The Structure of the Atom

Subatomic particles Subatomic particles are particles that are smaller than an atom Rutherford had predicted three subatomic particles to exist – Protons – Electrons – Neutrons

Protons A proton is a positively charged subatomic particle – It has a charge of +1 Rutherford concluded that the amount of positive charge varies among elements – Sodium has 11 protons, Carbon has 6 protons, etc. Each nucleus must contain at least one proton

Electrons An electron is a negatively charged subatomic particle It is found in the space outside of the nucleus Each electron has a charge of -1

Neutrons A neutron is a neutral subatomic particle that is found in the nucleus of the atom A neutron has no charge

Subatomic Particles in Elements Each element on the periodic table has a unique number of protons, electrons, and neutrons. We can figure out these unique values by knowing an element’s atomic number and mass number

Atomic Number Atoms of different elements have different numbers of protons The atomic number of an element represents the the number of protons in that element!

Atomic Number cont. Lithium has 3 protons

Atomic Number cont. Because an atom must have a neutral charge, the number of protons in an element must be the same amount of electrons in an element. Nitrogen has 7 protons and 7 electrons

Mass Number We know how to figure out the number of protons and electrons in an element, but what about the number of neutrons? We use the Mass number to figure out how many neutrons an element has

Mass Number cont. The mass number of an atom is the sum of the protons and neutrons in the nucleus of an atom. To find the # of neutrons, we must subtract the number of protons from the mass number (Remember that the atomic number = # of protons) # of neutrons = Mass number – atomic number

Mass Number cont. Aluminum’s mass number is ~27 14 neutrons in Al = 14