Such an attachement may form by attraction of the positively one atom for the negatively of another atom, or by the attraction of charged atoms, which are

Protons, electrons, ions.

Explanation: An atom is made up of three basic particles which are protons, electrons and neutrons. Protons have positive charges, electrons have negative charges while neutrons have no charge i.e.,neutrons are neutral. Protons and neutrons occupy the nucleus while electrons revolve around the nucleus in their orbits. The number of protons is equal to the number of electrons in a neutral atom, but when an atom loses an electron it becomes positively charged while when it gains an electron, it becomes negatively charged. These charged atoms are called ions.

in scientific notation, the value of the  speed of light in a vacuum

  will be written as 2.995 * 10^8. when this value is represented in the form of

  a * 10^b, then, a = 2.995 and b = 8.

the value of the speed of light in a vacuum given above can also be rounded up to approximately 300000000. in this case, the scientific notation will be written as 3 *10^8.