The Nuclear Atom and Subatomic Particles
Quick Notes
- Atoms consist of:
- A dense, positively charged nucleus containing protons and neutrons.
- Electrons moving in space around the nucleus.
- Protons: charge +1, mass ≈ 1
- Neutrons: charge 0, mass ≈ 1
- Electrons: charge −1, mass ≈ 0 (negligable)
- Protons and neutrons = nucleons
- AZX symbol: A = mass number, Z = atomic number, X = element symbol
- Neutral atom: protons = electrons
- Ion: electrons ≠ protons
- Electron mass is negligible compared to protons and neutrons
Full Notes:
Atoms are the smallest, indivisible units of elements and are composed of three fundamental subatomic particles:
- Protons (p⁺): Positively charged particles found in the nucleus. Their number determines the element’s identity (e.g., all hydrogen atoms have 1 proton, all oxygen atoms have 8 protons).
- Neutrons (n⁰): Neutral particles also found in the nucleus. Neutrons add mass but do not affect chemical properties.
- Electrons (e⁻): Negatively charged particles that exist around the nucleus in energy levels (shells). Their arrangement determines an atom’s chemical behaviour.
Subatomic Particles Overview
| Particle | Charge | Relative Mass | Location |
|---|---|---|---|
| Proton (p+) | +1 | 1 | Nucleus |
| Neutron (n0) | 0 | 1 | Nucleus |
| Electron (e−) | −1 | ≈0 (negligable) | Outside nucleus (shells/orbitals) |
- The nucleus contains nearly all the atom’s mass
- Electrons occupy most of the volume and are arranged in energy levels or orbitals
- Protons and neutrons are called nucleons
The AZX Nuclear Symbol
To represent atomic structure, we use the nuclear symbol:
Where:
- A = mass number (total protons + neutrons)
- Z = atomic number (number of protons)
- X = element symbol (e.g., H, C, Fe)
From this, you can calculate:
- Protons = Z
- Neutrons = A − Z
- Electrons:
- Neutral atom: electrons = protons
- Ion: adjust based on charge
- Positive ion (e.g., Ca2+): electrons = protons − 2
- Negative ion (e.g., Cl−): electrons = protons + 1
Examples
Example Carbon-12
126C
Protons = 6
Neutrons = 12 − 6 = 6
Electrons = 6 (neutral atom)
Example O2− ion
168O2−
Protons = 8
Neutrons = 16 − 8 = 8
Electrons = 8 + 2 = 10
Example Fe3+ ion
5626Fe3+
Protons = 26
Neutrons = 56 − 26 = 30
Electrons = 26 − 3 = 23
Extra Notes
- The mass of the electron is so small compared to protons and neutrons that it's often considered zero in atomic mass calculations.
- Different atoms behave differently in chemical reactions due to the number and arrangement of electrons, especially in the outer energy levels.
Summary
- Atoms contain protons, neutrons, and electrons.
- Protons and neutrons are in the nucleus; electrons occupy shells.
- AZX notation shows atomic and mass numbers.
- In ions, electrons differ from protons depending on charge.
Linked Questions
What determines the different chemical properties of atoms?
The chemical properties of atoms are determined primarily by their electron configuration, especially the number and arrangement of electrons in the outermost shell (valence electrons). Atoms with similar valence electron structures exhibit similar reactivity and bonding patterns. Differences in nuclear charge and shielding also influence how strongly atoms attract or lose electrons, leading to variations in ionisation energy, electronegativity, and chemical behaviour across the periodic table.
How does the atomic number relate to the position of an element in the periodic table?
The atomic number represents the number of protons in an atom’s nucleus and determines its identity and position in the periodic table. Elements are arranged in order of increasing atomic number, which corresponds to the sequential filling of electron shells and sublevels. This organisation produces repeating (periodic) patterns in chemical and physical properties, as elements with similar outer electron configurations appear in the same group or column.