Chemistry Chapter 2 Overview

Introduction

• Chemicals are essential components of our bodies, other organisms, and the environment.
• Water is fundamental for life; it was the medium where life first evolved, and all organisms require it.
• Cells consist of approximately 75% water.

Elements, Atoms, and Compounds

• Organisms are made of elements that combine to form compounds.
• Matter occupies space and has mass, comprising chemical elements.
• An element cannot be broken down by ordinary chemical means; there are 92 naturally occurring elements.
• Compounds consist of two or more different elements in fixed ratios and are more common than pure elements.
• Sodium chloride (table salt) is a notable example, composed of equal parts sodium (Na) and chlorine (Cl).
• About 25 elements are essential for human life, with four elements—Oxygen, Carbon, Hydrogen, and Nitrogen—accounting for 96% of living organisms' mass.
• Trace elements are vital but needed in minute quantities; for example, iron is crucial for oxygen transport in the body.

Thermal Energy and Temperature

• Thermal energy relates to the random motion of atoms and molecules.
• Heat is the transfer of thermal energy from a warmer object to a cooler one.
• Temperature measures heat intensity, indicating average molecular speed in a substance.
• Heat absorption is necessary to break hydrogen bonds; heat is released when hydrogen bonds form.
• Raising water temperature requires breaking hydrogen bonds, which leads to significant heat absorption, while cooling releases heat as bonds form.

Water and Temperatures

• Earth's substantial water supply regulates temperatures, maintaining conditions conducive to life.
• Water's high resistance to temperature change stabilizes ocean temperatures, benefiting marine ecosystems.
• Evaporative cooling occurs when a substance evaporates, cooling the remaining liquid as energetic molecules escape.

Ice Floats

• Ice floats due to being less dense than liquid water.
• Water exists in gas, liquid, and solid states, with unique density qualities influenced by hydrogen bonding.
• When water freezes, stable hydrogen bonds result in a less densely packed structure than in its liquid state.

Hydrogen Bonds

• Hydrogen bonds are weak yet crucial for various chemical processes.
• Strong covalent bonds form the primary structure of cellular molecules, but functional cellular activities often rely on weaker bonds like hydrogen bonds.
• Water's polar nature, due to polar covalent bonds between hydrogen and oxygen, facilitates hydrogen bonding.
• Each water molecule can form up to four hydrogen bonds due to its structure, allowing significant interactions among water molecules.
• Chemical reactions involve making and breaking chemical bonds; for example, the reaction of hydrogen and oxygen to form water exemplifies a chemical reaction.