Chapter 4

 Smallest part of an element that retains the properties of that element  all elements are made of indivisible atoms

 Two main regions of an atom: I. Nucleus II. Outer Cloud

I. Nucleus  Most of the atom’s mass  Very little space ~1/10,000 th the volume.  Contains two subatomic particles  Protons (+)  Neutrons (0)

 A. Protons (p + )  Found in the Nucleus  Positive Charge  Mass is 1 amu  Determines the element

B. Neutrons (n 0 )  Found in the Nucleus  Neutral Charge  Mass is the same as a proton  Determines nuclear stability

II. Outer Cloud  Most of the atom’s volume  Very little mass  Contains Electrons(-)

A. Electrons (e - )  Move around the nucleus in concentric shells  Negative Charge  Very Very Light!  Determines Basic Chemical Reactivity

 Atomic Number  The # of Protons  Found on the Periodic Table  The “Z” Number

 Atomic Number (must be whole #)  Give the atomic number for the following elements:  C  Be  Ca  Ar  He  Cu  Fe

 Mass Number  # of particles in the nucleus  The “A” number  # of Protons + # of Neutrons  This is not on the periodic table!  Example:  A carbon atom has 6 p + and 7 n 0. What is its mass number?

 Mass Number  Give the mass number for the following elements:  C: 6 p + and 6 n 0  Be: 4 p + and 3 n 0  Ca: 20 p + and 18 n 0  Ar: 18 p + and 21 n 0  He: 2 p + and 1 n 0  Cu: 29 p + and 34 n 0  Fe: 26 p + and 34 n 0

 Charge  Nucleus = + charge  Electrons = - charge  (opposites attract)  Usually the + and – charges exist in equal number  The atom is therefore “neutral”

 Charge  Ion = Charged Atom  + charge = cation  - charge = anion  A Negative ION = ANION

 Charge  Ion’s charge is determined by:  p + − e -  Example:  Nitrogen atom has 7 p + and 10 e -  Charge is:  -3

 Charge  Find the charge for the following elements:  Na: 11 p + and 10 e -  O: 8 p + and 10 e -  Al: 13 p + and 10 e -  Be: 4 p + and 2 e -  H: 1 p + and 0 e -  Cl: 17 p + and 18 e -  Ge: 32 p + and 28 e -

 Atoms with the same number of protons but different number of neutrons are isotopes.  Varied mass due to different numbers of n 0

 Isotopes  Can’t change # of protons  That would change the element  Can change # of neutrons  Compare  Carbon sample 1: 6 p + and 6 n 0  Carbon sample 2: 6 p + and 7 n 0  Carbon sample 3: 6 p + and 8 n 0  Which one is the isotope?  Answer: They all are!

 Atomic Mass  Weighted Average  Based on ALL isotopes of an element  This is why it is not a whole number  NOT the same thing as mass number

 Atomic Mass  Example: Chlorine has two naturally occurring isotopes:  75% Cl-35  25% Cl-37.  Atomic mass of Cl = amu

 Atomic Mass  Unit of Atomic Mass = AMU  1 AMU = 1/12 th the mass of Carbon-12

 How do we indicate what isotope we are talking about?  Top Left is for mass number  Bottom Left is for atomic number Cl Mass Number Atomic Number

 What if we had a chlorine atom with 17 protons and 18 neutrons?  Mass number = _______  Atomic number = ____________ Cl

 What if we had a magnesium atom with 12 protons and 13 neutrons?  Mass number = ____________  Atomic number = _____________ Mg

 Practice: Given the following elements, write the symbol with the mass number and atomic number in the proper locations.  C: 6 p + and 6 n 0  Be: 4 p + and 3 n 0  Ca: 20 p + and 18 n 0  Ar: 18 p + and 21 n 0  He: 2 p + and 1 n 0  Cu: 29 p + and 34 n 0  Fe: 26 p + and 34 n 0

 How else do we indicate isotope?  SymbolCl  Dash  Mass Number35 Cl-35

 An atom of Carbon has 6 protons and 8 neutrons. C-14

 How else do we indicate isotope?  NameChlorine  Dash  Mass Number35 Chlorine-35

 An atom of Hydrogen has 1 proton and 2 neutrons. Hydrogen-3

 On your worksheet, fill in the appropriate boxes as demonstrated by your instructor.

 Atomic number = # of protons  Mass number = protons + neutrons  Not the same thing as atomic mass!  Charge = protons - electrons

 If the # of electrons are changed  It becomes an ion  If the # of protons are changed  It becomes a different element  If the # of neutrons are changed  It is a different isotope