Chapter 4 Atomic Structure

Atom Atom – smallest part of an element that retains the properties of that element. Atomic Theory – proposed by John Dalton. Elements are ____________________________ Compounds are _______________________________ made up of a collection of atoms. made up of a collection of molecules.

Model of Dalton’s Atomic Theory Atoms of Element A Atoms of Element B Mixture of Atoms of Element A and B Compound made by Chemically combining Element A and B

Subatomic Particles electron- (e - ) proton – (p + ) neutron – (n o ) negatively charged particle, has almost no mass. (negligible) positively charged particle, relatively heavy. (1amu) particle with no charge, relatively heavy. (1amu) mass of ______________ = mass of ______________ 1 proton1 neutron

Structure of the Atom Nucleus in the center of the atom. composed of protons and neutrons. heavy and dense. All mass of atom positively charged. Negatively charged electrons move around the nucleus. only outer electrons (valence) involved in forming chemical bonds. most of atom is empty space.

Atomic Number Number of protons Whole number on Periodic Table. Atoms are _________________ which means _________. electrically neutral#p + = #e - Ions are ______________which means ___________________________________. charged particles # p + doesn’t = # e - (# of electrons change)

Mass Number The approximate mass of an atom of an element. Mass # = #p + + #n o Sum of the mass of heavy particles (p + + n o ) amu - atomic mass unit - 1 amu = mass of a single proton or neutron. - 1/12 the mass of a Carbon atom with 6p + & 6n o. # neutrons = mass # - atomic #

Isotopes Atoms that have the same # of protons but different #’s of neutrons. Therefore they have different atomic masses. Different isotopes of an element are chemically alike. (atoms of the same element) When you round the atomic mass on the Periodic Table, you get the mass # of the most commonly occurring isotope of the element. Isotopes are ___________ which means ____________.neutral# p + = #e - The number of neutrons changes.

Example He 4 2 Mass # Atomic # or may be written as He-4 Mass# Note: The number of protons never changes; it is the number of protons that determines what element an atom is.

Atomic Mass Found on the Periodic Table It is the weighted average of the masses of all the naturally occurring isotopes of that element. The average atomic mass of an element _____________ _____________________________________________ whereas the mass number _______________________ _________________________________ is the weighted average of the masses of all the isotopes of an element. is the total number of protons and neutrons in one atom of an element.

Calculation of average atomic mass. For Element “X” isotopes mass #abundance x – % =.20 x – % = X (10)(.20) = X (11)(.80) = amu

You Try Copper (Cu) For Copper isotopes mass #abundance Cu % Cu % 63 Cu (63)(.691) = Cu (65)(.309) = amu

Chapter 4 The End