Atoms and isotopes

• The structure of the atom as accepted today includes protons, neutrons and electrons, not evenly distributed in an atom.
• Protons, neutrons and electrons are arranged inside the atom as follows: Protons and neutrons are in the nucleus, and electrons are in shells.
• The mass of an atom is determined by the sum of the protons and neutrons in the nucleus, known as the mass number.
• Alpha  , Beta  and gamma  are types of radiation.
• A radioactive substance contains unstable nuclei (unbalance of protons and neutrons) that become stable by emitting radiation.
• Background radiation comes from various sources such as bricks, food, radon gas in the atmosphere, cosmic rays, and rocks.
• The atomic number or proton number is the smaller of the two numbers shown in most periodic tables.
• Hydrogen atoms always contain 1 proton, carbon atoms always contain 6 protons, and magnesium atoms always contain 12 protons.
• Each element has a definite and fixed number of protons.
• Changes in the number of particles in the nucleus (protons or neutrons) are very rare.
• Changes in the number of particles in the nucleus only take place in nuclear processes such as radioactive decay, nuclear bombs, and nuclear reactors.
• If the number of protons changes, then the atom becomes a different element.
• The sum of the protons and neutrons in an atom’s nucleus is the mass number.
• The mass number is the larger of the two numbers shown in most periodic tables.
• The mass number of an atom is determined by the sum of the protons and neutrons in the nucleus.
• The number of neutrons in an atom is calculated by subtracting the number of protons from the mass number and dividing by the atomic number.
• Isotopes have the same atomic number, but different mass numbers.
• The different isotopes of an element have identical chemical properties.
• Isotopes are atoms of an element with the normal number of protons and electrons, but different numbers of neutrons.
• Isotopes are atoms of an element with the normal number of protons and electrons, but different
• Some isotopes are radioactive.