 Atoms of the same element with different numbers of neutrons.  What has changed if there is a different number of neutrons. HINT: look at your periodic tables. Something must have changed.

 If you have a different number of neutrons, that means your atomic mass has changed.  Remember that atomic mass = neutrons + protons  THE NUMBER OF PROTONS NEVER CHANGES.  Why doesn’t this number ever change?

 If you change the number of protons you now have a different element.  EX: If you have an atom of Ne (Neon) with 11 protons now.. You actually would have an atom of Na (Sodium)

 Protons  Neutrons  Electrons

 Protons  11  Neutrons  12  Electrons  11  Draw out the model

Sodium with 11 protons and 12 neutrons. ** This is what we see on the periodic table. Sodium with 11 protons and 13 neutrons. ** Different from periodic table

X : element symbol A: Mass Number # protons + # neutrons in the nucleus Always larger than Z A: Mass Number # protons + # neutrons in the nucleus Always larger than Z Z : Atomic number #protons Z : Atomic number #protons A, X, and Z are very important to remember!

 What is the element?  How many protons are in the element?  What is the elements atomic mass? Na 23 11

 What is the element?  Sodium  How many protons are in the element?  11  What is the elements atomic mass?  23 Na 23 11

 What is the element?  How many protons are in the element?  What is the elements atomic mass? Cl 33 17

 What is the element?  Chlorine  How many protons are in the element?  17  What is the elements atomic mass?  33 Cl 33 17

 An atom of Nitrogen  7 protons  Mass number of 14

 An atom of Nitrogen  7 protons  Atomic mass of 14 N 14 7

Sodium-23 Mass Number Element Name ** This is what we see on the periodic table

Questions, Comments, Concerns?

 Please take out your whiteboards.

 Write the isotope symbol for the chemical element that has 6 protons and 8 neutrons (write the symbol both ways)

Carbon – 14 C 14 6

 Write the isotope symbol for the chemical element that has 17 protons and 16 neutrons

Cl or Chlorine

 How many protons are in the isotope 54 Cr? (Chromium-54)

 24 just like all Chromium  Protons NEVER CHANGE

 Isotopes of an element always have the same number of neutrons.  A. False  B. True

 Isotopes of an element always have the same number of neutrons.  A. False

 Isotopes of an element always have the same number of protons.  A. False  B. True

 Isotopes of an element always have the same number of protons.  B. True

 Z = 9  A = 29  Draw the symbol.  How many protons?  How many neutrons?