1. Structure of Atoms
Chapter 3.2

2. Objective 1:
Describe the evidence for the existence of electrons, protons, and neutrons, and describe the properties of these subatomic particles.
Define atom: smallest particle of an element that retains the chemical properties of that element.
Subatomic particles:
Protons
Neutrons
Electrons

3. Discovery of the Electron
Late 1800’s – J.J. Thomson discovered the electron through experiments with cathode-ray tubes.
Electron Properties
Relative Charge Mass Number actual mass
x kg
Plum Pudding
Model of atom

4. Discovery of Atomic Nucleus
In 1911 – Ernest Rutherford – Gold Foil Experiment
Showed that there was a small – dense positively charged nucleus of an atom.
Proton Properties
Relative Charge Mass Number actual mass
x kg

5. Neutrons Neutron Properties Discovered in 1932 by James Chadwick
British Scientist
Neutron Properties
Relative Charge Mass Number actual mass
x kg

6. The Atom
Nuclear Forces – Short range proton-neutron, proton-proton, and neutron-neutron forces that hold the nuclear particles together
Sizes of Atoms
Nucleus compared to rest of atom - approximately size of marble compared to a large football stadium.
Atom is mostly empty space

7. Objective 2
Discuss atoms of different elements in terms of their numbers of electrons, protons, and neutrons, and define the terms atomic number and mass number
Atomic Number (Symbol – Z)
Number of protons in nucleus of atom
Determines the identity of the atom!!!!!
C - 6
He - ___
F - ___
Pb - ___
Use periodic table to find these!
Since atoms are neutral, atomic number is also number of electrons
So C also has 6 electrons
He - ____ electrons

8. Objective 3
Define isotope, and determine the number of particles in the nucleus of an atom.
Isotopes
All Hydrogen atoms contain 1 proton
Many naturally occurring elements can contain different numbers of neutrons.
Isotope – at0ms of the same element that have different masses. n n n
Protium %
Deuterium
0.015 %
Tritium
Trace
Three isotopes of Hydrogen

9. Mass Number What is the mass number deuterium and tritium?
Mass number – total number of protons and neutrons in the nucleus of an isotope
Symbol – A
Protium has 1 proton and 0 neutrons
Mass number = #p + #n =
= 1
What is the mass number deuterium and tritium?
Find on periodic table

10. Determine the number of particles in an atom
How many protons, electrons, and neutrons are present in an atom of copper whose atomic number is 29 and whose mass number is 64?
How many protons and electrons are in an atom of sodium whose atomic number is 11?
An atom has 13 protons and 14 neutrons. What is its mass number?
Calculate the mass number for an atom that has 45 neutrons and 35 electrons.

11. Designating Isotopes Number of protons Neutrons Electrons 92 143 92
Hyphen Notation
Name of atom – mass number
Uranium - 235
Nuclear symbol
A X A : mass number, Z : atomic number, X : symbol of element
235U Z 92
Number of protons Neutrons Electrons
Nuclide – general term for any isotope of any element

12. Determine the number of particles in isotopes.
Calculate the numbers of protons, electrons, and neutrons in oxygen – 17 and in oxygen – 18.
Chlorine has two stable isotopes, chlorine – 35 and chlorine – 37. The atomic number of chlorine is Calculate the numbers of protons, neutrons, and electrons each isotope has.
Calculate the numbers of protons, electrons, and neutrons for each of the following isotopes of calcium : Ca and Ca 42 44 20 20