This site is about helping people understand the core ideas in chemistry so that they can succeed in a general chemistry course or enhance their general knowledge in science. I try to explain things in PLAIN ENGLISH and with VISUALS in a way that we can all understand. Below is a list of core chemistry concepts organized by topics. You can also choose a category from the side bar on the right
Why Students Think Chemistry is Difficult
Top Reasons Why Students Think Chemistry is Difficult?
Effective ways to Study and Understand Chemistry
Top Ideas on How to Learn Chemistry
Levels of Representation in Chemistry
What’re the Three Levels of Representation in Chemistry?
Structure and Composition of Matter
What’s an Atom?
What’s an Element?
What’s a Compound?
What’s a Molecule?
What’s a Mixture?
What’s a Pure substance?
If a substance is homogeneous, is it a pure substance?
How to Identify Matter
How can Matter be Identified?
How to Classify Matter
How can Matter be Classified?
Changes Matter Undergo
What Changes can Matter go through?
What major factor can affect the changes matter undergo?
When ice (water) is heated, does its temperature rise continuously?
When steam (water vapor) cools, does its temperature drop continuously?
What happens to water vapor as temperature decreases or as it cools?
Why does matter exists in different phases?
What molecular processes are involved when water cycles through the earth?
How to interpret and analyze a phase diagram
Units and Measurement
What’re SI units?
How to convert from one unit to another
Error: what is it and what are the types of errors in measurement?
Significant figures and uncertainty
Atomic Theory and Structure of an Atom
How did the Atomic theory develop?
What three fundamental laws of matter led to the development of the atomic theory?
What’s Rutherford atomic model?
What’s Dalton atomic theory?
What’s Thomson atomic model?
What’s Bohr atomic model?
What’re the properties of subatomic particles?
How was the charge and mass of an electron calculated?
How to calculate the number of protons, electrons, and neutrons in a neutral atom
Atomic Mass and Mole Concept
What’s atomic mass
Why do chemists need the Mole concept?
How to calculate moles and atoms of an element
How to calculate number of moles and molecule in a sample of molecule
How to calculate mass of an element present in atoms of that element
How to calculate mass of a compound present in molecules of the compound
How to calculate atomic mass
How to calculate percentage abundance from atomic and isotopic masses
How to calculate atomic mass of an isotope given the isotopic mass and percentage abundance of another
What is molar mass and how to calculate it for a hydrate
How to calculate percentage composition
How to interpret and use a chemical formula to write ratio identities
Empirical formula: what is it and how to find it from percentage composition and molecular formula
How to determine empirical formula from combustion analysis
Hydrate: what is it and how to calculate the percent of water in it
How to determine the empirical formula or water of crystallization of hydrate
Atomic Orbitals, Energy Levels, and Electron Configuration
How’re the orbitals in an atom arranged?
How’re atomic orbitals filled with electrons?
Valence, Valence Electrons, and Periodic Table
What’s the periodic table?
What’s the valence of an atom?
How to use periodic table to determine an element’s valence electrons
How Atomic and Ionic Size Vary
Can a cation or anion be larger than its neutral atom?
How does atomic size vary across and down the periodic table?
How do atoms form ions?
How to calculate the number of electrons in an ion
What is electron affinity and how does it trend on the periodic table?
What is ionization energy and how does it trend on the periodic table?
Why do atoms bond with one another?
What’s a chemical bond?
How do atoms form covalent bond?
Can atoms share electrons unequally in a covalent bond?
How hydrogen atoms form covalent bond
General rules on how to write Lewis structures
Using Lewis dot diagrams to explain bonding
Exceptions to the octet rule when writing Lewis structures
Formal charge: what is it and how to determine it
How do atoms form ionic bond?
What’re Vander Waals forces?
What’re dipole-dipole forces?
Why’re some bonds or molecules polar?
What is capillary action, and which three types of forces are responsible?
What is metallic bonding? Using the “electron sea” model to explain it
Properties of Molecular and Ionic Compounds
What are the properties of molecular and ionic compounds?
How valence electrons determine molecular shape
Types and General Properties of Chemical Reactions
Is a chemical reaction the same as a chemical change?
What’re the four types of chemical reactions?
What’s a chemical equation?
What’s reaction rate and what factors can affect it?
When do reactions reach chemical equilibrium and why does chemical equilibrium occur?
How to interpret a chemical formula in terms of mole and molecules
How to interpret a chemical equation in terms of moles to write mole-mole ratio
Using a chemical equation to convert from moles of one chemical to molecules
Using a chemical equation to convert from moles of one chemical to moles of another in stoichiometry
Using a chemical equation to covert from mass of one substance to mass of another in stoichiometry
How to determine limiting reactant
How to calculate theoretical and percentage yield
How to use particle models to determine the amount of excess reactant left over after the limiting reactant is completely used up in a reaction
How to solve solution stoichiometry step-by-step to determine the Molarity of a chemical when only its volume and molarity and volume of another are known in the balanced chemical equation
How to solve solution stoichiometry step-by-step to determine the volume of a chemical when only its Molarity and mass of another are known
What is stoichiometry, and how is it related to the mole concept?
How to Prepare and Calculate Solution Concentration
How to calculate solution in mass percent
How to calculate solution concentration in Molarity
How to prepare a chemical solution from scratch
Why does one chemical dissolve in another?
How does Sodium chloride (NaCl) dissolve in water?
How to prepare a solution from stock
What is Molality, how different is it from Molarity, and how do you calculate it?
What is solubility, and how does temperature and pressure affect the solubility of gases and solids?
How to calculate solution concentration in mole fraction
Why does salt solution conduct electricity, while sugar solution doesn’t?
What’s the difference between a strong and a weak electrolyte?
Acids and Bases
Properties of acids and bases
What’s the difference between strong and weak acids?
Why’re hydrochloric acid, nitric acid, and sulfuric acid strong acids, while hydrofluoric acid and acetic acid weak acids?
Why’s sodium hydroxide a strong base, while ammonia a weak base?
When is solution acidic or basic?
What’s the concentration of water molecules in water?
How can water make an aqueous solution acidic or basic?
How acidic or basic is an aqueous solution?
What’s the pH concept?
How do you calculate the pH of strong acid?
What’s Brønsted-Lowry’s concept of an acid and what’s Brønsted-Lowry’s concept of a base?
What is the concept of “conjugate” in acid-base chemistry?
Is conjugate acid always stronger than its conjugate base?
Buffer solution: what is it and how does it work to resist changes in its pH?
How do you calculate the pH of buffer solution?
How do you prepare a buffer solution of known pH from scratch?
General Properties of Gases
Factors to consider to study gas behavior
What’s atmospheric pressure?
General properties of gases
Why does the volume of gas increase as the temperature increase?
Can volume of gas become zero as its temperature decreases?
What’s the relationship between pressure and volume of gas?
What’s the relationship between pressure and temperature of gas?
What’s the relationship between pressure of gas and amount of gas?
What’s the relationship between volume and amount of gas?
What’s the ideal gas equation and what does it measure?
How to use gas laws to calculate amounts of gaseous reactants or products in a chemical reaction
How do you calculate the molar mass of a gas if you know mass, pressure, volume and temperature of the gas?
How to find mass using the ideal gas equation
How to find density using the ideal gas equation
Van der Waal’s equation and the significance of the constants a and b
What’s energy and why is it defined as the ability to do work?
What’s the law of conservation of energy? Using energy flow charts to make sense of this law
What’s the difference between temperature, cold, and heat?
How to apply the concept of “system and surroundings” to measure energy
Why do some reactions release energy, while others absorb energy from the surroundings?
Electromagnetic spectrum: what is it and what does it describe?
How are the ions in sodium chloride (NaCl) crystal arranged?
How to determine total atoms in unit cell to calculate volume and density of unit cell
What’re nuclear reactions and why do they occur?
Water hardness: what is it, what causes it, and how can it be removed?
How is energy transferred by heat
What are the mechanisms (ways) in which energy can be transferred by heat?
Vapor pressure: what is it, how does it develop, and what can affect it?
Why is it that the vapor pressure of salt water is lower than the vapor pressure of pure water?
How does the vapor pressure of solution depend on the concentration of the solute particles in it?
What is the colligative property vapor pressure lowering and to calculate it using Raoult’s law