Hoja de repaso: Fundamentals of Chemistry

📋 Course Outline

1. Periodic table and atomic structure
2. Substances, formulas and naming
3. Chemical bonds and structures
4. Chemical reaction laws and energy

📖 1. Periodic table and atomic structure

🔑 Key Concepts & Definitions

• Neutrons : Neutrons are subatomic particles with no electric charge found in an atom’s nucleus.
• Protons : Protons are positively charged particles in an atom’s nucleus that determine the atomic number.
• Valence electrons : Valence electrons are the electrons in an atom’s outermost shell that largely determine chemical behavior.
• Absolute atomic mass : Absolute atomic mass $A$ is the total count of protons plus neutrons in an atom.
• Relative atomic mass : Relative atomic mass is the atom’s average mass compared to $^{12}\mathrm{C}$ on the periodic table scale.

📝 Essential Points

• You read an element’s atomic number $Z$, mass number $A$, and electronegativity value ENW from the periodic table (PSE).
• From $Z$ and/or $A$ and/or ENW you can locate the matching element on the PSE.
• You determine the number of valence electrons and the outer shell from the element’s position (group/period) in the PSE.
• From $Z$ and $A$ you can write the number of protons, neutrons, and electrons for a neutral atom.
• You classify an element from the PSE as metal, non-metal, or noble gas and you name its group and period.

📖 2. Substances, formulas and naming

🔑 Key Concepts & Definitions

• Simple substance : A simple substance is a substance made of only one chemical element.
• Compound substance : A compound substance is a substance made from more than one chemical element.
• Brute formula : A brute formula shows which elements are present in a substance and how many atoms of each are in one unit.
• Systematic naming : Systematic naming is a structured name built from the brute formula using prefixes for the atom counts.
• Trivial naming : Trivial naming is a conventional short name for a substance that does not follow the systematic prefix scheme.

📝 Essential Points

• You classify a given substance as a simple substance or a compound substance.
• You label a reaction as analysis when one substance splits into multiple products, and as synthesis when multiple substances form one product.
• You can write the brute formula from a given systematic name or trivial name.
• You can write the systematic name from a given brute formula or trivial name.
• You can convert between brute formula and names by using Greek counting prefixes like mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, and octa-.
• You can determine how many atoms of a specified element are present in one or more described molecules.

📖 3. Chemical bonds and structures

🔑 Key Concepts & Definitions

• Ion bond : An ion bond is a bond formed by electron transfer that creates positively and negatively charged ions attracting each other.
• Covalent bond : A covalent bond is a bond formed by sharing electron pairs between atoms.
• Polar covalent bond : A polar covalent bond is a covalent bond with unequal electron sharing due to a difference in electronegativity.
• Apolar covalent bond : An apolar covalent bond is a covalent bond with equal electron sharing and (effectively) no net polarity.
• Structure formula : A structure formula shows how atoms are connected in a covalent compound using lines for bonds.

📝 Essential Points

• You identify a bond as ion bond, covalent bond, or metallic bond from the context provided in the question.
• You determine the type of covalent bond as apolar or polar and can draw its structure formula.
• You compute the electronegativity difference (ENW difference) for an indicated bond when needed to classify polarity.
• For an ion bond you write the electron transfer, form the correct ions, and state the formula unit made from them.
• For covalent compounds you draw the structure formula and for metallic bonding you list the ions present in the metal bonding description.

📖 4. Chemical reaction laws and energy

🔑 Key Concepts & Definitions

• Law of conservation of mass (Lavoisier) : The law of conservation of mass states that the total mass stays constant during a chemical reaction.
• Law of conservation of atoms : The law of conservation of atoms states that atoms are neither created nor destroyed in a reaction.
• Endo-energetic reaction : An endo-energetic reaction absorbs energy from its surroundings.
• Exo-energetic reaction : An exo-energetic reaction releases energy to its surroundings.
• Reaction equation : A reaction equation (reactievergelijking) represents reactants and reaction products using correct chemical formulas.

📝 Essential Points

• You apply Lavoisier’s law to check that the total mass before equals the total mass after the reaction.
• You apply the atom conservation law to ensure the reaction equation has the same number of each type of atom on both sides.
• You apply the energy conservation idea to decide whether a reaction is endo-energetic or exo-energetic.
• You classify a given reaction example as exo-energetic or endo-energetic based on whether energy is released or absorbed.
• You can give examples of both exo-energetic and endo-energetic reactions.

⚠️ Common Pitfalls & Confusions

1. Mixing up $Z$ and $A$: $Z$ gives protons, while $A$ equals protons plus neutrons.
2. Assuming valence electrons can be found from atomic number only rather than from the element’s position in the PSE.
3. Confusing ENW with the electronegativity difference used to decide polar vs apolar covalent bonding.
4. Switching labels of analysis and synthesis reactions: analysis splits, synthesis forms.
5. Forgetting that in ion bonds you must form ions first (with charge) before writing the formula unit.
6. Thinking simple/compound substance classification depends on physical state instead of on the number of elements present.

✅ Exam Checklist

1. Read $Z$, $A$, and ENW of an element from the PSE.
2. Use $Z$ and/or $A$ and/or ENW to find the correct element on the PSE.
3. Determine the number of valence electrons and the outer shell from an element’s group and period.
4. Calculate and write the numbers of protons, neutrons, and electrons for an atom using $Z$ and $A$.
5. State an element’s group, period, and metal/non-metal/noble gas classification from the PSE.
6. Write the correct ion of an element in an ion bond and name it as anion or cation.
7. Name a substance as simple or compound and use the correct brute formula.
8. Identify analysis vs synthesis for a given reaction description.
9. Convert between brute formula and systematic/trivial names.
10. Determine the number of atoms of an element in one or more given molecules.
11. Identify whether a bond is ion, covalent, or metallic and state the corresponding formula/bond representation.
12. Use electronegativity information to classify covalent bonds as polar or apolar and draw a structure formula.
13. Apply conservation of mass, conservation of atoms, and energy to reaction questions.
14. Classify reactions as endo-energetic or exo-energetic and give examples of both.