Atom

Atoms

Atoms are the building blocks of matter. Everything around us is made up of atoms. The atom is more than a million times smaller than the thickness of a human hair. The smallest speck that can be seen under an ordinary microscope contains more than 10 billion atoms. Even though atoms are incredibly tiny, they are made up of even more minute particles: protons, neutrons, and electrons. These are called subatomic particles. Each element has a definite number of subatomic particles, which make up the center of the atom, called the nucleus.

The proton, a subatomic particle that carries a positive charge, is made up of 3 quarks. The proton is one of few particles that are stable alone. Protons positive charge is 1.602 x 10^-27 coulomb. Protons have a mass of 1.67 x 10^-27 kg. Along with neutrons, they account for most of the mass in atoms. The number of protons in the nucleus of an atom determines what kind of element it is. The atomic number of an element is equal to the number of protons in each atom's nucleus. Protons are affected by all four of the fundamental forces that govern interactions between particles and energy of the universe. The electromagnetic force arises from matter carrying an electrical charge. It causes positively charged protons to attract negatively charged electrons, and hold them in orbit around the nucleus of the atom. This force also causes closely packed protons in the nucleus of the atom to repel each other. This repulsion is over by the second fundamental force, strong nuclear force. Strong nuclear force binds the protons and neutrons together into a compact nucleus. The other two fundamental forces, gravitation and the weak nuclear force, also affect the proton. Gravitation attracts things with mass to each other. The weak nuclear force is a feeble force that governs how some particles break up into other particles.

The neutron, which is an electrically neutral particle, is roughly the same mass of a proton. The neutron and proton are tightly bonded together in the nucleus of the atom. Each atom usually contains about as many neutrons as protons, but different atoms of the same element may have different numbers of neutrons. All four fundamental forces of nature also affect electrons. Because it has mass, it is affected by gravity. Although the neutron has no electrical charge, it is slightly magnetic,