Download Sample Questions Sample Questions Standard Atomic Notation

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Sample Questions
For each of the following elements, state the number of protons, electrons and neutrons in one atom.
• Sodium
• Selenium
• Fluorine
• Helium
Nov 14­9:20 AM
Standard Atomic Notation
• Scientists use a special system to communicate information about any atom. • This system is known as the standard atomic notation
• This system represents the numbers of subatomic particles.
• Examples:
35CL 23Na
17 11
• The top number is the atomic mass and the bottom number is the atomic number.
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Organizing the Elements
November 14, 2011
Sample Questions
Element Protons Electrons Neutrons
Sodium 11 11 12 Selenium 34 34 45
Fluorine 9 9 10
Helium 2 2 2
Nov 14­9:20 AM
Standard Atomic Notation
• 35CL 35 is the atomic mass, 17 is the atomic 17 number. The number of protons is 17, the number of electrons is 17 and the number of neutrons is 18.
• 23Na 23 is the atomic mass, 11 is the atomic 11 number. The number of protons is 11, the number of electrons is 11 and the number of neutrons is 12.
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Organizing the Elements
• People often organize things to make them more useful.
• Other methods of organization were considered but later discarded.
• Up to the mid­1800s, scientists were busy discovering new elements.
• Then they tried to organize the elements alphabetically. But every time a new element was discovered, the whole list had to be changed.
• John Dalton then found a quantity that could be measured for an element ­ its atomic mass.
• Several scientists then tried to arrange the known elements by their atomic masses.
• The best arrangement was produced by a Russian scientist, Dmitri Mendeleev.
• Cupboards
• Closets
• Study notes for tests
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• State (gas, solid, liquid)
• Color
• Taste
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Untitled.notebook
Organizing the Elements
• Mendeleev began arranging the elements in order of increasing atomic mass and noticed that many elements shared common properties. These elements typically belonged to the same vertical column of his table.
• Mendeleev’s arrangement showed a regular pattern. Mendeleev’s periodic law states:
If the elements are arranged according to their atomic mass, a pattern can be seen in which similar properties occur regularly.
Nov 14­9:20 AM
November 14, 2011
Organizing the Elements
• Mendeleev’s periodic table was a major breakthrough in the understanding of the elements. However, it was discovered later on that using the atomic mass was not the proper way to organize the elements. • The key was to use the atomic number or the number of protons.
• Therefore, a new law was born.
• The modern periodic law states :
If the elements are arranged according to their atomic number, a pattern can be seen in which similar properties occur regularly.
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Groups of Elements
• The periodic table is useful since it organizes the elements according to similar properties.
• The set of elements in the same column in the table is called a chemical group and they share similar physical and chemical properties.
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