Formulas Flashcards
From Calculation in A'level text or just things to remember!!
How to know what is ionic
a metal (or ammonium) COMPOUND (has to be with something cannot be on its own) or an acid in solution * like HCl
Anything else NOT IONIC
always what?
BALANCE!! your chemical and IONIC equations, make sure it makes sense
simplify..
ionic equations if possible, they all must have divisible and equal numbers…so 2 2 2 in front of all three, or 3 3 3
magnesium in a CERTAIN case is not a metal compound i.e. it is by itself so
it is NOT IONIC, leave as is..Mg
sulphuric acid IS an acid in solution, so it
is ionic, write down the ions present
Magnesium Sulphate is a metal compound so
it is ionic, write down its ions as well
Hydrogen gas, is it ionic or not
it is not ionic, it does not fall into either possible class of ionic compounds, SO LEAVE IT ALONE
spectator ions
Cancel out spectator ions
Spectator ions are the same on both sides of the equation.
Here, Na⁺ (aq) and NO₃⁻ (aq) appear on both sides, so remove them.
Break down strong electrolytes (ionic compounds) into ions
Only aqueous (aq) compounds split into ions. Solids (s), liquids (l), and gases (g) stay the same
Calculating RAM when given percentage abundances that don’t add up to 100%
https://chatgpt.com/share/67d483e4-d144-8012-89f8-d27c254f9948
Brackets for formula
Rule of Thumb:
✔ No brackets for monatomic ions (e.g., SrCl₂, NaCl, MgBr₂)
✔ Use brackets for polyatomic ions when more than one is needed (e.g., Ca(OH)₂, Al₂(SO₄)₃)
Why no brackets in SrCl₂?
Strontium chloride (SrCl₂) consists of:
Strontium ion: Sr²⁺
Chloride ion: Cl⁻
Since chloride is a single atom ion (monatomic ion), we just write SrCl₂—no brackets needed.
Why brackets in Ca(OH)₂?
Calcium hydroxide (Ca(OH)₂) consists of:
Calcium ion: Ca²⁺
Hydroxide ion: OH⁻ (which is a polyatomic ion, meaning it contains more than one atom)
Since we need two hydroxide ions to balance calcium’s 2+ charge, we put OH in brackets to show that the entire hydroxide group is doubled:
Hack for writing ionic equations 4 SIMPLE STEPS BROOOOOOOOO
Writing ionic equations can be easy if you follow this simple hack:
Quick Steps (Hack Method)
- Write the balanced molecular equation
Example:
- Break down strong electrolytes into ions
Only aqueous (aq) compounds split into ions. Solids (s), liquids (l), and gases (g) stay the same.
Example:
- Cancel out spectator ions
Spectator ions are the same on both sides of the equation.
Here, Na⁺ (aq) and NO₃⁻ (aq) appear on both sides, so remove them.
- Write the net ionic equation
What’s left is:
Tip: Always look for solids (precipitates), liquids, or gases—they don’t split into ions!
Would you like another example to try?
TIP!!
How to differentiate between covalent or ionic compounds (easy tip!)
- Check the Types of Elements Present
Ionic Compounds = Metal + Non-metal
Example: NaCl (sodium chloride), MgO (magnesium oxide), KBr (potassium bromide)
Covalent Compounds = Non-metal + Non-metal
Example: CO₂ (carbon dioxide), H₂O (water), CH₄ (methane)
2. Look for Polyatomic Ions (Ionic Clue)
3. Check the Electronegativity Difference (if needed)
Large difference (≥1.7) → Ionic
Small difference (<1.7) → Covalent
RFM of (e.g. cuso4) crystals
- 5 H20
5 × ((2×1)) + 16
5 (18)
Finding RFM (Mr) given percentage compositions
https://chatgpt.com/share/67d48e4e-ef58-8012-8fdf-35afe3a5e753
How to Calculate the Neutron-to-Proton (n/p) Ratio
The neutron-to-proton ratio (n/p ratio) is calculated using the formula:
n/p = N/Z
Where:
N = Number of neutrons
Z = Atomic number (number of protons)
**What is the atomic number of an element, which represents the number of protons in the nucleus. It determines the element’s identity on the periodic table.
Example Calculation
For carbon-14
- Atomic number = 6 (protons)
- Mass number = 14
- Number of neutrons = Mass number – Atomic number
= 14 - 6 = 8
Neutron-to-proton ratio:
8/6 = 1.33
This means carbon-14 has 1.33 neutrons per proton.
