1 The Atom Atomic Number and Mass Number Isotopes

LecturePLUS Timberlake2 Atomic Theory Atoms are building blocks of elements Similar atoms in each element Different from atoms of other elements Two or more different atoms bond in simple ratios to form compounds

3 Subatomic Particles ParticleSymbol Charge Mass amu Electron e Proton p Neutron n0 1

LecturePLUS Timberlake4 Location of Subatomic Particles cm electrons protons neutrons cm nucleus

5 Atomic Number Counts the number of protons in an atom

6 Number of Electrons An atom is neutral The net charge is zero Number of protons = Number of electrons Atomic number = Number of electrons

7 Mass Number Counts the number of protons and neutrons in an atom

8 Atomic Symbols Show the mass number and atomic number Give the symbol of the element mass number 23 Na sodium-23 atomic number 11

9 More Atomic Symbols O P Zn p + 15 p + 30 p + 8 n16 n35 n 8 e - 15 e - 30 e -

10 Link to Chemistry ; Periodic Table Represents physical and chemical behavior of elements Arranges elements by increasing atomic number Repeats similar properties in columns known as chemical families or groups

11 Link to Chemistry ; Periodic Table Na

12 Link to Chemistry ; Atomic Number on the Periodic Table 11 Na Atomic Number Symbol

13 All atoms of an element have the same number of protons 11 Na 11 protons Sodium

LecturePLUS Timberlake14 Isotopes Atoms with the same number of protons, but different numbers of neutrons. Atoms of the same element (same atomic number) with different mass numbers Isotopes of chlorine 35 Cl 37 Cl17 chlorine - 35 chlorine - 37

15 Atomic mass unit (amu) A scale designed for atoms gives their small atomic masses in atomic mass units (amu) An atom of 12 C was assigned an exact mass of amu Relative masses of all other atoms was determined by comparing each to the mass of 12 C An atom twice as heavy has a mass of amu. An atom half as heavy is 6.00 amu.

16 Link to Chemistry ; Atomic Mass Listed on the periodic table Gives the mass of “average” atom of each element compared to 12 C Average atom based on all the isotopes and their abundance % Atomic mass is not a whole number Na 22.99