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Understanding Atomic Structure of an Element What makes up the Elements of an Atom • An element is a material that cannot be broken down into any simpler substance • Thanks to Dalton, we know that an element is made up of Atoms that are all identical in mass and no two elements have the same mass • Then Thompson and Borh discovered subatomic particles • Neutrons (n) • Protons (p) • Electrons (e) How an Element is made up • The atom is made up of three subatomic particles existing in two main areas • Nucleus – Protons: a positively charged particle located inside the nucleus – Neutrons: contain no electrical charge and is located in the nucleus • Electron Shells/Orbitals – Electrons: Negatively charged particles that fill outer orbitals around the nucleus Make up of the Atom • The Nucleus (protons, neutrons) – Is only about 1/10,000 of the size of the atom • This is equivalent to a pea contained in a football field – The Nucleus makes up the majority of the mass of an atom • Electron Shells/Orbitals – An electron has only 1/1837th the mass of an proton or neutron – Electrons move around on specific patterns outside of the nucleus (the majority of the empty space in an atom) How to represent an element • Element: Lithium – Atomic #3 – This means • It has 3 Neutrons (n) • It has 3 Protons (p) • It has 3 Electrons (e) • The # of Protons is what determines what element you’re talking about Mass Number • Sometimes we will describe an Element by its mass # Mass # = Protons + Neutrons As long as we know two parts of the equations we can solve for the rest (keeping in mind that the # of Protons is always representative of which element you are dealing with) Electron Shell Capacities • Each electron shell/orbital can only hold so many electrons (aka, Energy Levels) – First Shell holds 2 electrons – Second shell holds 8 electrons – Third shell holds 8 electrons – Fourth shell holds 18 electrons Practice • Lets do the element Sulfur – Atomic #16 Valence Electrons -Valence electrons are those that are contained in the outer most shell/energy level -They play a very important role in understanding how a element will react with other elements in a reaction -A Valence electron shell is only happy when it contains a full amount of electrons Calcium: Atomic #20 2 valence electrons (would need sixteen more to have a full shell)