Inside the AtomInside the Atom

Particle Physics Lesson 1Particle Physics Lesson 1

Homework (Fri 2nd Oct)

Ernest Rutherford

What important experiment did he direct in the early 20th Century?

What did Rutherford conclude from his analysis of the observations?

VideoVideo

In Search of Giants (1 of 15) Atoms In Search of Giants (1 of 15) Atoms and the Periodic Tableand the Periodic Table

Quick ExerciseQuick Exercise

Draw a diagram of a lithium atom, Draw a diagram of a lithium atom, labelling as many parts as you can.labelling as many parts as you can.

Atoms in a Crystal...Atoms in a Crystal...

This is an image of This is an image of silicon atoms silicon atoms arranged on a face arranged on a face of a crystal. of a crystal.

The image was The image was made by a made by a Scanning Scanning Tunnelling Tunnelling MicroscopeMicroscope

Draw a lithium atom

This is the layout of a lithium atom, with three protons, three electrons, and four neutrons.  The protons and neutrons are, of course, found in the nucleus.  They are called nucleons.  The electrons are found in shells orbiting the nucleus.

Today’s ObjectivesToday’s Objectives

State the charge and mass in SI units and State the charge and mass in SI units and relative units for the proton, neutron and relative units for the proton, neutron and electron. electron.

Define specific charge and calculate its value Define specific charge and calculate its value for nuclei and ions. for nuclei and ions.

Interpret nuclide notation including the Interpret nuclide notation including the Proton number Proton number ZZ and the nucleon number and the nucleon number A. A.

Define what is meant by isotope.

Important FactsImportant Facts

It is important to understand: It is important to understand: The nucleus is very small compared to The nucleus is very small compared to

the atom, about 10 000 times smaller.  the atom, about 10 000 times smaller.  The diameter of an atom is in the order The diameter of an atom is in the order of 10of 10-10-10 m, whereas the diameter of the m, whereas the diameter of the nucleus in the order of 10nucleus in the order of 10-15-15  m.  m.

The atom is a very dynamic entity.  The The atom is a very dynamic entity.  The diagram shows a stylised diagram shows a stylised representation; the reality is that there representation; the reality is that there is absolute bedlam at the atomic level.is absolute bedlam at the atomic level.

Inside the atom…Inside the atom…

PropertyProperty ElectronElectron ProtonProton NeutronNeutron

ChargeCharge -1-1ee +1+1ee 00

MassMass 9.11 × 109.11 × 10--

31 31 kgkg1.67 × 101.67 × 10--

2727 kg kg1.67 × 101.67 × 10--

2727 kg kg

Relative Relative MassMass

0.00050.0005 1.00001.0000 1.00041.0004

The electron and the proton have the same value of charge, but the signs are different.  We also use a quantity for the charge called electronic charge unit, e.                     1 e = 1.602 × 10-19 C.

The neutron has almost the same mass as the proton.

Quick Quiz

1) How many protons neutrons and electrons are there in the lithium atom? 

2) A carbon atom has 6 protons and 6 neutrons.  Draw out the carbon atom in a similar way to the lithium atom in the diagram above.

3) What is the total charge of a carbon nucleus?(a) in electronic charge units(b) in coulombs4) What is the total charge of the electrons?(a) in electronic charge units(b) in coulombs

Definition of an IsotopeDefinition of an Isotope

Isotopes are atoms with the same number of protons and different numbers of neutrons.

Different atoms are distinguished by their numbers of protons and neutrons.  We write the symbols using the following notation:

A is called the nucleon number, or the mass number.  It is the total number of nucleons. Z is the proton number or the atomic number, which is the number of protons.  The number of protons determines the element. X is the chemical symbol

Isotope Notation

Isotope Notation We can determine the number of neutrons

simply by subtracting the proton number from the nucleon number.  ( No. of neutrons = A – Z).

Isotopes have the same numbers of protons, but different numbers of neutrons.

Isotopes have the same physical and chemical properties.

If the proton number is altered, the element changes.

Some isotopes are radioactive, as the nuclei are unstable. 

Specific Charge

The specific charge of a charged particle is defined as its charge divided by its mass:-

Calculate the specific charge for:-1) A hydrogen nucleus (1H).2) A uranium nucleus (238U)3) The electron.4) Doubly ionised 24Mg (mass is 3.98 x 10-26

kg).

mass

charge charge specific

Further QuestionFurther Question

An ion has a specific charge of 1.20 × 10An ion has a specific charge of 1.20 × 1077 C C kgkg-1 -1 and a charge of - 3.2 X 10 to the power of and a charge of - 3.2 X 10 to the power of minus 19 C. minus 19 C.

Express the charge in eExpress the charge in e Calculate the mass?Calculate the mass? This is likely to be an ion of which element?This is likely to be an ion of which element? What is the specific charge of the nucleus of What is the specific charge of the nucleus of

this ion?this ion? What would be the charge of an atom of this What would be the charge of an atom of this

element?element?

Reactions Chemical reactions involve the electrons

of the outer shells.  Nuclei are not involved in any way, and remain totally unaltered even in the fiercest chemical reactions.

Try this out…  Carbon 14 is an isotope of Carbon. How many protons? How many neutrons? How many electrons?

Write out Carbon-14 using the isotope notation.

Carbon 14 is an unstable isotope.  It decays so that one of the neutrons turns into a proton.

Draw the new atom, what is it? Write it out using the isotope notation.

Don’t mix up your ‘n’ words!

Nucleus – the massive positively charge centre of an atom

Neutron – an uncharged particle found in the nuclei of most atoms

Nucleon – a proton or a neutron in the nucleus

Nuclide – different types of nucleus of the same element but with different numbers of nucleons.

Summary