Atomic Structure and Sub-atomic Particles

Practice flashcards covering the characteristics of electrons and protons, Thomson's and Rutherford's atomic models, and the concept of atomic number.

Electron ($e^-$)

A negatively charged sub-atomic particle found outside the nucleus with a charge of $-1.6 \times 10^{-19}\,C$ and a mass of $9.1 \times 10^{-31}\,kg$.

Thomson's Atomic Model Postulates

1. An atom consists of a positively charged sphere with electrons embedded in it. 2. Negative and positive charges are equal in magnitude, making the atom electrically neutral.

Proton ($p^+$)

A positively charged sub-atomic particle discovered by E. Goldstein (1886) with a charge of $+1.6 \times 10^{-19}\,C$ and a mass of $1.673 \times 10^{-24}\,gm$, which is approximately $2000$ times the mass of an electron.

Neutron ($n^0$)

A neutral sub-atomic particle (charge of $0$) discovered by J. Chadwick (1932) with a mass of approximately $1\,\text{unit}$.

Canal Rays (Anode Rays)

Positively charged radiations used in the experiment by E. Goldstein to detect the presence of protons in the atom.

Rutherford's Alpha Particle Experiment Conclusion: Mostly Empty Space

Most alpha particles passed through the gold foil undeflected, indicating that atoms are predominantly empty space.

Rutherford's Alpha Particle Experiment Conclusion: Nucleus

A few alpha particles deflected, and about $1$ in $12,000$ bounced back, revealing a small, dense, positively charged center called the nucleus.

Nucleus Size

The nucleus is extremely small, occupying negligible space compared to the empty space of an atom, measured at about $1/105$ the size of the atom.

Mass Concentration in Rutherford's Model

The entire atomic mass is concentrated in the nucleus, which contains both protons and neutrons.

Drawback of Rutherford's Model

Electrons revolving in well-defined orbits would lose energy and eventually fall into the nucleus, making the atom highly unstable.

Neil Bohr (1912)

The scientist who proposed a modified model of the structure of the atom to overcome the drawbacks of Rutherford's model.

Atomic Number ($Z$)

The total number of protons lying in the nucleus of any atom; it serves as the identity of an atom.

Neutral Atom Relationship

In a neutral atom, the number of protons and electrons are equal, and the atomic number ($Z$) equals the number of protons.