrogen bonds are weak attractions between a partially positive hydrogen atom in one molecule and a highly electronegative atom in another molecule, typically oxygen or nitrogen.

• These bonds are responsible for the cohesive and adhesive properties of water, which enable various biological functions.

Enduring Understandings and Learning Objectives

Course Content

• SYI-1 Living systems are organized hierarchically and interact at various levels.

• SYI-1.A Essential Knowledge:

  • SYI-1.A.1: The polarity and hydrogen bonding properties of water affect its functions in biological systems.

  • SYI-1.A.2: Living organisms depend heavily on the properties of water, such as its ability to dissolve substances and facilitate chemical reactions.

  • SYI-1.A.3: Hydrogen bonds result in water's cohesive, adhesive properties and surface tension.

Chemistry Basics

Matter

• Matter: Anything that occupies space and possesses mass (e.g., rocks, metals, gases).

• Elements: Substances that cannot be broken down further; there are 92 naturally occurring elements in nature.

• Compounds: Substances consisting of two or more different elements combined in fixed ratios (e.g., H2O, NaCl).

Essential Elements

• Of the 92 elements, only 20-25% are essential for life, with CHON (Carbon, Hydrogen, Oxygen, Nitrogen) making up 96% of living matter.

• Trace elements: Needed in very small quantities but are critical for biological functions.

Atomic Structure and Models

Atomic Number and Mass

• Atomic number refers to the number of protons in an atom.

• Atomic mass includes the total number of protons and neutrons, averaged across isotopes.

Bohr Model

• The Bohr model illustrates electrons orbiting around the nucleus in distinct energy levels.

• Each electron shell has a maximum capacity: 1st shell (2 electrons), 2nd shell (8 electrons), and 3rd shell (up to 18 electrons).

• Lithium is an example with 3 protons, 3 electrons, and 1 valence electron.

Chemical Bonding

• Chemical Bonds: Interactions that hold atoms together via shared or transferred electrons.

• Electronegativity: A measure of an atom’s ability to attract electrons; it varies in the periodic table.

Types of Bonds

Covalent Bonds

• Covalent Bonds: Formed by the sharing of electrons between atoms, can be single, double, or triple bonds.

  • Nonpolar covalent bonds: Electrons are shared equally.

  • Polar covalent bonds: Electrons are shared unequally, leading to partial charges (e.g., water, H2O).

Ionic Bonds

• Ionic Bonds: Formed through the transfer of electrons which creates charged ions (cations and anions), establishing electrostatic attractions (e.g., NaCl).

Properties of Water

Cohesion

• Water molecules exhibit cohesion due to hydrogen bonding, allowing them to stick together, leading to surface tension which supports structures like water striders.

• Cohesion aids in the movement of water and nutrients against gravity in plants.

Adhesion

• The attraction of water molecules to other substances (adhesion) helps water cling to plant cell walls, resisting gravity.

Capillary Action

• Capillary Action: The movement of water upward in plants due to cohesion and adhesion, essential for nutrient transport.

Temperature Control

• High Specific Heat: Water’s ability to absorb and release heat helps moderate environmental temperatures and stabilizes marine environments.

• Evaporative Cooling: Water's high heat of vaporization helps regulate temperature for ecosystems and organisms.

Ice Density

• When water freezes, it expands and becomes less dense, allowing ice to float and insulate aquatic life beneath it.

Solvent Properties

• Water, due to its polarity, acts as a versatile solvent, dissolving various substances and facilitating biochemical reactions.

• Water can dissolve ionic compounds by surrounding charged ions, allowing substances to mix homogeneously.