Chemistry - Atoms


- Info:

- First there were electrons, protons and neutrons freely flyng around the world.

- In some cases electron and proton would fly close to each other, and if their relative speed and angle would be right,

electrical force would force the electron to start circling/orbiting around the proton.

- This process is very similar to planets orbiting the sun or satelites oribiting planets with the difference that electron and

proton are attracted with electrical force and planets are attracted with gravitational force.

- This electron and proton will now contine to fly around the world in this newly created structure called atom.

- Such simple atom would eventualy hit other electrons, protons and neutrons resulting in more complex atoms.

- In the center of each atom is nucleus consistent of protons and optional neutrons.

- Electrons circle around nucleus.

- Number of electrons is always equal to the number of protons.

- Neutrons are not electricly charged and it is possible that nucleus has no neutrons.

- Atom is also called chemical element.

- Each atom is distinguished by its atomic number, which is the number of protons in its nucleus.


- Specifying Atom:

- Atoms are specified like this:



- The bottom number represents the atomic number and it is the number of protons in nucleus.

- The top number represents the mass number and it is number of protons and neutrons in nucleus.

- The fact that there are no plus or minus signs anywhere means that number of electrons is equal to number of protons.


- Periodic table of chemical elements:

- There are 117 types of atoms known in the world.

- They are all listed in the Periodic table of chemical elements.


- Electron Shell:

- An electron shell may be thought of as an orbit followed by electrons around nucleus.

- Eeach orbit can contain only a fixed number of electrons

- All electrons in the same orbit have the same kinetic energy.

- Each orbit has different radius around nucleus

- Orbit must fill completely before electrons can be added to an outer orbit.

- Electron shells are labelled (K, L, M, N, O, P, Q) or (1, 2, 3, 4, 5, 6, 7) going from innermost shell outwards.

- Electrons in outer shells have higher average energy and travel further from the nucleus than those in inner shells.

- This makes them more important in determining how the atom reacts chemically and behaves as a conductor, because

the pull of the atom's nucleus upon them is weaker and more easily broken.

- Valence shell is the outer shell, that is the last outward shell that contains atoms.

- Atoms like to have full valence shells which motivates them to share atoms through covalent bonds.

- Each shell can have 2n2 electrons where n is the number of the shell which results in following table:


Shell number

Max number of electrons


212 = 2


222 = 8


232 = 18


242 = 32


252 = 50