Chemistry Lecture Notes Review

Chemistry Basics

Chemistry is defined as the study of chemicals, specifically atoms and molecules.

Atoms are the basic units of chemistry; they are extremely small, fundamental objects that make up all matter.
Atoms are composed of three types of particles:
- Protons: Positively charged particles.
- Neutrons: Neutrally charged particles.
  - Both protons and neutrons are located in the nucleus, which is the central part of the atom.
- Electrons: Negatively charged particles that orbit the nucleus.

Elements are different types of atoms.
They are distinguished from one another based on the specific number of protons found within the atom's nucleus.
Elements are denoted using a one or two-letter symbol.
All known elements are listed on the periodic table.
Examples:
- Any atom with 19 protons is considered Potassium (K).
- Any atom with exactly 13 protons is Aluminum (Al).

Ions are chemicals (atoms or molecules) that have an unequal number of protons and electrons, resulting in a net electrical charge.
They are referred to as "charged chemicals".
The charge of an ion is indicated by a positive or negative number written in superscript above the elemental symbol.
- Cations: Positively charged chemicals. They have more protons than electrons (or fewer electrons than protons).
  - Example: Al^{3+} indicates an aluminum ion with 3 more protons than electrons.
- Anions: Negatively charged chemicals. They have more electrons than protons (or fewer protons than electrons).
  - Example: N^{3-} indicates a nitrogen ion with a -3 charge, meaning it has 3 more electrons than protons. An atom of nitrogen normally has 7 protons, so N^{3-} has 10 electrons.
  - Example: O^{2-} indicates an oxygen ion with a -2 charge, meaning it has 2 more electrons than protons. An atom of oxygen normally has 8 protons, so O^{2-} has 10 electrons.

Molecules are chemicals formed when two or more atoms are chemically bonded together.
They are denoted using elemental symbols written next to each other.
Numbers written in subscript indicate the number of each atom of the element to their left.
Examples:
- H_{2}O: A water molecule, composed of 2 Hydrogen atoms and 1 Oxygen atom, for a total of 3 atoms.
- H{2}O{2}: A hydrogen peroxide molecule, composed of 2 Hydrogen atoms and 2 Oxygen atoms, for a total of 4 atoms.
- O^{2+}: Represents a charged molecule with 1 more electron than protons (likely a typo in the original for O^{2+} vs O^{+} given the example of 8 protons + 1 electron making it O^{-} for 8 protons and 9 electrons, or 7 protons and 8 electrons for O^{+}). Assuming the intent from the image was a charged species with an imbalance.

Chemical bonds are the forces or attractions that hold molecules together.
There are four types of molecules, but two common types of chemical bonds are discussed:

Ionic bonds are formed between a cation (positively charged ion) and an anion (negatively charged ion).
When a cation and an anion come within close proximity, their opposite charges attract each other, causing them to stick together and form a molecule held by an ionic bond.
Examples:
- Na^{+} (sodium cation) + Cl^{-}(chloride anion) $\rightarrow$ NaCl (sodium chloride molecule, table salt).
- Na^{+} (sodium cation) + OH^{-}(hydroxide anion) $\rightarrow$ NaOH (sodium hydroxide molecule, lye).

Covalent bonds form when neighboring atoms share electrons.
These bonds are established as electrons orbit around neighboring atoms, leading to shared electron density that holds the atoms together.
Examples:
- N_{2} (nitrogen molecule): Formed by two nitrogen atoms sharing electrons. This is an example of a nonpolar covalent bond.
- H_{2}O (water molecule): Formed by hydrogen and oxygen atoms sharing electrons. This is an example of a polar covalent bond.
Two types of covalent bonds exist:
- Nonpolar Covalent Bonds: Occur when electrons are shared equally between two neighboring atoms. The electrons spend equal amounts of time orbiting both atoms.
- Polar Covalent Bonds: Occur when there is an unequal sharing of electrons between neighboring atoms. Electrons spend more time orbiting one atom than the other, leading to a partial negative charge on the atom attracting more electrons and a partial positive charge on the other atom.

A compound is a molecule made up of two or more different types of elements.
Examples:
- H_{2}O (water)
- NaCl (sodium chloride)

A chemical reaction involves the formation, breakdown, or rearrangement of chemical bonds and/or molecules.
An arrow between chemical names or formulas indicates that a reaction is occurring.
Reactants: Chemicals located to the left of the arrow.
Products: Chemicals located to the right of the arrow.
A plus sign (+) between two chemicals (reactants or products) means that the chemicals are separate.
Examples:
- A + B $\rightarrow$ AB (A and B are reactants, AB is the product).
- H{2} + O $\rightarrow$ H{2}O (Hydrogen and Oxygen are reactants, Water is the product).

Mixtures are created when two or more chemicals are present and mixed together.
There are two basic types of mixtures:
- Heterogeneous Mixture: Occurs when components or chemicals are distributed unequally within the mixture.
  - Example 1: Soil, where different components like sand, clay, and organic matter are not uniformly distributed.
  - Example 2: Salt and water where the salt has not fully dissolved or clumped unevenly.

Molecules containing one or more covalent bonds are generally able to dissolve in water.
Molecules made up only of non-covalent interactions (the transcript seems to indicate 'non covalent won't dissolve', this phrasing is a bit ambiguous, but generally polar covalent bonds are necessary for water solubility to form hydrogen bonds, while purely nonpolar covalent molecules like oils do not dissolve).
Molecules containing ionic bonds are commonly known as "salts". When mixed with water (H_{2}O), molecules with ionic bonds will typically dissolve.