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

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

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" »

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

Fundamental Chemistry Definitions

Chemical Bond

The force that holds two or more atoms together to form a compound.

Litmus Paper

Paper strips containing litmus, available in both blue and red, used to indicate pH.

Ionic Compound

A compound formed from oppositely charged ions.

Hydronium Ions

Ions (H₃O⁺) that form when a hydrogen ion (H⁺) separates from an acid and bonds with a water molecule (H₂O).

Hydroxide Ion

Ions (OH⁻) that form when a base dissolves in water and dissociates.

Brittleness

The tendency of ionic compounds to be brittle solids at room temperature, causing them to break apart easily when struck.

Corrosive

A property of a substance that causes destruction or damage upon contact with other materials.

Melting Point

The temperature at... Continue reading "Understanding Core Chemistry Terms" »

• Isotopes

  • Same elements with different numbers of neutrons

• Ions

  • Same element with an unequal number of protons and electrons

• Electric Fields

  Things with charge (protons and electrons) generate electric fields (E) (Likewise, electric fields can affect things with charge)

• Energy and Matter

  When atoms or molecules “happen across” energy, [usually] 1 of 2 things can happen: 1) they wiggle-jiggle more [we classify the amount of “wiggling-jiggling” by the quantity of temperature] 2) the energy, if it is a) in the form of a special type of electromagnetic field and b) of a specific frequency, can be absorbed

  λ∙f = c

  λ = wavelength of the wave [m]

  f = frequency of the wave [Hertz, Hz=1/s]

  c = speed of light = 3∙108 m/s

  Electromagnetic Waves

Dalton's Atomic Theory

John Dalton proposed that elements were made up of little solid spheres without internal structure. Atoms of the same element were equal. Atoms combine, forming compounds. Depending on the ratio, we can have different compounds.

J.J. Thomson

First model of the atom (1904). He discovered/proved the existence of tiny, negatively charged particles: electrons.

Rutherford's Model of the Atom

Gold foil experiment, Ernest Rutherford (1911). Alpha particles are tiny, positively charged particles much smaller than an atom. An atom is mostly empty space. Some particles will bounce back, and some others will pass but in a different way. The nucleus is something dense and positively charged.

Thomson's Atomic Model

In 1904, Thomson's atomic... Continue reading "Dalton's Atomic Theory and the Evolution of Atomic Models" »

Chemical Reactions

occurring at low temperatures are
                _______low______ than reaction rates of chemical reactions occurring at high
temperatures.

40. Increasing pressure causes gas particles to             ______collide_______________. This
                ________increases______________ the reaction rate of a chemical reaction.

41. All reactions require    ___activation energy___________ for chemical bonds to begin breaking.

Exercise 3 – Analyzing the Financial Impact of Price and Volume Changes on Apple iPhones

Apple iPhone Sales and Manufacturing Costs

In 2014, Apple sold approximately 150,000,000 iPhones at a price of $640 per unit. The company's average manufacturing cost per iPhone is detailed in Table 1.

Table 2 outlines Apple's fixed costs associated with its iPhone business.