1 Isotopes & Ions

What’s in an atom of a given element? An atom has three subatomic particles: Proton = positive (+) charge Neutron = no charge Electron = negative (-) charge

Where are the different subatomic particles in an atom? The protons & neutrons are found in the center of the atom in the nucleus. The electrons orbit the nucleus.

Opposites Attract Positive charges, such as protons, are attracted to negative charges, such as electrons (opposites attract) Like charges repel (positive charges repel other positive charges, and negative charges repel other negative charges)

What is the ATOMIC NUMBER? The number of protons found in the nucleus of an atom.

What is the ATOMIC NUMBER? The atomic number is unique to that element. No two elements have the same atomic number.

What is the MASS NUMBER? The number of protons and neutrons in the nucleus of an atom. THIS IS NOT ON THE PERIODIC TABLE! MASS NUMBER IS NOT ATOMIC MASS/WEIGHT!

Mass Number Mass Number = Protons + Neutrons What about electrons? Electrons are so small relative to the other subatomic particles we do not include them in an atom’s mass number.

Atomic Mass Units A unit used to compare the masses of atoms, has the symbol amu Approximately equal to the mass of a single proton or neutron

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

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

12 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

13 Atomic Mass Listed on the periodic table Gives the mass of “average” atom of each element Average atom based on all the isotopes and their abundance % Atomic mass is not a whole number Na 22.99

14 Ions Atoms with unequal numbers of protons and electrons Unequal protons and electrons result in an overall net charge

In a single atom, charge results from having either more electrons or less electrons than protons Less electrons than protons = positive charge (cations) More electrons than protons = negative charge (anions)

Example: The magnesium ion has two less electrons than protons Mg (Mg 2+ )

+ Notice how we write magnesium with a charge of positive 2:(Mg 2+ ) Ions are written as the element symbol followed by the charge as a superscript Examples: Fluorine negative 1 = F - Aluminum positive 3 = Al 3+ Oxygen negative 2 = O 2- Symbols for Ions