Chemistry

SEMESTER 2!

Acids vs bases

Acid: It’s a substance that can donate protons (H⁺ ions) and makes things taste sour, like lemons and vinegar.

Base: It’s a substance that can accept protons (H⁺ ions) and often has a slippery or soapy feel, like soap or baking soda.

pH Scale: We discovered that the pH scale helps us measure how acidic or basic a substance is, ranging from 0 to 14. Anything below 7 is an acid, and anything above 7 is a base. Neutral substances, like pure water, that sits right at 7.

The Mole and Avogadro's Number

We started out our new semester with a mole or if we're talking in more chemical terms, the unit of measurement used to describe the number of particles found within a substance. There are many examples of units of measurement such as a dozen eggs which means 12, a pair of shoes which means 2, or a ream of paper which means 500. All of which count numbers just like the mole. A mol of anything is the unit of measure for anything that contains 6.02 x 10^23 items, also referred to as Avogadro's number. We can use the mol to convert from one unit of measure to another.

Percent Composition: The percent by mass of each element in a compound.

Formula: mass of element/mass of compound x 100

Stoichiometry

Mr. Lin has been teaching the freshmen about stoichiometry! Its a big word, but has simple terms. Stoichiometry is the study of the quantities of reactants and products in chemical reactions. It helps us figure out how much of each substance we need to start with to create the desired products.

For example, in a reaction like the combustion of methane (natural gas), the stoichiometric calculations can tell us how much oxygen is needed to burn a specific amount of methane and how much carbon dioxide and water will be produced.

Why is stoichiometry so important? It’s crucial for things like:

Determining how much of a product you can expect from a reaction
Making sure chemical reactions are efficient and safe
Creating the perfect recipe in industries like pharmaceuticals, food production, and even space travel!

There are 3 types that we learned of: Mole to Mole, Mole to Mass, and Mass to Mass the order of these types going from the least number of steps needed to the most (example of mass to mass on the right).

Limiting Reactant

In chemistry, the reactant you run out of first is called the limiting reactant or limiting reagent. When you run out of a reactant, the reaction stops and no more product can be made. The limiting reactant determines how much product will be made, but it is not always the substance you have least of because it also depends on the ratio of how you are using that substance.

Percent Yield

Theoretical Yield :The maximum amount of product you should make based on stoichiometry calculations.

Actual Yield: The amount of product you actually make by doing the reaction in the lab. It is usually less than theoretical.

Heres a flow chart on how to calculate Mass-Mass

Example of limiting reactant

SEMESTER 1!

Atomic Theory and Atomic Structure

This was our first unit in chemistry. We mostly covered what we learned in eighth grade but we did brief over the topic of how the atom evolved into what it is today. Over history many people had different ideas about what the atom looked like and it's structure. People once thought there were no subatomic particles until John Thomson discovered electrons followed by Rutherford discovering protons, and James Chadwick discovering neutrons which eventually ended up leading to the current atomic model we know today and the structure behind it. Mr. Lin lead us through the history of the atom along with a quick refresher on what is contained in the atom.

Periodic Trends

Ionization Energy: Ionization energy is the amount of energy required to remove an electron from an atom or ion in its gas phase. In simpler terms, it's the energy needed to "push off" an electron from an atom. The higher the ionization energy, the harder it is to remove the electron.

Atomic Radius: Atomic radius is the size of an atom, measured from its nucleus to the outermost electron. The more electron shells an atom has, the larger it becomes. So, as you go down the periodic table, atoms get bigger. On the other hand, as you move from left to right across a period, atoms get smaller because more protons in the nucleus pull the electrons closer.

Electronegativity: Electronegavitiy is the ability of an atom to attract electrons in a chemical bond. The higher the electronegativity, the greater an atom's ability to attract electrons. Therefore as we go from right to left the electronegativity increases and as we go from top to bottom the electronegativity decreases because the attraction does.

Ionic Radius: Ionic Radius is essentially the same thing as atomic radius but it's the distance from the nucleus of the ion and the outermost shell of the ion. Going down a group causes the ionic radius to increase and across a period for the ionic radius to decrease.

Intermolecular and Intramolecular forces

Intramolecular forces are the strong forces that hold atoms together within a molecule, such as covalent, ionic, or metallic bonds. These forces determine a substance's chemical properties. Intermolecular forces, on the other hand, are weaker forces that act between molecules and influence physical properties like boiling point and solubility. Examples include London dispersion forces, dipole-dipole interactions, and hydrogen bonds. While intramolecular forces are responsible for the structure and stability of molecules, intermolecular forces affect how molecules interact with each other in different substances.

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