Atoms and Mixtures Made Simple: Chemistry Notes for Students
Materials
Atom
It is the basic unit of an element that takes part in a chemical reaction.
Structure of the Atom
The atom consists of:
Inner part (nucleus)
-
Outer part (shells)
The Inner Part (Nucleus)
The nucleus consists of two subatomic particles:
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Protons
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Neut
-
rons
The Outer Part (Shells)
The outer part is made up of shells (energy levels). They are named with letters of the English alphabet, beginning from K-shell, L-shell, M-shell, etc.
The Subatomic Particles
There are three subatomic particles in an atom:
| Subatomic Particle | Location | Charge |
|---|---|---|
| Proton | Nucleus | Positive (+1) |
| Neutron | Nucleus | Neutral (0) |
| Electron | Shell | Negative (−1) |
Protons
-
Found in the nucleus
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Electrically positive
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Number of protons = number of electrons
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Cannot be lost or gained
Neutrons
-
Found in the nucleus
-
No charge
-
Cannot be lost or gained
Electrons
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Found in the shells
-
Negatively charged
-
Very negligible mass
-
Move around the nucleus
-
Can be lost or gained
-
Number of electrons = number of protons
Atomic Number
The total number of protons found in the nucleus of an atom.
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Written as a subscript at the lower right corner of the symbol.
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Example: ₁H, ₆C
Atomic Mass Number
The total number of protons and neutrons in the nucleus of an atom.
-
Written as a superscript at the top right corner of the symbol.
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Example: ⁷H, ¹⁶O, ¹⁵Na
Electronic Configuration
The arrangement of electrons on the shells of an atom according to energy levels.
Why an Atom is Electrically Neutral
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Protons = positively charged
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Electrons = negatively charged
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Charges are equal but opposite → they cancel out
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Therefore, the atom has no charge
Comparing Subatomic Particles
| Protons | Electrons | Neutrons |
|---|---|---|
| Located in nucleus | Located in shells | Located in nucleus |
| Positive (+1) | Negative (−1) | Neutral (0) |
| Massive | Negligible mass | Massive |
| Cannot be lost/gained | Can be lost/gained | Cannot be lost/gained |
| Stationary | Move around nucleus | Stationary |
Ion
A charged atom.
Types of Ions
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Cation → positively charged ion
-
Anion → negatively charged ion
Differences Between an Atom and an Ion
| Atom | Ion |
|---|---|
| No charge | Has charge |
| Not coloured | May be coloured |
| Same number of protons & electrons | Different number of protons & electrons |
| Stable | Not stable |
Electronic Configuration (Ionic Consideration)
| Element | K | L | M | N | O | Gain/Lose | Charge |
|---|---|---|---|---|---|---|---|
| Hydrogen | 1 | L1 | +1 | ||||
| Helium | 2 | – | 0 | ||||
| Lithium | 2 | 1 | L1 | +1 | |||
| Beryllium | 2 | 2 | L2 | +2 | |||
| Boron | 2 | 3 | L3 | +3 | |||
| Carbon | 2 | 4 | L4 | +4 | |||
| Nitrogen | 2 | 5 | G3 | −3 |
Table of Elements (with Electron Configuration)
| Element | K | L | M | N | O | Group (Gr.) | Ion (Q) |
|---|---|---|---|---|---|---|---|
| Oxygen | 2 | 6 | G6 | Q −2 | |||
| Fluorine | 2 | 7 | G7 | Q −1 | |||
| Neon | 2 | 8 | G0 | Q 0 | |||
| Sodium | 2 | 8 | 1 | G1 | Q +1 | ||
| Magnesium | 2 | 8 | 2 | G2 | Q +2 | ||
| Aluminium | 2 | 8 | 3 | G3 | Q +3 | ||
| Silicon | 2 | 8 | 4 | G4 | Q ±4 | ||
| Phosphorus | 2 | 8 | 5 | G5 | Q −3 | ||
| Sulphur | 2 | 8 | 6 | G6 | Q −2 | ||
| Chlorine | 2 | 8 | 7 | G7 | Q −1 | ||
| Argon | 2 | 8 | 8 | G0 | Q 0 | ||
| Potassium | 2 | 8 | 8 | 1 | G1 | Q +1 | |
| Calcium | 2 | 8 | 8 | 2 | G2 | Q +2 |
NB:
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Anion → Negative ions
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Cation → Positive ions
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