The Structure of the Atom

Atomic Theory Democritus & John Dalton J.J. Thomson Atomos: All matter is made of tiny indivisible particles J.J. Thomson Discovered electrons Plum Pudding Theory Atoms were positive areas Negatively charged electrons were randomly scattered in the atom

Rutherford’s Atomic Model Ernest Rutherford Discovered Nucleus Nuclear Model Nucleus: small, heavy, positive center of atom Electron cloud: area outside nucleus where electrons are located Mostly empty space e- +

Subatomic Particles Electron – negatively charged particle, smallest, light, in electron cloud Proton - positively charged pieces, heavy, in nucleus Neutron - no charge, same mass as protons, in nucleus

Subatomic particles Relative mass Name Symbol Charge Electron e- -1 1/1840 Proton p+ +1 1 Neutron n0 1 ***Relative Mass means compared to. *** A proton is 1840 times the mass of an electron.

How Atoms Differ

Counting the Pieces Atomic Number = p+ Mass Number = p+ + n0 determines kind of atom (fingerprint) Mass Number = p+ + n0 Number of e- = # of p+ when it’s a neutral atom (no charge)

Na 11 Sodium 22.99 From periodic table Using the example  11 is the atomic number There are 11 p+ in Sodium Na is the element symbol Sodium is the element name 22.99 is the avg. atomic mass This is NOT the mass number!!! 11 Na Sodium 22.99

Symbols Contain the symbol of the element, the mass number and the atomic number. Element Symbol X Mass number Charge Atomic number

F 19 9 Symbols Find the Mass # 19 Atomic # p+ 9 e- n0 9 9 10 Always the same Same b/c no charge 9 9 9 10 = mass # - p+ = 19 – 9 =

Br 80 35 Symbols Find the Mass # Atomic # 80 p+ e- 35 n0 35 35 45 = mass # - p+ = 80 - 35 =

Symbols A neutral element has an atomic number of 34 and a mass number of 78. What is the number of p+? number of n0? number of e-? Complete symbol. 34 78 Se Same as atomic # 44 78 - 34= 34 34 Same as p+

Symbols A neutral element has 91 protons and 140 neutrons what is the Atomic #? Mass #? # of electrons? Complete symbol. 91 Same as p+ 231 p+ + n0 = 91 + 140 231 91 Pa Same as p+ 91

Name-# Isotopic Notation Contain the symbol of the element, the mass number and the atomic number. All are neutral (no charge) Example: Sodium-24 Mass # Element Name Name-#

Sodium -24 Isotopic Notation Find the Mass # Atomic # 24 p+ e- 11 n0 13 = mass # - p+ = 24 – 11 =

Nickel -56 Isotopic Notation Find the Mass # Atomic # 56 p+ e- 28 n0 = mass # - p+ = 56 – 28 =

Charges If Neutral: Electrons tell you charge of the atom: Atomic # = p+ = e- Electrons tell you charge of the atom: Lose/Gain e-: changes charge, creates ions # e- < # p+: cation, lose e-, positive  ions # e- > # p+: anion, gain e-, negative  ions

Cl 36 - 17 Symbols Find the Mass # Atomic # 36 p+ n0 17 e- 17 19 18 = 36 – 17 = 18 Charge is -1 Gained 1 e-

Ca 42 +2 20 Symbols Find the Mass # Atomic # 42 p+ n0 20 e- 20 22 18 = 42 – 20 = 18 p+ - 2 = 20 - 2= Charge is +2 Lost 2 e-

Symbols An element has 76 electrons and 117 neutrons, and a charge of +2, what is the Atomic #? Mass #? # of protons? Complete symbol. 78 +2 195 Pt Charge is +2, lost 2 e-, e- + 2 = 76 + 2 = 195 p+ + n0 = 117 + 78 78 78 same as atomic #

Build an Atom Only 2 e- on first ring 8 e- on each ring after that Pick 2 atoms out of cup Cut out p+, n0 and e- Glue p+ & n0 in nucleus e- on rings around nucleus Add a dot of each in the legend Determine p+, n0, e-, mass # and atomic # for your atoms