School Science Lessons
Table 2. Table of the elements
Please send comments to: J.Elfick@uq.edu.au
Terms applied to the Table of
Actinides, actinoids: 2.1.0
Atomic mass units, amu: 2.4.0
Atomic number and mass number: 2.2.0
Atomic weight: 2.3.0
Free element metals: 2.6.0
Heavy metals: 2.7.0
Radiation, ionizing radiation, Geiger counter: 2.9.0
Radioactive carbon dating: 2.10.1
Radioactive elements: 2.10.0
Rare earth elements, lanthanides: 2.11.0
Symbol of an element: 2.12.0
Table 1. Periodic Table
Table of the elements
2.1.0 Actinides, actinoids
Actinoids, rare earth elements, from 89 Ac, to 103 Lr inclusive, are
metals shown separately below the main table, in period P7a.
Actinides can be represented by Ac. The valence of their cations varies.
They are all radioactive. They form part of the group of
Actinium | Thorium | Protactinium | Uranium | Neptunium | Plutonium | Americium | Curium | Berkelium
| Californium | Einsteinium |
a href="#FmS">Fermium | Mendelevium | Nobelium | Lawrencium
2.2.0 Atomic number and mass
Atomic number, Z, is the number of protons in the nucleus of an atom
of an element.
Mass number, A, atomic mass number, nucleon number, is the total number
of protons and neutrons in the nucleus of an atom of an
Atomic number is shown in the left subscript position and mass number
is shown in the left superscript position
See diagram 2.2.0: Carbon-12, Uranium-238,
2.3.0 Atomic weight
Atomic weight, relative atomic mass (r.a.m.), of an element, is the
ratio of the average atomic mass of an atom of an element,
including the common isotopes, to 1/12 the mass of an atom of carbon-12,
the unified atomic mass unit.
Awt, Atomic weight - elements
with no stable isotopes
Chlorine is 75% chlorine-35 and 25% chlorine-37, r.a.m. = 35.4527,
so atomic weight is usually quoted as 35.5.
For atomic weight values listed for elements with no stable isotopes.
See IUPAC Periodic Table of the Elements, 2011-01-21.
2.4.0 Atomic mass units, amu
Atomic mass units (u) are used to state the mass of an individual particle,
e.g. 1 atom of oxygen has a mass of 16.00 u.
The atomic mass unit is 1/12 of the mass of 12C. Mass of
1 amu = 1.66 × 10−27 kg
Elements, chemical elements, are substances that cannot be separated
into simpler substances.
All matter consists of single elements or combinations of elements.
The periodic table includes 92 naturally occurring elements and 8 or
more radioactive elements synthesized by nuclear reactions.
2.6.0 Free element metals
Free element metals are found in free elemental form, e.g. Gold | Copper.
2.7.0 Heavy metals
3.10.0 Poisons and First Aid (Table)
Heavy metals, a metal of relatively high density, specific gravity
> 5, metal of high relative atomic weight, especially if poisonous.
The term "heavy metals" has been used in legislation related to chemical
hazards and the safe use of chemicals with the legal regulations
in specifying a list of heavy metals to which they apply.
Heavy metals defined as elements commonly used in industry and generically
toxic to animals and to aerobic and anaerobic processes
may include As, Cd, Cr, Cu, Pb, Hg, Ni, Se, Zn.
So Copper | Lead | Mercury | Zinc, are called "heavy metals",
if they cause pollution.
The term "heavy metal" is not exact.
For example, although Aluminium and Beryllium are toxic, they are not
called heavy metals.
Metalloids have properties between metals and non-metals.
The metalloids are as follows:
| Boron | Silicon | Germanium | Arsenic | Antimony
| Tellurium |
Also some chemists include | Polonium | and | Astatine. |
2.9.0 Radiation, ionizing radiation,
See: Geiger Counters (Commercial)
See diagram 2.9: Geiger counter
Alpha particles have two protons and two neutrons, Helium nucleus
Beta particles are electrons.
Gamma rays and X-rays are pure photons.
A Geiger counter is used to detect alpha particles, beta particles
and gamma rays.
A radionuclide (radioisotope, isotope), emits radioactivity, gamma
rays and may be used in nuclear medicine.
The five types of ionizing radiation
1. Alpha radiation, α radiation + alpha particle
Uranium -238 --> thorium-234
238U92 --> 234Th90 +
4He2 + energy
An alpha particle can be shown as 4He2 or
uranium-238 --> thorium-234 + alpha particle + gamma rays (gamma
Uranium, symbol U, atomic number 92, is in group 6, period P7a of the
Alpha radiation travels a very short distance through air, cannot penetrate
skin or clothing, but it can be harmful if alpha-emitting
materials inhaled, swallowed, or absorbed through open wounds.
Transuranic elements, have atomic number > 92
2. Beta radiation, β radiation
Carbon-14 --> nitrogen-14 + beta particle + antineutrino
14C6 --> 14N7 + 0β-1
+ electron antineutrino ( ̅νe) + energy
Some useful Beta emitters:
3. Gamma radiation, γ radiation
Iodine-131 --> xenon 131 + gamma ray + beta particle
131I53 --> 131Xe54 +
0β-1 + 0γ0
The three most useful gamma radionuclides are:
4. X-rays: 27.23
5. Ultraviolet rays, Ultraviolet radiation (UV):
Ionizing radiation only wavelengths < 200 nm (called Vacuum UV
or VUV), occurs in the atmosphere
Absorbed dose of ionizing radiation = energy absorbed / mass of tissue
= J / kg, Grays (Gy)
Dose equivalent = absorbed dose × quality factor, Sieverts (Sv).
Quality factor is the comparative ionizing effect of radiation
Alpha particles 20,
Neutrons >10 k3V 10 (only from nuclear reactions or neutron bombs),
Beta particles 1, Gamma rays 1, X-rays 1.
Background radiation comes from space radiation,
e.g. cosmic rays at high altitude, terrestrial radiation,
e.g. radon-220, ingested thorium, potassium-40, manufactured radiation,
coal power stations, medical treatment,
2.10.0 Radioactive element,
stable isotope, half life
Nuclear, Geiger Counter, (Commercial)
Half-life from change in number of radioactive atoms - Equipment for senior physics practicals
By Todd Helmenstine
Technetium Tc-91, 4.21 x 106 years
Promethium Pm-145, 17.4 years
Polonium Po-209, 102 years
Astatine At-210, 8.1 hours
Radon Rn-222, 3.82 days
Francium Fr-223, 22 minutes
Radium Ra-226, 1600 years
Actinium Ac-227, 21.77 years
Thorium Th-229, 7.54 x 104 years
Protactinium Pa-231, 3.28 x 104 years
Uranium U-236, 2.34 x 107 years
Neptunium Np-237, 2.14 x 106 years
Plutonium Pu-244, 8.00 x 107 years
Americium Am-243, 7370 years
Curium Cm-247, 1.56 x 107 years
Berkelium Bk-247, 1380 years
Californium Cf-251, 898 years
Einsteinium Es-252, 471.7 days
Fermium Fm-257, 100.5 days
Mendelevium Md-258, 51.5 days
Nobelium No-259, 58 minutes
Lawrencium Lr-262, 4 hours
Rutherfordium Rf-265, 13 hours
Dubnium Db-268, 32 hours
Seaborgium Sg-271, 2.4 minutes
Bohrium Bh-267, 17 seconds
Hassium Hs-269, 9.7 seconds
Meitnerium Mt-276, 0.72 seconds
Darmstadtium Ds-281, 11.1 seconds
Roentgenium Rg-281, 26 seconds
Copernicium Cn-285, 29 seconds
Ununtrium Uut-284, 0.48 seconds
Flerovium Fl-289, 2.65 seconds
Ununpentium Uup-289, 87 milliseconds
Livermorium Lv-293, 61 milliseconds
2.10.1 Radioactive carbon dating
The radioactive isotope of carbon 14C has half-life 5700
The most abundant carbon isotope is 12C and ratio of 12C
/ 14C in the environment is constant enough in the environment
and so in the
tissues of living organisms.
At the death of an organism the amount of 14C decays exponentially,
so the age of a fossil organism can be estimated by comparing
its 12C / 14C ratio with the current value.
No carbon dating can be done for after 1950 because of contamination
of the atmosphere by nuclear explosions.
2.11.0 Rare earth elements,
Lanthanides rare earth elements (rare
earth metals), atomic numbers 57 La * to 71 Lu, are 15 metals shown separately
below in the
Periodic table, period P6a.
They are all named after where they were originally found in Sweden.
The "rare earths" are not "rare"!
If Lanthanides are represented by Ln, they all form trivalent cations
Lanthanum | Cerium | Praseodymium | Neodymium
| Promethium | Samarium | Europium | Gadolinium | Terbium | Dysprosium |
| Holmium | Erbium | Thulium | Ytterbium | Lutetium
The IUPAC adds Scandium, Sc, and Yttrium, Y, to the list of rare earth
elements because they have similar chemical properties and
are often found in the same ores as the lanthanides.
Scandium | Yttrium
2.12.0 Symbol of an element
Symbol of an element, e.g. H for Hydrogen.
Atomic symbols, chemical formula notation, e.g. Ac, were mainly invented
by the Swedish chemist Jacob Berzelius (1779-1848).