Ionic bonding is the strong electrostatic force of attraction between oppositely charged ions. Ions are formed when atoms gain electrons or lose electrons.
When atoms gain electrons, they become negatively charged particles or ions; these ions are called anions.
When atoms lose electrons, they become positively charged particles or ions; these ions are called cations.
Fig.1 – diagram shows ionic bond formation between Lithium and Fluorine ions. The Lithium ion forms when the Lithium atom loses 1 electron. This electron is given to the Fluorine atom. As a result, the Fluorine atom becomes a Fluorine ion.
What is covalent bonding?
A covalent bond is formed when two non-metal atoms share a pair of electrons. The shared electrons would usually be in the outer shells of the atoms.
Fig.2 – diagram shows covalent bond formation between two hydrogen atoms where each hydrogen atom shares a pair of electrons. A hydrogen molecule, H2 , is formed.
Key differences between ionic and covalent bonding
Photosynthesis is a chemical process by which plants convert carbon dioxide and water into glucose and oxygen using light energy from the Sun. Photosynthesis occurs in the chloroplasts found in plant cells.
The photosynthesis equation
Here is the chemical equation for photosynthesis:
Limiting factors
A limiting factor is a factor that affects the rate of photosynthesis of a plant.
Scientists use symbols in chemical equations to show what reactant(s) and product(s) are involved in a chemical reaction, what direction the reaction proceeds in, what physical states the reactant(s) and product(s) are in and what reaction conditions are involved (e.g. temperature, presence of a catalyst, time etc). This helps scientists to understand chemical equations and how to apply the equation practically if they want to carry out the reaction to obtain a product (or group of products) for commercial and research purposes.
Step-by-step balancing method with chemical equation example 1
Step 1) Here is an example of the combustion of methane, CH4 , which is an unbalanced equation:
CH4(g) + …O2(g) → CO2(g)+ …H2O(l)
(g) means the physical state of the chemical is in a gaseous state while (l) means the physical state of the chemical is in a liquid state. So methane, oxygen and carbon dioxide are in a gaseous state while water is in a liquid state.
The small number 4, which is called subscript 4, from CH4 , means there are four Hydrogen atoms covalently bonded to a Carbon atom.
Subscript 2 from O2 means there are two Oxygen atoms covalently bonded to each other.
Subscript 2 from CO2 means there are two Oxygen atoms each covalently bonded to a Carbon atom.
Subscript 2 from H2O means there are two Hydrogen atoms each covalently bonded to an Oxygen atom.
Step 2)
Next step I would do to balance the chemical equation is I would list the type of atoms and their number on the left hand side (LHS) of the equation and on the right hand side (RHS) of the equation.
CH4(g) + …O2(g) → CO2(g)+ …H2O(l)
Step 3)
I can see on the LHS there are 4 hydrogen atoms while on the RHS there are 2 hydrogen atoms. We can’t change subscript 2 on H2O to subscript 4 due to the way 2 hydrogen atoms are each bonded to an oxygen atom, we can instead double the number of water molecules to get 4 hydrogen atoms on the RHS. When we double the number of water molecules on the RHS, we also increase the number oxygen atoms on the RHS as well to get 4 oxygen atoms.
Step 4)
The last step is to now double the number of oxygen atoms on the LHS to get a total of 4 oxygen atoms.
Step 5)
So now the the complete balanced equation is:
CH4(g) + 2O2(g) → CO2(g)+ 2H2O(l)
What this equation tells the scientist is that 1 mole of methane molecule will react with 2 moles of oxygen molecules to produce 1 mole of carbon dioxide and 2 moles of water molecules. If you don’t know what a mole is, click on the following link below:
Congratulations! If you have read this far and followed the steps without any difficulty, you have fully understood balancing the chemical equation for combustion of methane.
Think of 1 mole as a way to group a very large amount of atoms/ ions/ molecules/ compounds similar to how we group people e.g. 1 class = 30 students , 1 football team (on the pitch) = 11 players.
Mole and its relationship to atomic mass unit of an element
If you look at the Periodic Table for an element, for example Iron (symbol Fe), you will notice the number 55.845 which is its atomic mass number; atomic mass number is g/mol units and that means that if you want 1 mole of Iron, you will need 55.845 g of it.
Fig.1
Fig. 2
Fig. 3
Let’s take a look at another example which is Carbon-12. Carbon-12 (which has an atomic mass of 12 g/mol) helps to provide a concrete example of 1 mole because 12 grams of carbon-12 is equal to 1 mole of carbon atoms (think of coal as that is made mostly of carbon). Other substances will have different masses to make up 1 mole e.g. because a sodium atom has an atomic mass unit of 22.99 g/mol , you would need 22.99 g of sodium metal to make 1 mole of sodium atoms. Another example is calcium which has an atomic mass unit of 40.08 g/mol so you would need 40 g of calcium metal to make 1 mole of calcium atoms.
Fig. 4 – Picture showing 12g of carbon measured which is equivalent to 1 mole of carbon-12 atoms
Example of a past paper question involving moles
Let’s have a look at a past paper question example from PhysicsAndMathsTutor.com based on a GCSE AQA Chemistry past paper:
Below is an example Mark Scheme of how to solve it:
So in Step 1 of the mark scheme, we want to find out the number of molecules from 1 mole of carbon atoms, not from 70 carbon molecules so first step is to calculate 1÷70 = 0.0142857 moles.
Step 2:
if 1 mole = 6.02214076 × 1023 atoms
then
0.0142857 x 1 moles = 0.0142857 x 6.02214076 × 1023 atoms
