Applied Chapter 3.2 : Structure of Atoms

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