Definitions of Elements
- An element is a pure substance that cannot be broken down by chemical means.
- Elements are defined by the number of protons they possess; that is, all atoms of an element have the same atomic number.
- Elements contain only one type of atom.
Each of the known elements is given a name and a one- or two-letter abbreviation (symbol). Often this abbreviation is simply the first letter of the element; for example, hydrogen is abbreviated as H, and oxygen as O. Sometimes an element is given a two-letter abbreviation; for example, helium is He. <ref>Matter: Atoms from Democritus to Dalton by Anthony Carpi, Ph.D.</ref> Exceptions to this are newer unnamed elements; for example, elements between 111 and 119 are given three letter designations. <ref>Emsley, J. (2002). Nature's Building Blocks: An A-Z Guide to the Elements. Oxford University Press.</ref>
Rules of Element Symbols
- The first 1-2 distinguishing letters in the element's name is used for the symbol
- The first letter is uppercase; the second letter is always lowercase
Learning the Elements
Memorization is an important step to understanding chemistry, however, memorizing every known element is not necessary. Instead, beginning chemists should start memorizing the first 20 elements, representative elements, and elements derived from ancient names. The remaining elements may be found by looking on a periodic table.
Symbols from Ancient Names
Students should memorize all the symbols derived from ancient names:
|English name||symbol||ancient name|
The First 20 Elements
Happy Henry, the Little Beach Boy, CaN dO FiNe.
Naughty Meghan, the Alpine Sister, Pretends to Ski at ClArK Canyon.
The Element Song
Tom Lehrer provided the chemistry community with a fun way of thinking about the known elements by singing the names of the elements to the tune of I Am the Very Model of a Modern Major General from the musical Pirates of Penzance.
Table of Elements
|Element name||Neon-20||The element name is followed by the mass number (A).|
|Element symbol||21Ne||Element symbol with the mass number to the left as a superscript|
|Isotopic notation||21Ne||Element symbol with the mass number to the left as a superscript and the atomic number as a subscript.|
1. To learn about the terms isotopes, atomic number, and mass number.
2. To understand the use of the symbol AZX to describe a given atom.
3. To learn about various features of the periodic table.
|Carbon has radioactive isotopes. Yes – you are radioactive.<ref name="Stealthpaw">Stealthpaw, J. (January 09, 2009). Fun Facts about Nukes and Radiation. Retrieved January 30, 2009. http://jaspian.livejournal.com/20841.html </ref>
Tritium is the substance we associate with radiation. It has a short halflife, and has an eerie luminescent greenish glow. Most radioactive substances do not glow, and are not green. For example, raw uranium is yellow. Refined, it is a dull metallic gray.<ref name="Stealthpaw" />
The scientist who discovered what radiation is was a woman: Marie Curie. Unfortunately she died of radiation poisoning after years of experimentation with it.<ref name="Stealthpaw" />
Uranium isn’t very radioactive. The radioactivity of an isotope is typically inversely proportional to its halflife.<ref name="Stealthpaw" />
Only a very small amount of an atom’s mass is converted into energy during fission.<ref name="Stealthpaw" />
Dalton and Isotopes
Dalton’s theory tended to revolve around a way to describe the masses of isotopes. The existence of isotopes didn't affect any development because isotopes of a given element have virtually identical chemical properties and they all don’t change chemical reactions. Also, the relative proportions of isotopes are constant, regardless of where they are, and no matter how big or small they may be.
Helium and Isotopes
Isotopes have a fixed number of protons, but many exist with various numbers of neutrons. The sum of the protons and neutrons is known as the mass number. An example of an element with two different masses is helium. It can be 3He with two protons and one neutron or 4He with two protons and two neutrons, and these would be known as the isotopes of Helium. Isotopes can have the same chemical properties, but their weights vary. Something interesting about isotopes is the amount of time it takes for half the atom to decay into a more stable form, also known as half-life. There is naturally an abundant amount of isotopes that exist around us because their half-lives are longer than the age of the earth!
There are different ways an isotope can decay. They can do this by beta decay, which is emitting an electron and converting a proton into a neutron. B-decay is emitting a positron anti-electron and converting a proton to a neutron. B+ decay is capturing an atomic electron and converting a proton to a neutron is also known as electron capture decay. Also other isotopes can decay by alpha decay. Alpha decay emits an alpha particle which is really a 4He nucleus. Heavy elements occasionally decay by spontaneous fission, dividing the electron in half. An isotope can decay in several possible ways, often emitting gamma-rays as loose energy. Isotopes can act differently when compared to different forms of radiation.
Hydrogen & Isotopes
To distinguish the isotopes of elements such as Hydrogen, you have to look at the number of neutrons. For example, the three isotopes of hydrogen are hydrogen, deuterium, and tritium. Hydrogen has no neutrons, deuterium has one neutron, and tritium has two neutrons. They all have one proton because protons and neutrons interact making the chemical properties the same.
Isotopes Chemical Properties
Isotopes chemical properties are identical, but have great differences when it comes to nuclear stability. The number of neutrons will be most equal to the number of protons, but a growing neutron is a characteristic of stable heavy elements. The element Tin has the most stable isotopes with ten, and the average is usually 2.6 stable isotopes for each element. Another thing about isotopes is that the atomic masses are rarely even numbers. Some modern uses for isotopes are smoke detections which use Americium-241. Radioisotopes can be used to help understand chemical and biological processes in plants.
You can find the numbers of neutrons, protons, and electrons in an isotope by simply using isotopic notation. A over Z to the left of X is the formula. The letter A represents the Atomic Mass, or the combined total of protons and neutrons. Z is the atomic number, or the number of protons and electrons in a given atom. Knowing what at least one is will end up giving you the other. Finally, X stands for the Element Symbol, or the actual symbol of the element being used. If the number of neutrons is given, you can determine the atomic mass. You have to add the atomic number to the number of neutrons to get the atomic mass.
www.chem4kids.com/files/atom_isotopes.html, http://www.colorado.edu/physics/2000/isotopes/index.html, http://hyperphysics.phy-astr.gsu.edu/hbase/HFrame.html, http://www.chem.duke.edu/~sds/cruise_ch/nuclear/uses.html
Original Drawing / Diagram
A X Z
1. Isotopes can be viewed as different versions of atoms, based on different numbers of neutrons.
2. Isotopes are atoms of the same element with different masses caused by differing numbers of neutrons.
1. 8 N A 14 6 + 8 = 14 C C 6 6
2. 12 N 24 24 24 – 12 = 12 Mg Mg Z 12
3. ? N 64 64 – 29 = 35 Cu 35 N 29
4. 8 N A 16 8 + 8 = 16 O O 8 8
5. What sub-atomic particle varies in isotopes? A. Neutrons
State Released Test Question
a. What are isotopes?
b. Isotopes are versions of atoms with different numbers of electrons. c. Isotopes are stagnant atoms with no charge. d. Isotopes are different versions of atoms with different numbers of neutrons. e. Isotopes are radioactive atoms with little charge. A. Isotopes are different versions of atoms with different numbers of neutrons.
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