What Is an Atom?

What Is an Atom?

1. Atoms are the basic units of matter and the defining structure of elements.

2. When were created?

   • Atoms were created after the Big Bang 13.7 billion years ago. As the hot, dense new universe cooled, conditions became suitable for quarks and electrons to form. Quarks came together to form protons and neutrons, and these particles combined into nuclei.

3. Nucleus

   • Discovered
     • The nucleus was discovered in 1911 by Ernest Rutherford, a physicist from New Zealand.
   • is a membrane-bound organelle that contains the cell's chromosomes.
   • The nucleus is held together by the strong force
     • This force between the protons and neutrons overcomes the repulsive electrical force that would otherwise push the protons apart, according to the rules of electricity.

4. Protons

   • Protons are positively charged particles found within atomic nuclei.
   • Discovered
     • Rutherford discovered them in experiments with cathode-ray tubes that were conducted between 1911 and 1919
   • Protons are about 99.86% as massive as neutrons.
   • The number of protons in an atom is unique to each element.

5. Neutrons

   • Neutrons are uncharged particles found within all atomic nuclei
   • Mass
     • A neutron's mass is slightly larger than that of a proton.
   • Discovered
     • Neutrons were found during experiments when atoms were shot at a thin sheet of beryllium.

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