⚡ Quick Revision: Elements at a Glance
- Elements cannot be broken into simpler substances by ordinary chemical methods.
- Iron, copper, oxygen, carbon and hydrogen are common elements.
- Elements are the building blocks of compounds.
Makeup: Iron contains only iron atoms; oxygen contains only oxygen atoms.
Hydrogen + Oxygen → Water
Observation: Two elements combine chemically to form a compound.
Element has one kind of atom vs Substance can be an element or a compound.
Do not write water as an element. Water is a compound made of hydrogen and oxygen.
ONE
One kind of atom = Natural building block = Element.
| Element | Type | Common Use / Recall |
|---|---|---|
| Iron | Metal | Used in tools and buildings |
| Copper | Metal | Used in electric wires 🔥 |
| Oxygen | Non-metal | Needed for breathing |
| Carbon | Non-metal | Found in coal and living things |
- Element is made of only one kind of atom.
- Elements are pure substances.
- Iron and copper are metals.
- Oxygen and carbon are non-metals.
- Elements combine chemically to form compounds.
⚡ Quick Revision: Chemical Symbols
- The first letter of a symbol is always capital.
- The second letter, if present, is always small.
- Chemical symbols make writing elements quick and universal.
Makeup: One capital letter represents the element Hydrogen.
Makeup: First letter capital N and second letter small a.
C + O₂ → CO₂
Observation: Symbols are used to write chemical reactions shortly.
C means Carbon vs Ca means Calcium.
Do not write NA for sodium. The correct symbol is Na, with only the first letter capital.
CAP-small
First letter CAPITAL, second letter small: Na, Fe, Cu, Ca.
| Element | Symbol | Memory Clue |
|---|---|---|
| Hydrogen | H | First letter |
| Oxygen | O | First letter |
| Carbon | C | Do not confuse with Ca 🔥 |
| Sodium | Na | From Natrium |
| Potassium | K | From Kalium |
- Chemical symbol is the short form of an element name.
- First letter is always capital.
- Second letter is always small.
- Na is sodium and K is potassium.
- C is carbon, but Ca is calcium.
⚡ Quick Revision: Compounds at a Glance
- Compounds are made by chemical combination of elements.
- A compound has properties different from its elements.
- Water, carbon dioxide and common salt are common compounds.
Makeup: 2 Hydrogen atoms + 1 Oxygen atom
Makeup: 1 Carbon atom + 2 Oxygen atoms
Makeup: 1 Sodium atom + 1 Chlorine atom
Hydrogen + Oxygen → Water
Observation: Two elements combine chemically to form the compound water.
Element has one kind of atom vs Compound has two or more elements chemically combined.
Do not call a compound a mixture. A compound has fixed composition and is formed by chemical combination.
CHEM-FIX
Compounds form by CHEMical combination in a FIXed ratio.
| Compound | Formula | Elements Present |
|---|---|---|
| Water | H₂O | Hydrogen + Oxygen 🔥 |
| Carbon Dioxide | CO₂ | Carbon + Oxygen |
| Common Salt | NaCl | Sodium + Chlorine |
- Compound contains two or more elements.
- Elements in compounds combine chemically.
- Compounds have fixed composition.
- Water is H₂O.
- Common salt is NaCl.
⚡ Quick Revision: Symbols, Formulae and Valency Recall
- Symbol represents one element; formula represents a compound.
- Valency helps us understand how elements combine.
- Numbers in formulae show the number of atoms present.
Makeup: 2 Hydrogen atoms + 1 Oxygen atom
Makeup: 1 Carbon atom + 2 Oxygen atoms
Makeup: 1 Carbon atom + 4 Hydrogen atoms
Makeup: 1 Sodium atom + 1 Chlorine atom
Carbon + Oxygen → Carbon Dioxide
Observation: The formula CO₂ shows carbon and oxygen are chemically combined.
Symbol represents an element vs Formula represents a compound.
Do not read H₂O as 2 oxygen atoms. H₂O means 2 hydrogen atoms and 1 oxygen atom.
S-E, F-C
Symbol for Element, Formula for Compound.
| Element | Symbol | Valency |
|---|---|---|
| Hydrogen | H | 1 |
| Oxygen | O | 2 🔥 |
| Nitrogen | N | 3 |
| Carbon | C | 4 |
| Sodium | Na | 1 |
| Item | Type | Meaning |
|---|---|---|
| H | Symbol | Hydrogen element |
| O | Symbol | Oxygen element |
| H₂O | Formula | Water compound 🔥 |
| NaCl | Formula | Common salt compound |
- Symbol represents an element.
- Formula represents a compound.
- Valency means combining capacity.
- H₂O means 2 hydrogen atoms and 1 oxygen atom.
- NaCl is the formula of common salt.
⚡ Quick Revision: Final Exam Recall Sheet
- 🔥 Element is made of only one kind of atom.
- 🔥 Compound is formed by chemical combination of two or more elements.
- 🔥 First letter of a chemical symbol is always capital.
Makeup: 2 Hydrogen atoms + 1 Oxygen atom
Makeup: 1 Carbon atom + 2 Oxygen atoms
Makeup: 1 Sodium atom + 1 Chlorine atom
Hydrogen + Oxygen → Water
Observation: Elements combine chemically to form a compound.
Carbon + Oxygen → Carbon Dioxide
Observation: Carbon and oxygen combine to form CO₂.
Symbol represents an element vs Formula represents a compound.
Do not write CO for cobalt in this level. Co is cobalt, while CO represents carbon monoxide.
E-S | C-F
Element has Symbol; Compound has Formula.
| Concept | Quick Recall | Exam Trap |
|---|---|---|
| Element | One kind of atom | Water is not an element |
| Compound | Elements chemically combined | Has fixed ratio 🔥 |
| Symbol | Short form of element | Na, not NA |
| Formula | Short form of compound | H₂O means 2H + 1O |
| Element / Compound | Symbol / Formula | Must Remember |
|---|---|---|
| Hydrogen | H | One-letter symbol |
| Sodium | Na | From Natrium 🔥 |
| Water | H₂O | 2 Hydrogen + 1 Oxygen |
| Common Salt | NaCl | Sodium + Chlorine |
Element → Symbol → Elements Combine → Compound → Formula
- Element has one kind of atom.
- Compound has two or more elements chemically combined.
- Symbol represents an element.
- Formula represents a compound.
- H₂O is water and NaCl is common salt.