4.3.A.1  Translating Balanced Chemical Equations into Symbolic Particulate Representations:

1. Chemical Equations and Stoichiometry:

i. Molecular Formulas:
A molecular formula writes down the number of atoms for each element which are present in a molecule, for example, in a
Water H₂O 2 hydrogen atoms + 1 oxygen atom
Glucose: C₆H₁₂O₆; 6 carbon atoms + 12 hydrogen atoms + 6 oxygen atoms
A chemical equation is the use of symbols and formulas of the reactants and products in a chemical reaction. For example:  2H2​ + O2​→2H2​O
It shows that two molecules of hydrogen gas react with one molecule of oxygen gas to produce two molecules of water.
The substances that are undergoing the chemical reaction are on the left.
Products are the substances that are formed as a result of the reaction (right side).
The coefficient in front of each molecule, such as the 2 in 2H₂O represents how many molecules (or moles) are present.

ii. Stoichiometry:
Stoichiometry is the determination of the amounts of reactants and products in a chemical reaction. It requires mole ratios, which are based on the balanced chemical equation.

iii. Mole Ratios: You can find the mole ratio from the balanced equation, which tells you how much of one substance reacts with, or is produced from, a given amount of another substance.

Reaction:  2H2 + O2 → 2H2O
The mole ratio of hydrogen to water is 2:2, or 1:1. So, for example, 1 mole of hydrogen reacts with 1 mole of water.
iv. Stoichiometric Steps:
a. Balance the chemical equation.
b. Convert quantities to moles. (Use molar masses if you’re given grams.)
c. Use the mole ratio from the balanced equation to find the number of moles of the desired substance.
d. Convert moles to the desired quantity (e.g., grams, molecules, liters).

2. Law of Conservation of Mass:

The Law of Conservation of Mass states that no new mass is made, and no old mass disappears during a chemical reaction. That is, the sum of masses of reactants equals the sum of masses of products. This rule of conservation of mass is important when one tries to balance a chemical equation; thus, it checks whether the same number of atoms for every element occurs on both sides of a chemical reaction.

Balancing a chemical equation is a process of adjusting the coefficients of the reactants and products to equalize the number of atoms of each element on both sides. This satisfies the Law of Conservation of Mass as no atoms are created or destroyed in the process.

i. How to Balance Chemical Equations:

a. Write the unbalanced equation. First, write the correct formulas of the reactants and the products.
b. To tally the total number of each type of element present on the reactant as well as on the product sides of the reaction equation.
c. Balance the atoms by changing the coefficients. Use coefficients (positive integers placed in front of compounds) to make the number of atoms of each element the same on both sides. Start with elements which appear in only one reactant and one product.
d. Check your work. After balancing, review the equation again. Make sure the number of atoms for each element is the same on both sides.

Example: Balance the Combustion of Methane (CH₄)

The unbalanced equation for the combustion of methane is:

CH₄ + O₂ → CO₂ + H₂O

Step 1: Count the atoms on both sides
Reactants:
C: 1 (from CH₄)
H: 4 (from CH₄)
O: 2 (from O₂)

Products:
C: 1 (from CO₂)
H: 2 (from H₂O)
 O: 3 (2 from CO₂ and 1 from H₂O)

Step 2: Balance the elements
Carbon is already balanced. There’s 1 carbon on each side.
Balance Hydrogen: There are 4 hydrogens in CH₄ but only 2 hydrogens in H₂O. To balance hydrogen, we need 2 H₂O molecules (because 2 × 2 = 4):

$$\boxed{{\displaystyle {\text{CH}}_4{\text{ + 2O}}_2\to {\text{CO}}_2{\text{ + 2H}}_2\text{O}}}$$

Balance Oxygen: Next, balance the oxygen atoms. In the products, we have 2 oxygen atoms from CO₂ and 2 oxygen atoms from 2 H₂O for a total of 4 oxygen atoms. We need to have 2 O₂ molecules on the reactant side (because 2 × 2 = 4):$${\text{CH}}_4{\text{ + 2O}}_2\to {\text{CO}}_2{\text{ + 2H}}_2\text{O}$$

Step 3: Double-check the atom counts:
Reactants:
 C: 1 (from CH₄)
H: 4 (from CH₄)
O: 4 (from 2 O₂)

Products:
C: 1 (from CO₂)
H: 4 (from 2 H₂O)
O: 4 (2 from CO₂ and 2 from 2 H₂O)

The equation is now balanced!

This is a balanced equation, and it follows the Law of Conservation of Mass. The number of atoms of each element is the same on both sides of the equation, and therefore no mass is lost or gained in the reaction.

Key Tips for Balancing:
Balance elements one at a time. Start with the most complex molecule and work your way to the simpler ones.
Use whole-number coefficients. Coefficients have to be whole numbers, so do not use fractions.
Check your work. Check that all atoms are balanced.

3. Particulate Representations:

Particulate representations are models that help us understand what is happening at the atomic, molecular, and ionic level in chemical reactions. These show what is occurring at the microscopic level, which is difficult to visualize when one only sees chemical formulas.

i. Types of Particule Representations:

a. Atoms and Molecules as Particles:
Usually, atoms and molecules are represented as isolated balls or groups of balls. In general, colors or sizes are used to symbolize different elements of atoms.
Atoms: Often small spheres are drawn with every color denoting a different element, such as oxygen as red, hydrogen as white, carbon as black.
Molecules: the atoms grouped together, and this is done, often in an idealised model, using lines to show atoms bonded together

Idea: A molecule of water can be represented in a diagram, for instance as two small white spheres joined to a larger red sphere. (These are drawn to scale).
b. Ions:
Ions are atoms or groups of molecules which have either gained an electron, hence ending up with a negative charge or lost an electron, and hence end up having a positive charge. These can be represented as charged particles.

Cations– positively charged ions: Represented by small spheres with the positive charge sign (+).
Anions – negatively charged ions: Represented as large spheres with the negative charge sign (−).

Example:
The sodium ion (Na⁺) can be represented as a smaller blue sphere with a positive charge.
The chloride ion (Cl⁻) can be represented as a larger green sphere with a negative charge.

b. Representation of a Chemical Reaction:

Atoms, molecules, or ions can be considered to rearrange to produce new substances in a reaction. These models help visualize how bonds break and form in a reaction.

Example 1: Water (H₂O) Formation:

The most common reaction of hydrogen gas (H₂) with oxygen gas (O₂) to form water (H₂O) is as follows:    2H2​ + O2​→2H2​O

Particulate Representation:
Reactants:
Two H₂ molecules: Each H₂ molecule contains two hydrogen atoms (2 small white spheres connected by a line).
One O₂ molecule: The O₂ molecule contains two oxygen atoms (2 red spheres connected by a line).

Products:
Two H₂O molecules. Each water molecule contains two hydrogen atoms (white spheres) and one oxygen atom (red sphere), all bent.

This would then demonstrate how the molecules of H₂ and O₂ are breaking apart and afterwards the atoms assemble themselves into H₂O molecules.

Example 2: Sodium Chloride Formation
NaCl can be made from the chemical reaction of Na with Cl, thus creating a bond:  Na + Cl → NaCl

 Particulate Representation:
Reactants:
Sodium (Na) as a blue sphere (Na atom), which has one lone electron to lose and result in a cation, Na⁺.
Chlorine (Cl) as a green sphere (Cl atom) with one lone electron that will be gained and form an anion, Cl⁻.

Products:
The sodium ion: a blue sphere with a plus charge.
The chloride ion is depicted as a green sphere with a minus (-) sign.
Na loses its electron, and Cl gains the same to form Na⁺ and Cl⁻. Since they are oppositely charged, they attract each other to form ionic compound NaCl.

Example 3: Salt Dissolved in Water (NaCl in H₂O)

In an aqueous solution, the ionic bonds of NaCl break, and it dissolves. Thus, the Na⁺ and Cl⁻ get surrounded by the molecules of H₂O.

Particle Diagram:

Reactants:
The NaCl is held together with ionic bonds and exists as a lattice of Na⁺ and Cl⁻ ions.
H₂O is drawn by the representation of two white spheres in a circle which denotes the hydrogen atoms and a red sphere denotes the oxygen atom.
Products:
The Na⁺ ions are surrounded by the negative end of water molecules and the positive ends of the hydrogen of the water molecules surrounded the Cl⁻ ions.
The water molecules “protect” the ions from each other, which means the Na⁺ and Cl⁻ do not recombine.

Benefits of Particulate Representations:
a. Explains Molecular Interactions: Allows people to see exactly how single atoms, molecules, or ions interact in a reaction.
b. Illuminates Bonding and Structure: Indicates how the atoms are disposed of as well as which bonds are broken and which are formed in the course of the reaction.
c. Helps Understanding Reaction Mechanisms: One gets an idea of the atomic perspective through which a reaction takes place; hence, complicated processes like dissociation, redox reactions, or catalysis become somewhat more approachable.

4. Ionic vs. Molecular Models: