Details on permanent fundamental particles, temporary fundamental particles, composite particles, isotopes, isobars, and isotones.
Examples: Hydrogen atom (H), Oxygen atom (O).
Examples: Positron, Neutrino, Antineutrino, Meson, etc.
Examples: Alpha particle (α-particle / 42He2+) and Deuteron particle (21H+).
Discovery: Discovered in 1897 by Sir J. J. Thomson through cathode ray tube (discharge tube) experiments.
Definition: The negatively charged fundamental particle revolving around the nucleus in specific energy levels (orbits) is called an electron.
Key Characteristics:
- Actual Mass: 9.1095 × 10−28 g or 9.1095 × 10−31 kg. This is approximately 1/1837 (or 1/1840) times the mass of a hydrogen atom or proton.
- Actual Charge: −1.602 × 10−19 C (Coulomb), −1.602 × 10−20 emu, or −4.8 × 10−10 esu.
- Relative Charge: −1
- Symbol: e− or 0−1e
Discovery: In 1886, Eugen Goldstein detected its existence while observing canal rays, and in 1919, Ernest Rutherford established it as a permanent fundamental particle of the atom.
Definition: The positively charged fundamental particle situated inside the atomic nucleus is called a proton.
Key Characteristics:
- Actual Mass: 1.6726 × 10−24 g or 1.6726 × 10−27 kg.
- Actual Charge: +1.602 × 10−19 C (Coulomb) or +4.8 × 10−10 esu.
- Relative Charge: +1
- Symbol: p, p+, 11H or 11p
Discovery: Discovered in 1932 by British physicist James Chadwick.
Definition: The electrically neutral (charge-free) fundamental particle situated inside the atomic nucleus is called a neutron.
Key Characteristics:
- Actual Mass: 1.6749 × 10−24 g or 1.6749 × 10−27 kg (the heaviest among the three permanent particles; approximately 1839 times the mass of an electron).
- Actual Charge: 0 (electrically neutral).
- Relative Charge: 0
- Symbol: n or 10n
- Special Note: Ordinary hydrogen or protium (11H) contains no neutron in its nucleus.
| Particle | Discoverer & Year | Location | Actual Charge | Relative Charge | Actual Mass | Relative Mass |
|---|---|---|---|---|---|---|
| Electron (e−) | J. J. Thomson (1897) | Energy levels outside nucleus | −1.602 × 10−19 C (−4.8 × 10−10 esu) |
−1 | 9.1095 × 10−28 g (9.1095 × 10−31 kg) |
1/1837 (0.000548 amu) |
| Proton (p) | Ernest Rutherford (1919) | Inside the nucleus | +1.602 × 10−19 C (+4.8 × 10−10 esu) |
+1 | 1.6726 × 10−24 g (1.6726 × 10−27 kg) |
1 (1.00727 amu) |
| Neutron (n) | James Chadwick (1932) | Inside the nucleus | 0 (Neutral) | 0 | 1.6749 × 10−24 g (1.6749 × 10−27 kg) |
1 (1.00866 amu) |
Definition: The subatomic particles that do not remain permanently inside an atom, but are created under specific conditions for an extremely short period and then decay or disappear, are called temporary fundamental particles.
Key Characteristics:
- Their lifespan or stability is extremely short.
- Their number in an atom is not fixed; scientists estimate their count to be around 100 or more.
- They do not participate in building the permanent structure of an atom.
Examples: Meson, Positron, Pion, Neutrino, and Antineutrino.
Definition: In addition to permanent and temporary fundamental particles, comparatively heavier and composite (compound) particles whose presence is occasionally observed in atomic nuclei are called composite particles.
Key Characteristics:
- They are not single elementary particles; rather, they are heavier particles formed by the combination of multiple particles.
- Their role is observed in nuclear reactions or during specific radioactive decays.
Examples:
- Alpha particle (α-particle): Di-positive helium nucleus (42He2+).
- Deuteron particle: Nucleus of heavy hydrogen (composed of one proton and one neutron: 21H+ or 21D+).
- Isotope (ends in ‘P’): Proton number is the same.
- Isobar (contains ‘B’ / Greek Baros = Weight): Mass number is the same.
- Isotone (ends in ‘N’): Neutron number is the same.
Definition: Atoms having the same number of protons (or atomic number) but different mass numbers due to differences in neutron numbers are called isotopes of each other.
Origin: Derived from Greek words Iso (same) and Topos (place); because they occupy the exact same position in the periodic table.
Key Characteristics:
- They are different atoms of the same chemical element.
- Since their electron configurations are identical, their chemical properties remain identical.
- Due to slight differences in mass, slight variations exist in their physical properties (e.g., boiling point, density).
- They occupy the same slot in the periodic table.
Examples:
- Hydrogen: Has a total of 7 isotopes, but 3 are found naturally:
- Protium or ordinary hydrogen (11H) — Number of neutrons = 1 − 1 = 0
- Deuterium (21H or D) — Number of neutrons = 2 − 1 = 1
- Tritium (31H or T) — Number of neutrons = 3 − 1 = 2
- Carbon: Has 3 naturally occurring isotopes: 126C, 136C, and 146C. The first two are stable, while 146C is radioactive.
- Oxygen: Has 3 stable isotopes: 168O, 178O, and 188O.
Definition: Atoms having the same mass number but different proton numbers and neutron numbers are called isobars of each other.
Origin: Derived from Greek words Iso (same) and Baros (weight or mass).
Key Characteristics:
- They are atoms of completely different chemical elements.
- Because their atomic numbers differ, their electron configurations and chemical properties are completely different.
- They occupy different positions in the periodic table.
Examples:
- 4018Ar, 4019K, and 4020Ca (Mass number is 40 for all)
- 146C and 147N (Mass number is 14 for both)
- 6529Cu and 6530Zn (Mass number is 65 for both)
Definition: Atoms having the same number of neutrons but different proton numbers and mass numbers are called isotones of each other.
Key Characteristics:
- They are atoms of different chemical elements.
- Because their proton and electron counts differ, their chemical properties are different.
- They occupy different positions in the periodic table.
Examples:
- 3014Si, 3115P, and 3216S
- Number of neutrons in 3014Si = 30 − 14 = 16
- Number of neutrons in 3115P = 31 − 15 = 16
- Number of neutrons in 3216S = 32 − 16 = 16
- 146C and 168O (Neutron count for both = 14 − 6 = 16 − 8 = 8)
- 31H and 42He (Neutron count for both = 3 − 1 = 4 − 2 = 2)
| Property / Aspect | Isotope | Isobar | Isotone |
|---|---|---|---|
| Proton Number (Z) | Same | Different | Different |
| Mass Number (A) | Different | Same | Different |
| Neutron Number (N = A − Z) | Different | Different | Same |
| Identity of Elements | Atoms of the same element | Atoms of different elements | Atoms of different elements |
| Position in Periodic Table | Same position | Different positions | Different positions |
| Chemical Properties | Identical / Same | Different | Different |
| Key Examples | 11H, 21H, 31H 126C, 136C, 146C |
4018Ar, 4020Ca 146C, 147N |
3014Si, 3115P, 3216S 146C, 168O |
