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Structure of the Atom Sections 17.1-17.4 Review • Elements are made up of only one type of atom. • All elements are listed on the Periodic Table. • Each element is represented by its atomic symbol. Atomic Symbols • Some symbols come from the elements name. – Example: C is for Carbon • Others come from the element’s Latin name. – Example: •Au is for Gold (aurum) •Pb is for Lead (plumbum) About Atoms • Atoms are so small they can’t be seen with visible light. • Photographs of atoms can be seen by a scanning tunneling microscope. • The atom is actually made up of smaller subatomic particles. – Proton – Electrons – Neutrons The Nucleus • Nucleus contains protons and neutrons. • The electrons can be found surrounding the nucleus in the electron cloud. • Electrons are very far away from the nucleus. • There is actually a lot of empty space between the nucleus and electrons. Subatomic Particles Particle Charge Mass Compared to an Electron Actual Mass Electron -1 1 9.11 x 10-31 Proton +1 1836 1.673 x 10-27 Neutron 0 1841 1.675 x 10-27 Isotopes • The number of protons tells us the atomic number of the atom. • The mass number is the total number of protons and neutrons in the nucleus. • Atoms can have different numbers of neutrons. • Atoms that have different numbers of neutrons are called isotopes. Isotopes •There are three known isotopes of Hydrogen. 1 1 H 2 1 H 3 1 H 1 proton 1 proton 1 proton 0 neutrons 1 neutron 2 neutrons What do these numbers mean? Mass Number 7 3 Li Atomic Number How many protons does lithium have? How many neutrons does lithium have? Element Symbol Atomic Mass • The atomic mass is NOT the same as the mass number. • The atomic mass shown on the periodic table is an average of all the isotopes of that element.