4.1 the atom and isotopes
TRANSCRIPT
Syllabus points “The nuclear model of the atom describes the atom as
consisting of an extremely small nucleus, which contains most of the atom’s mass, and is made up of positively charged protons and uncharged neutrons surrounded by negatively charged electrons”
“Nuclear stability is the result of the strong nuclear force, which operates between nucleons over a very short distance and opposes the electrostatic repulsion between protons in the nucleus”
Learning goals Define:
Nucleus, proton, neutron, electron, atomic number, mass number, atomic mass unit
State the mass of protons, neutrons and electrons in terms of the atomic mass unit
Calculate the number of neutrons, electrons and protons in an atom by using the atomic number and mass number
Convert between atomic mass units and kilograms Give the SI unit for: masses on the atomic or molecular scale Define:
Isotope, radioisotope, nuclide, nucleon, strong nuclear force, electromagnetic force
Recall that a large number of isotopes exist for each element Identify that isotopes have different physical properties Identify that the mass number on the periodic table represents the most stable
isotope/s of an element Explain how the strong nuclear force opposes the electrostatic repulsion between
the protons in a nucleus Identify that most isotopes of elements are radioisotopes Identify that stable isotopes are the most abundant isotopes
500 BC
Democritus
Leucippus
Atoms are indivisible
1808
John Dalton
Different arrangements =
different compounds
1904
J. J. Thomson
Plum pudding model
Early Ideas about matter
1911
Ernest Rutherford
Nuclear model
1913
Neils Bohr
Bohr model (orbiting electrons)
1920’sErwin
Schrödinger
Quantum model (electron orbits)
Current model Physicists have discovered that protons and neutrons are composed of even
smaller particles called quarks.
As far as we know, quarks are not made up of anything else. Fundamental particle, perhaps?
The Standard Model
Explains what the world is and what holds it together
All the known matter particles are composites of quarks and leptons, and they interact by exchanging force carrier particles
From www.livescience.com
Covered in detail in the Year 12 Physics course
Orbiting model of the atomFrom BoardWorks
The electrons orbit the nucleus in layers called shells.
The nucleus is where most of the mass of the atom is found. It contains protonsand neutrons.
Particles in an atom
Particle Mass Charge Location
Proton 1 amu(1.66 × 10-27 kg)
+ 1 Nucleus
Neutron 1 amu(1.66 × 10-27 kg)
0 Nucleus
Electron 5.5 × 10-4 amu(9.11 × 10-31 kg)
- 1 Electron cloud
Nucleon = components of a nucleus, protons and neutronsE.g. Each atomic nucleus consists of one or more nucleons
Nuclide = specific type of atoms or nucleiE.g. A set of nuclides with equal atomic number but a different number of neutrons, are called isotopes
Atomic Mass Unit Also represented by amu (atomic mass unit), u (unified atomic mass unit) or Da
(Dalton)
Standard unit that is used for indicating mass on an atomic or molecular scale
1 amu = the mass of a single proton or neutron
1 amu = defined as one twelfth of the mass of an atom of carbon-12
1 amu = 1.66 × 10−27 kg
Recap
Element Atomic Number
Mass Number
Number of protons
Number ofneutrons
Carbon
78
Use a periodic table to fill in the following table:
Recap
Element Atomic Number
Mass Number
Number of protons
Number ofneutrons
Carbon 6 12 6 6
Platinum 78 195 78 117
Use a periodic table to fill in the following table:
XA
Z
Mass number
Atomic number
Element symbol
Another way of representing atoms
Example 2 Rewrite the following elements in the format 𝑍
𝐴𝑋
Helium
Uranium-238
Carbon-12
Hydrogen
Example 2 Rewrite the following elements in the format 𝑍
𝐴𝑋
Helium 24𝐻𝑒
Uranium-238 92238𝑈
Carbon-12 612𝐻𝑒
Hydrogen 11𝐻
Isotopes The type of atom is determined by the number of protons in its
nucleus (e.g. all Carbon atoms have 6 protons in the nucleus).
Some of the Carbon atoms may have a different number of neutrons, these are called isotopes
The most common form of Carbon is Carbon-12 but it can
also exist as Carbon 14
Isotopes will have the same chemical properties
Different physical properties (e.g. density)
https://gcps.desire2learn.com/d2l/lor/viewer/viewFile.d2lfile/6605/48792/PeriodicTable/Ions_and_Isotopes/Ions_and_Isotopes_print.html
Radioisotopes
Isotopes = atom of an element with a different number of neutrons
The most abundant isotope of an element will be the stable isotopes
Radioisotopes = unstable isotopes which may spontaneously decay by emitting a particle (or waves of radiation) from the nucleus to become more stable
Radioactive elements (e.g. Uranium) have no stable isotope
Periodic table showing isotope abundance
From: http://commons.wikimedia.org/wiki/File:Periodic_Table_Radioactivity.svg
From: http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-structure-of-matter/the-nuclei-of-atoms-at-the-heart-of-matter/what-holds-nuclei-together/
Forces holding nuclei together
Uses of isotopes
Carbon-14 used in ‘carbon dating’ to determine the age of organic material. It can date objects up to 60 000 years old.
Americium-241 used in smoke detectors in your home to detect smoke.
Technetium-99 and Iodine-131 patients are given a radioisotope before going into certain scanners/imagers
The case of the radium watches
In the 1900’s Radium (a radioactive element) was widely used in glowing clock and watch hands
Young women who worked in the watch factories used to 'point' their brushes by licking and shaping the bristles prior to painting the fine lines and numbers on the dials. This practice resulted in the ingestion of radium, which caused serious health problems.
The Radium Girls, a group of young women working for US Radium in 1917, sued their employer for contracting an occupational disease. In the wake of the case, industrial safety standards were demonstrably enhanced for many decades.
Radium has a half life of 1600 years, so even today the old watch faces are still radioactive!
Resources - Isotopes
Further Reading Interactive periodic table http://www.ptable.com/ Periodic table of isotopes http://www.ciaaw.org/ How atomic particles helped solve a wine fraud
AV Tyler DeWitt - What Are Isotopes? (7:55) Khan Academy – Four Fundamental Forces Khan Academy – Nuclear stability and nuclear equations (8:24) SciShow - Strong Interaction: The Four Fundamental Forces of Physics #1a (3:36) SciShow - Strong Interaction: The Four Fundamental Forces of Physics #1b (3:52) SciShow - Electromagnetism - Electrostatic Force: The Four Fundamental Forces of Physics
#4a (3:37)
How did you go? Define:
Nucleus, proton, neutron, electron, atomic number, mass number, atomic mass unit
State the mass of protons, neutrons and electrons in terms of the atomic mass unit
Calculate the number of neutrons, electrons and protons in an atom by using the atomic number and mass number
Convert between atomic mass units and kilograms Give the SI unit for: masses on the atomic or molecular scale Define:
Isotope, radioisotope, nuclide, nucleon, strong nuclear force, electromagnetic force
Recall that a large number of isotopes exist for each element Identify that isotopes have different physical properties Identify that the mass number on the periodic table represents the most stable
isotope/s of an element Explain how the strong nuclear force opposes the electrostatic repulsion between
the protons in a nucleus Identify that most isotopes of elements are radioisotopes Identify that stable isotopes are the most abundant isotopes