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

Electrolysis of Molten Sodium Chloride

Example: Molten sodium chloride:

• Cathode: 2H⁺(aq) + 2e^- → H₂(g) (hydrogen bubbles off)
• Anode: 2Cl^- → Cl₂(g) + 2e^- (chlorine gas produced)

Electrolysis of Aqueous Sodium Chloride

Aqueous solution of sodium chloride:

• At the cathode: Na⁺ and H⁺(aq) are present. H⁺(aq) is discharged because hydrogen is below sodium in the reactivity series. 2H⁺(aq) + 2e^- → H₂(g)
• At the anode: OH^- and Cl^- are present. Cl^- is discharged because it is in high concentration. 2Cl^-(aq) → Cl₂(g) + 2e^-

Positively charged ions move to the negative electrode during electrolysis. They receive electrons and are reduced.

Negatively charged ions move to the positive electrode during electrolysis. They lose electrons and are oxidized.

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What is an atom?

Atoms are the basic units of matter and the defining structure of elements.

What is an electron?

A subatomic particle with a charge of negative electricity.

What is the nucleus of an atom made of?

Is made up of protons and neutrons.

What is a proton?

Elemental particle of the nucleus of the atom and that has a positive electric charge.

What is a neutron?

A subatomic particle of about the same mass as a proton but without an electric charge.

Where is the mass of an atom concentrated?

In the nucleus most of 99.9% of the mass is concentrated here.

An atom is mostly empty space?

Yes.

What is the function of neutrons?

To allow protons to be together.

What surrounds the nucleus of an atom?

The nucleus is surrounded by electron clouds that produce... Continue reading "Understanding Atoms and Quantum Mechanics: A Comprehensive Guide" »

Chemistry Fundamentals

Arranging the Elements: The Periodic Table

• Organizing the elements according to their properties.
• Dmitri Mendeleev discovered a pattern to the elements in 1869.
• Periodic means “happening at regular intervals.”
• Mendeleev found that element properties follow a pattern that repeated every 7 elements.
• He found that elements yet to be found would fill the gaps. By 1886, all of the gaps had been filled.
• In 1914, Henry Moseley determined the number of protons. Elements were arranged by atomic number. The Periodic Law states that the repeating physical and chemical properties of elements change periodically with the element's atomic number.

Classifying Elements on the Periodic Table

• Metals: Found to the left of the zigzag line on

In the periodic table, elements are classified into metals, nonmetals, and metalloids. Metals are ductile, malleable, shiny, are good conductors for heat and electricity. All metals are solids at room temperature and pressure except, Mercury. Nonmetals exist as solids, liquids, or gases. A liquid non-metal at room temperature and pressure is Bromine.

2. The elements in the d-block in the periodic table have several characteristics in common.

(i) Give the electron configuration of N²⁺

1S2 2S2 2P3- 2= 1S2 2S2 2P1

(ii) Explain what is meant by a ligand and describe the type of bond formed between a ligand and a d-block element.

It is an atom or molecule with a lone pair of electrons that combine with a metal through coordinate covalent bonding. In transition... Continue reading "Chemistry Basics: Metals, Nonmetals, and Transition Elements" »

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

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" »