Each element is unique due to its atomic structure. Atoms consist of protons and neutrons located in the nucleus, and electrons outside the nucleus. The number of protons determines the element, while the total of protons and neutrons is the mass number. Isotopes are atoms of the same element with different numbers of neutrons.

1. Particles in the Atom Each element is chemically unique. To understand why they are unique, you need to know the structure of the atom (the smallest particle of an element) and the characteristics of its components .

2. Particles in the Atom Electrons (-) charge no mass located outside the nucleus Protons (+) charge 1 amu located inside the nucleus Neutrons no charge 1 amu located inside the nucleus

16. Mass number versus Atomic Mass Notice mass # is just the atomic mass rounded off. Atomic mass is the mass (in a unit called amu’s) of a single atom . Mass number is the atomic mass rounded off, and equals the number of protons and neutrons together. Atomic mass 35 45 35 80 35 Br 18 22 18 40 18 Ar 20 20 20 40 20 Ca e – n 0 p + Mass # Atomic # Ca 40.08 20 Ar 39.948 18 Br 79.904 35 Atomic mass

18. Isotopes are like identical twins. They are almost exactly alike but not quite. For example, below are two forms of carbon. Carbon-12 Carbon-13 Carbon 13 is heavier by one neutron than Carbon-12 = proton = neutron

19. 6 Li 7 Li Nucleus Electrons Neutrons 3 Protons 3 Electrons 3 Nucleus Electrons Neutrons 4 Protons 3 Electrons 3 3 p + 3 n 0 2e – 1e – 3 p + 4 n 0 2e – 1e – + + + Nucleus Neutron Proton Lithium-6 Nucleus Neutron Proton Lithium-7 + + +

23. 11 p+ 12 n° 2e – 8e – 1e – Na 8 p+ 8 n° 2e – 6e – O 4 p+ 5 n° Be 5 p+ 6 n° B 13 p+ 14 n° Al

25. IONS Created when an atom gains or loses one or more electrons It acquires a net electrical charge. Charge of ion= the number of protons - the number of electrons

26. ATOMIC STRUCTURE Yttrium 1- 17 14 6 Element Z M p e n +/- Formula Oxygen 14 25 137 4

27. http://www.colorado.edu/physics/2000/applets/a2.html