Atoms, Molecular Bonds, and Properties of Water: Study Guide

Study Guide - Smart Notes

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Atoms are the basic units of matter, consisting of three main subatomic particles:

Protons: Positively charged particles located in the nucleus.
Neutrons: Neutral particles also found in the nucleus.
Electrons: Negatively charged particles that orbit the nucleus in electron shells.

Atomic Number: The number of protons in an atom's nucleus; determines the element's identity.
Atomic Mass: The sum of protons and neutrons in the nucleus; often expressed in atomic mass units (amu).
Example: Carbon has an atomic number of 6 and an atomic mass of approximately 12.

Electrons in shells farther from the nucleus (higher shells) have higher energy than those in shells closer to the nucleus.
Example: An electron in the third shell has more energy than one in the first shell.

Molecular bonds are the forces that hold atoms together in molecules. The main types are:

Covalent Bonds: Electrons are shared between atoms. These bonds can be very strong.
- Nonpolar Covalent Bonds: Electrons are shared equally.
- Polar Covalent Bonds: Electrons are shared unequally, resulting in a molecule with partial positive and negative charges (a dipole).
Ionic Bonds: Electrons are transferred from one atom to another, resulting in oppositely charged ions that attract each other.
Hydrogen Bonds: Weak attractions between a slightly positive hydrogen atom in one molecule and a slightly negative atom (often oxygen or nitrogen) in another molecule.

Examples and Strengths

Chemical equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction.
Reactants: Substances that start a chemical reaction.
Products: Substances formed as a result of the reaction.
At equilibrium, concentrations of reactants and products remain constant (but not necessarily equal).

The structure of a molecule (its shape and arrangement of atoms) determines its function in biological systems.
Example: The double helix structure of DNA allows it to store genetic information efficiently.

Hydrogen bonds form between the slightly positive hydrogen atom of one water molecule and the slightly negative oxygen atom of another.
This gives water many of its unique properties.

Water is a polar molecule because of the unequal sharing of electrons between oxygen and hydrogen atoms.
This polarity allows water molecules to form hydrogen bonds with each other.

Cohesion: The attraction between water molecules due to hydrogen bonding.
Adhesion: The attraction between water molecules and other substances.
These properties contribute to phenomena such as surface tension and capillary action.

A calorie is a unit of energy; specifically, it is the amount of heat needed to raise the temperature of 1 gram of water by 1°C.
The "calorie" in food is actually a kilocalorie (kcal), or 1,000 calories.

Water has a high specific heat, high heat of vaporization, and is less dense as a solid than as a liquid.
These properties are essential for life, helping to regulate temperature and allowing ice to float, which insulates aquatic environments.
Example: Water's high specific heat helps stabilize Earth's climate.

Water is known as the "universal solvent" because it can dissolve many substances, especially ionic and polar compounds.
This property is crucial for biological processes, such as nutrient transport and chemical reactions in cells.

A buffer is a substance that minimizes changes in pH by accepting or donating hydrogen ions (H+).
Buffers are important in maintaining stable pH in biological systems.

Rising carbon dioxide levels increase the acidity of ocean water, a process known as ocean acidification.
In scientific studies, the independent variable is the factor that is changed (e.g., CO2 levels), and the dependent variable is what is measured (e.g., pH of ocean water).
Hypotheses are supported or falsified based on experimental results.

Molality (m) is a measure of concentration, defined as the number of moles of solute per kilogram of solvent.
Formula: