Chemistry

Properties of Atoms

Atoms

The basic building blocks of matter, composed of three subatomic particles: protons, neutrons, and electrons.
- Structure:
  - Nucleus: Central core containing protons (positively charged) and neutrons (neutral).
  - Electron Cloud: Surrounds the nucleus and holds electrons (negatively charged), arranged in shells or energy levels.
  - Energy Levels: Electrons further from the nucleus have higher energy, and moving an electron away requires energy due to the attraction between negative electrons and the positive nucleus.

Key Concepts

Isotopes: Variants of an element with different numbers of neutrons.
Atomic Mass: Calculated as the total number of protons and neutrons in the nucleus.
Atomic Number: Defined by the number of protons in an atom.
Ions: Atoms with an electrical charge.
- Cations: Positively charged ions.
- Anions: Negatively charged ions.
Valence Electrons: Electrons in the outermost shell; atoms are most stable when their valence shell is full.
- Electron Gain: Leads to a negative charge.
- Electron Loss: Leads to a positive charge.

Electron Organization

Shell: The primary pathway electrons follow around the nucleus.
Subshell: Divisions within a shell.
Orbital: Specific regions in subshells where electrons are likely to be found (e.g., s, p, d, f).
Electron Capacity Formula: Maximum electrons in an energy level = 2n² (where n is the energy level number). For example, the 4th energy level can hold 32 electrons (2 × 4² = 32).

Types of Chemical Bonds

Covalent Bonds

Formed when two atoms share electrons equally to achieve stability.

Ionic Bonds

Created when electrons are transferred from one atom to another, resulting in one atom predominantly holding the electrons to achieve stability.

Physical Properties of Matter

Physical Properties

Characteristics that can alter the state of a substance without changing its identity.
- Example: Steam produced from boiling water retains the same molecular structure as liquid water.

Key Measures

Mass: Reflects the number of molecules in a substance.
Volume: Indicates the amount of space occupied by the molecules in a substance.
Density: The ratio of mass to volume, describing how compact a substance is.

States of Matter

Matter exists in four distinct phases (solid, liquid, gas, plasma).
- Phase Determinants:
  - Temperature: Raising temperature increases molecular motion, pushing particles apart.
  - Pressure: Increasing pressure brings particles closer together.

Kinetic Molecular Theory

Describes how molecular motion varies with heat energy; motion increases when heat is added and decreases when heat is removed.

Water

Polarity: Water molecules have a negatively charged oxygen side and positively charged hydrogen sides.
Cohesion: Water molecules cling to one another, creating surface tension.
Adhesion: Water molecules adhere to other particles or surfaces.
Universal Solvent: Water dissolves many substances, making it essential in various chemical processes.

Solvents and Solutes

Definitions

Solute: The substance being dissolved.
Solvent: The medium dissolving the solute.
Solution: A homogeneous mixture formed when solutes dissolve in solvents.

Dilution

Involves adding more solvent to decrease the concentration of solute.

Concentration Measures

Molarity (mol/L): Moles of solute per liter of solution; depends on temperature.
Mole Fraction (mol/mol): Moles of solute divided by total moles in the mixture.
Molality (mol/kg): Moles of solute per kilogram of solvent.
Mass Percentage (g/g): Ratio of solute mass to solution mass.
Parts Per Thousand (PPT): Grams of solute per kilogram of solution.
Parts Per Million (PPM): Milligrams of solute per kilogram of solution.
Parts Per Billion (PPB): Micrograms of solute per kilogram of solution.

Diffusion and Osmosis

Diffusion: Movement of substances from areas of higher concentration to lower concentration (e.g., gas exchange in lung capillaries).
Osmosis: Water movement across a membrane, flowing from higher to lower water concentration.
Active Transport: Energy is required to move substances from areas of lower to higher concentration.

Chemical Reactions

Catalysts (enzymes): reduce the activation energy needed for a reaction, accelerate the process, and can be utilized repeatedly.

Synthesis: the process of combining components to form a more complex substance or structure.

A + B >- AB

Decomposition: a chemical reaction in which a compound acts as the reactant and is broken down into simpler products.

AB – > A + B

Single replacement: a reaction where one element within a compound is replaced by a different element, resulting in the formation of a new compound and a separate element as the products.

AB + C >- AC + B

Double replacement: a reaction in which two compounds swap ions, resulting in the creation of two entirely new compounds.

AB + CD – > AC + BD

Combustion: a process where a fuel combines with oxygen gas, producing carbon dioxide and water as the end products.

C× + Oy – > CO2 + H20

Balancing Chemical Reactions

Tally the number of atoms for each element on both sides of the equation.
Apply the smallest possible coefficient to equalize the number of atoms for each element on both sides (consider atoms grouped in compounds).
The equation is now balanced.

Moles

One mole corresponds to the atomic mass of a substance in grams. For example, carbon has an atomic mass of 12 g, so 12 g of carbon equals one mole.
The number of moles for a substance can be determined using the atomic masses listed in the periodic table.
- For compounds, the atomic masses of individual elements are summed to calculate the total mass.

What is the mass in grams for 2 moles of NaCl?

Acid and Bases

pH: A scale that quantifies the concentration of hydrogen ions in a solution, ranging from 0 to 14.
Acids (hydrogen ion donors): Typically have a sour taste, a pH below 7, and a higher concentration of hydrogen ions than hydroxide ions.
- Introducing an acid to a solution decreases its pH.
Bases (hydrogen ion acceptors): Generally have a bitter taste, a pH above 7, and a higher concentration of hydroxide ions than hydrogen ions.
- Adding a base to a solution increases its pH.
Neutral: A solution with a pH of exactly 7, indicating it is neither acidic nor basic.
Buffer: A solution that stabilizes pH by minimizing shifts when acids or bases are introduced. Buffers help maintain pH balance in biological systems.
- Buffers absorb excess H+ or OH- ions to prevent significant pH changes.
pOH: A measure of hydroxide ion concentration in a solution. It is inversely related to pH— as pH increases, pOH decreases.
- Formula: pH + pOH = 14
- pH = -log[H+]
- pOH = -log[OH-]

Neutralization

Water formation from hydrogen and hydroxide ions:

When an acid reacts with a base, the hydrogen ions (H+) from the acid bond with the hydroxide ions (OH-) from the base, resulting in the formation of water.
If the quantities of acid and base are equal, the mixture reaches a neutral state.

Scientific Reasoning

Frequently used measurement prefixes:

The metric system is employed for measuring and recording data.
Measurement tools:

Length: ruler, meterstick
Solid volume: determined by multiplying length, width, and height
Liquid volume: measured with a volumetric flask, pipette, or graduated cylinder
- Liquids create a meniscus: a curve at the liquid’s surface due to the container’s walls.
- Concave: upward curve; Convex: downward curve
- To measure liquid, read the value at the line level with the meniscus’ center.

Independent variable: the factor that is intentionally altered or adjusted in an experiment, typically represented on the X-axis of a graph.
Dependent variable: the outcome or result that is observed and measured after the independent variable is modified, usually depicted on the Y-axis of a graph.
Controlled variables: all the factors that are kept constant and unchanging to ensure the experiment’s accuracy and validity.