applied chapter 3.2 : structure of atoms
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Chapter 3.2
Structure of Atoms
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:
ProtonsNeutronsElectrons
Objective 1:
Late 1800’s – J.J. Thomson discovered the electron through experiments with cathode-ray tubes.
Electron Properties Relative Charge Mass Number actual mass
- 1 0 9.109 x 10-31 kg
Discovery of the Electron
Plum Pudding
Model of atom
In 1911 – Ernest Rutherford – Gold Foil ExperimentShowed that there was a small – dense positively
charged nucleus of an atom.
Proton Properties Relative Charge Mass Number actual mass
+ 1 1 1.673 x 10-27 kg
Discovery of Atomic Nucleus
Discovered in 1932 by James ChadwickBritish Scientist
Neutron Properties Relative Charge Mass Number actual mass
0 1 1.675 x 10-
27 kg
Neutrons
The AtomNuclear Forces – Short range proton-neutron, proton-proton, and neutron-neutron forces that hold the nuclear particles together
Sizes of AtomsNucleus compared to rest of atom -
approximately size of marble compared to a large football stadium.
Atom is mostly empty space
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 atomDetermines the identity of the atom!!!!!
C - 6He - ___F - ___Pb - ___
Use periodic table to find these!Since atoms are neutral, atomic number is also
number of electronsSo C also has 6 electronsHe - ____ electrons
Objective 2
IsotopesAll Hydrogen atoms contain 1 protonMany naturally occurring elements can
contain different numbers of neutrons.Isotope – at0ms of the same element that
have different masses.
n
Protium 99.985 %
Deuterium 0.015 %
Tritium Trace
Three isotopes of Hydrogen
nn
Objective 3Define isotope, and determine the number of particles in the nucleus of an atom.
Mass NumberMass number – total number of protons
and neutrons in the nucleus of an isotopeSymbol – A
Protium has 1 proton and 0 neutrons Mass number = #p + #n = 1 + 0 = 1
What is the mass number deuterium and tritium?
Find on periodic table
1. How many protons, electrons, and neutrons are present in an atom of copper whose atomic number is 29 and whose mass number is 64?
2. How many protons and electrons are in an atom of sodium whose atomic number is 11?
3. An atom has 13 protons and 14 neutrons. What is its mass number?
4. Calculate the mass number for an atom that has 45 neutrons and 35 electrons.
Determine the number of particles in an atom
Designating IsotopesHyphen Notation
Name of atom – mass numberUranium - 235
Nuclear symbol A
X A : mass number, Z : atomic number, X : symbol of element
235U
Nuclide – general term for any isotope of any element
Number of protons Neutrons Electrons
92 143 92
92
Z
1. Calculate the numbers of protons, electrons, and neutrons in oxygen – 17 and in oxygen – 18.
2. Chlorine has two stable isotopes, chlorine – 35 and chlorine – 37. The atomic number of chlorine is 17. Calculate the numbers of protons, neutrons, and electrons each isotope has.
3. Calculate the numbers of protons, electrons, and neutrons for each of the following isotopes of calcium : Ca and Ca
Determine the number of particles in isotopes.
20
42 44
20
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