The Bohr Model of an Atom

Study Notes

The atomic number is equal to the number of protons in an atom's nucleus.
The number of electrons in a neutral atom is equal to the atomic number.
In a neutral atom, positive and negative charges cancel each other out, resulting in a net charge of zero.
Atomic numbers are listed on the periodic table of elements.

Electrons orbit the nucleus at specific distances (shells).
Each shell correlates to a distinct energy level.
Electrons closer to the nucleus have lower energy levels than those further from the nucleus.
Shells have a fixed maximum number of electrons.
The maximum number of electrons per shell can be calculated using the formula: Ne = 2n², where 'n' is the shell number

Valence electrons are those electrons in the outermost shell.
Valence electrons have higher energy and are less tightly bound to the atom compared to inner electrons.
When a valence electron gains enough energy, it can leave the atom.

Ionization is the process where a valence electron escapes the atom.
Atoms absorb external energy (e.g., heat or light) to raise the energy levels of electrons.
Outer electrons, like valence electrons (being loosely bound) can more easily jump to higher energy levels when energy is absorbed.

Insulators: Materials that do not readily conduct electricity.
Conductors: Materials that readily conduct electricity.
Semiconductors: Materials with conductivity between conductors and insulators.

In solids, the interactions between atoms create energy level bands.
Electrons occupy a valence band.
When gaining sufficient energy, electrons can jump to the conduction band.
The gap in energy between the valence and conduction bands is called the band gap.
The band gap is the energy needed for electrons to jump to the conduction band.
In conductors, the valence and conduction bands overlap.
In insulators, the band gap is large and requires high voltages to make the electrons jump to the conduction band.
In semiconductor, the band gap is small, allowing for electrons' movement by moderate energy.

Silicon is a semiconductor; copper is a conductor.
They differ in the number of valence electrons and the attractive force felt by these electrons.
Copper has valence electrons in a less tightly bound orbit, thereby taking less energy to become free electrons, unlike silicon.