Notes, summaries, assignments, exams, and problems for Chemistry

Foundations of Atomic Theory

Early Atomic Ideas: Democritus to Dalton

The concept of the atom has evolved significantly over centuries. Ancient Greek philosopher Democritus speculated that matter was composed of elementary, indivisible particles he called atoms.

Centuries later, John Dalton proposed the first modern atomic theory, laying the groundwork for modern chemistry. His postulates included:

• All matter is made of atoms.
• Atoms are indivisible and indestructible.
• All atoms of a given element are identical in mass and properties.
• Compounds are formed by a combination of two or more different kinds of atoms.
• A chemical reaction is a rearrangement of atoms.
• Atoms can be neither created nor destroyed.

Discovery of the Electron: J.J. Thomson

J.J. Thomson'

Electricity and Atoms

Electricity is an electric charge. But there is much more behind than the simple statement:

• Where do the charges come from?
• How do we move them? Where do they move?
• How does an electric charge cause mechanical movement or invent things?

Atoms and Charge

To understand it we start with atoms, one of the basic blocks of life and matter. An atom is three different particles: electrons, protons and neutrons. Each atom has a central nucleus, where protons and neutrons are attached. Around the nucleus there is a group of electrons in orbit. The number defines which chemical element the atom represents. This set is called the atom's atomic number. Electrons are the operation of electricity In its most stable and balanced state, an atom... Continue reading "Understanding Electricity: Atoms, Charge, and Flow" »

• Metal + nonmetal = ionic bond

•  Nonmetal + nonmetal = covalent bond  

•  Metal + metal = metallic bond

• Electron filling pattern: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f

• Physical Changes

  • Do not create a new substance.

• Chemical Changes - Do produce new substances.

•  Ions - Atoms can gain or lose electrons to form ions (atoms with a charge. 

• • Anion - Atom with a negative charge. 

• • Cation - Atom with a positive charge.
  

• quantitative= number/amount, qualitative= observation of physical change
  

• alkali metals the column of elements from lithium to francium.
  

• Alkaline earths the column of elements from beryllium to radium.
  

• Halogens the column of elements from fluorine to astatine.
  

• The Periodic Law states that the physical and

Ionic Bonds

Ionic bonding is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions. Ionic bonds form when a metal and a non-metal exchange electrons. Positive ions are called cations and negative ions are called anions.

Ionic Substances

All ionic compounds form crystals that consist of lattices of positive and negative ions packed together in a regular way. The lattice is held together by the strong electrostatic attractions between the ions. Ionic compounds form crystals because the ions are arranged in a regular and repeated pattern, known as a Giant Ionic Lattice.

Properties of Ionic Substances

• High Melting and Boiling Points: Ionic bonds are very strong. Significant energy is required to break

Understanding Physical Sciences

Branches of Physical Science

• Chemistry: The study of the composition, structure, and properties of substances. It is the science that investigates the composition, structure, and properties of matter.
• Physics: The science that deals with matter, energy, motion, and force.
• Earth Science: The study of Earth and its various components.

Why Chemistry is a Physical Science

Chemistry is considered a physical science because it studies what exists around the world, such as atoms and molecules. Physical sciences primarily focus on non-living things.

Fundamental Concepts of Matter

Basic Definitions

• Mass: A measure of the amount of matter in an object.
• Matter: Anything that has mass and takes up space.
• Atom: The smallest unit of

Understanding Chromatography

Chromatography is used in column chromatography. The y-axis represents the intensity of the signal provided by the detector, and the x-axis represents time. Peaks can give us sample information, both qualitative and quantitative. Detectors are usually connected to computers that provide the different peak parameters (height, amplitude, etc.), relating them to the concentration. The position of the peak (time) provides qualitative information, and the areas or heights of the peak provide quantitative information.

The retention time, tR, is the time it takes for a component to come out from the injection of the sample into the column up to the middle of its peak. The areas of the peaks are proportional to the concentration... Continue reading "Understanding Chromatography: Principles, Phases, and Methodology" »

Core Concepts in Organic Chemistry

Nucleophilic Substitution Reactions

SN1 Reaction: Unimolecular Substitution

SN1 stands for Substitution Nucleophilic Unimolecular reaction. It proceeds in two steps:

1. Slow Step: Dissociation of the substrate to form a carbocation intermediate.
2. Fast Step: The carbocation combines with the attacking nucleophile.

Characteristics of SN1 reactions:

• More stable carbocation leads to a faster reaction.
• Favored by polar solvents.
• Mostly given by tertiary alkyl halides.
• Occurs with racemization.
• Follows 1st-order kinetics: Rate = k[R-X].

SN2 Reaction: Bimolecular Substitution

SN2 stands for Substitution Nucleophilic Bimolecular reaction. It proceeds in a single step, which is the rate-determining step.

Characteristics of SN2 reactions:... Continue reading "Essential Concepts in Organic Chemistry: Reactions and Mechanisms" »

-Explain What- A pure substance is a sample of matter with both definite and constant Composition with distinct chemical properties. Every pure element is a Substance. Every pure compound is a substance.Ex: water.

- What is- . A solution is a combination of two things, but it is well mixed down to the Molecular level and stable.Ex:Salt water .A heterogeneous mixture on the other Hand will settle.Ex:Chocolate milk.

 -what does- The chemical formula of a compound Indicates what the compound is made of. For example H2O has two hydrogen and One oxygen.

-Explain How- Atoms of different elements have different numbers of protons and neutrons In their nucleus. More importantly, they have different numbers of electrons Around the nucleus. It is the interaction... Continue reading "Coh3 chemical name" »

Chromium: A Versatile and Essential Element

Chromium is a useful, very hard, crystalline, steel-gray metal, discovered by Louis Vauquelin in 1797 while working with a material known as Siberian red lead (crocoite). While you might think of highly polished chrome electroplating, purified chromium metal is grayish in color, but still very bright and lustrous. The attribute that makes electroplating perfect is that it's really corrosion resistant. It won't easily rust.

Chromium's symbol is: Cr. Its atomic number is 24. It is located in group 6, and period 4.

The name of the element is derived from the Greek word, chrōma, meaning color, because many chromium compounds are intensely colored.

Applications of Chromium

Chromium plating can be used to give... Continue reading "Chromium: Properties, Uses, and Benefits of Element 24" »

Understanding Substance Separation Methods

Separating mixtures is a fundamental process in chemistry and daily life. These techniques leverage differences in physical or chemical properties of the components. Below are common methods for separating substances, categorized by the primary property exploited.

Separation Based on Physical Properties

Magnetization

• Principle: Magnetic properties.
• Process: Magnetic materials are attracted to a magnet, separating them from non-magnetic substances.
• Example: Separating iron filings from sand.

Sieving

• Principle: Particle size.
• Process: Larger solid substances are retained by the sieve, while smaller ones pass through.
• Example: Separating stones from sand.

Filtration

• Principle: Particle size.
• Process: A solid substance