Chemistry Quiz: Molecular Structure and Classification

Study Notes

An atom is the fundamental unit of an element.
Atoms cannot be broken down by chemical means.
A typical atom has a nucleus made of positively charged protons and neutral neutrons.
Negatively charged electrons orbit the nucleus.
The number of protons defines the element.
Atoms of the same element can have different numbers of neutrons (isotopes).
Atomic size is approximately 100 picometers.
Most atomic volume is empty space.
Electrons do not always orbit the nucleus in perfect circles.
Atomic mass is primarily determined by protons and neutrons.
Electrons contribute negligibly to atomic mass.
Atoms with equal numbers of protons and electrons are electrically neutral.
An imbalance in the number of protons and electrons creates an ion.

Diatomic Molecules: Made of two atoms (e.g., O₂).
Polyatomic Molecules: Made of more than two atoms (e.g., H₂O).
Macromolecule: Very large molecules consisting of subunits (e.g., proteins and DNA).

Covalent Molecules: Atoms connected by covalent bonds.
- In pure covalent, atoms have the same electronegativity.
- In polar covalent, atoms have slightly different electronegativities.
- Examples: H₂, O₃, H₂O, HCl
Ionic Molecules: Atoms connected by ionic bonds; metals and nonmetals (with exceptions).
- Cations and anions show large differences in electronegativity.

Molecules are electrically neutral, having equal numbers of protons and electrons.
Ions have unequal numbers of protons and electrons, resulting in a positive or negative charge.

Elements are substances composed of only one type of atom.
Elements cannot be broken down into simpler substances through chemical reactions.
Elements are fundamentally defined by the number of protons.
Elements are represented by unique symbols, typically on the periodic table (e.g., C for carbon, O for oxygen).
There are currently 118 known elements.

Compounds are formed when two or more different elements combine in a fixed ratio.
Compounds can be broken down into their constituent elements through chemical reactions.
Compounds have different properties than the elements that make them up.
Examples: CO (carbon monoxide), CO₂ (carbon dioxide), H₂O (water)
Types of Compounds: covalent, ionic, and others

A chemical reaction involves breaking bonds in reactants and forming bonds in products to create new substances.
Reactants are the initial substances, and products are the resulting substances.
Chemical reactions are common in everyday life—food digestion, respiration, burning fuel.
Chemical reactions are categorized into several types (e.g., combustion, decomposition, neutralization, redox, precipitation, synthesis).

Chemical equations use symbolic representations to describe chemical reactions.
Elements are represented by their symbols (e.g., H₂ for hydrogen).
Compounds are represented by their chemical formulas (e.g., H₂O for water).
Chemical equations show the reactants and products, with the direction of the reaction using symbols (→, ⇌, or other).
Coefficients in front of the formulas show the relative number of molecules or atoms involved.