-+Distinguishing+Among+Atoms

toc
= = =- Atomic number=
 * the number of protons
 * the whole number on the periodic table
 * determines identity of the atom
 * The 15 is the atomic number



http://www.youtube.com/watch?v=lDo78hPTlgk

=- Mas﻿s number=
 * The mass number is the number of protons plus the number of neutrons.
 * It is the rounded atomic mass number to the nearest whole number
 * The mass number will always be greater than the atomic number unless it is hydrogen

= =
 * 1) Example: Phosphorus's atomic mass number is 30.973762, so the mass number is 31
 * 2) Example: Tin’s atomic mass number is 118.710 so the mass number would be 119.

=- Isotopes=

Isotopes are atoms that have the same number of protons (and electrons) but they differ in the number of neutrons. Because they have different numbers of neutrons, they have different mass numbers.



=- Ions= Positive and negative ions form when electrons are transferred between atoms.

a) Cations- An Ion that loses electrons end up with a positive charge and is called a cation. The sign for a cation is written as a number followed by a plus sign. If the charge is 1 +, the the umber 1 is usually omitted from the symbol for the ion.



b) Anion- An ion that has gained electrons and therefor has a negative charge. The charge for an anion is written as a number followed by a minus sign.



= =

=- atomic mass=

Atomic mass is the weighted average of mass of the atoms (average mass of the element’s isotopes). The picture below shows where the atomic mass can be found on the periodic table: 

There are three things you need to know to calculate the atomic mass:
 * 1) NUMBER of __stable isotopes__ of the element
 * 2) MASS of each __isotope__
 * 3) NATURAL PERCENT __abundance__ of each isotope

Once you know these three facts, multiple the MASS (#2) of each isotope by its NATURAL ABUNDANCE (#3), expressed as a decimal (ex. 2.6% becomes 0.026) then add the products.

= = = =

=- periodic table (groups or families/ rows or periods)= A periodic table is an arrangement of elements in which the elements are separated into groups based on a set of repeating properties. A periodic table allows you to easily compare the properties of one element (or a group of elements) to another element (or group of elements). The elements are listed in order of increasing atomic number, from left to right. Each horizontal row of the periodic table is called a period or row, each element varies as you move across from it to the next one. There are seven periods in the modern periodic table. Each vertical column of the periodic table is called a group, or family. Elements within a group have similar chemical and physical properties. Each group is identified by a number and the letter A or B.

= = media type="youtube" key="GFIvXVMbII0" width="295" height="245"

=- radioactivity=

= =

** RADIOACTIVITY ** VIDEO: @http://www.youtube.com/watch?v=lFXUfK_C8jY&feature=related

** *R **** adioactivity is the spontaneous disintegration of atomic nuclei. ** *

=
Radioactivity refers to the particles, which are emitted from the nucleus as a result of nuclear instability. Because the nucleus experiences the intense conflict between the two strongest forces in nature, it should not be surprising that there are many nuclear isotopes which are unstable and emit some kind of radiation. The most common types of radiation are called alpha, beta, and gamma radiation, but there are several other varieties of radioactive decay. =====



=
Radioactive decay rates are normally stated in terms of their half-lives, and the half-life of a given nuclear species is related to its radiation risk. The different types of radioactivity lead to different decay paths, which transmute the nuclei into other chemical elements. Examining the amounts of the decay products makes possible radioactive dating. Radiation from nuclear sources is distributed equally in all directions, obeying the inverse square law. =====

=- Pierre and Marie Curie (radium, polonium)=

== - The Curies won the Nobel Prize in Physics in 1903. They received this award for their joint research on radiation. Their research further built upon Professor Becquerel's monumental discoveries on the subject. ==

- The "Curie" is a unit of radioactivity. It is unknown whether it was named after Pierre, Marie, or both.
=- Bequerel (uranium)= ** Antoine Henri Becquerel ** ** (1852-1908) **

** Henri Becquerel was born into a family of scientists **. His grandfather had made important contributions in the field of electrochemistry while his father had investigated the phenomena of fluorescence and phosphorescence. Becquerel not only inherited their **interest in science**, he also inherited the minerals and compounds studied by his father. And so, upon learning how Wilhelm Roentgen discovered X rays from the fluorescence they produced, Becquerel had a ready source of fluorescent materials with which to pursue his own investigations of these mysterious rays. The material Becquerel chose to work with was **potassium uranyl sulfate, K** ** 2 **** UO **** 2 **** (SO **** 4 **** ) **** 2 ****, ** which he exposed to sunlight and placed on photographic plates wrapped in black paper. When developed, the plates revealed an image of the uranium crystals. **Becquerel concluded, "that the phosphorescent substance in question emits radiation which penetrates paper opaque to light." Initially he believed that the sun's energy was being absorbed by the uranium, which then emitted X rays.** Further investigation, on the 26th and 27th of February, was delayed because the skies over Paris were overcast and the uranium-covered plates Becquerel intended to expose to the sun were returned to a drawer. **On the first of March, he developed the photographic plates expecting only faint images to appear. To his surprise, the images were clear and strong. This meant that the uranium emitted radiation without an external source of energy such as the sun. Becquerel had discovered radioactivity, the spontaneous emission of radiation by a material.**

Later, Becquerel demonstrated that the radiation emitted by uranium shared certain characteristics with X rays but, unlike X rays, could be deflected by a magnetic field and therefore must consist of charged particles. For his discovery of radioactivity, **Becquerel was awarded the 1903 Nobel Prize for physics.**

= ALPHA RADIATION! =

-cannot penetrate even the dead layer of human skin -alpha-emitting materials can be harmful to humans if injested, swallowed, or absorbed trhough open wounds. -it increases the risk of cancer, and in particular lung cancers in humans -alpha particles become helium after traveling a very short distance through the air (1/20 of the speed of light) -Ernest Rutherford, and english scientist. discovered the alpha particle while working with uranium in 1899 -alpha particles are identical to helium with two protons and two neutrons, a high energy particle, and a positive charge of +2 due to its protons

= = - this demonstrates an equation where an alpha particle is given off

- this diagram shows that alpha radiation wont even go through a thin piece of paper. therefor it is the least harmful of all radiations.

=- Beta radiation=