IONS and ISOTOPES

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IONS and ISOTOPES
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What are ions?

• An atom is neutral. It has neither a positive
  nor a
• negative charge. In order for an atom to be
  neutral,
• the number of electrons must equal the number of
• protons. The positive and negative charges
  cancel
• each other. If an atom does not have the same
• number of protons and electrons, an ion is
  formed.
• When an atom loses or gains one or more
  electrons,
• it acquires a net electrical charge and it is
  called an
• ion.

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EXAMPLE

• A neutral magnesium (Mg) atom has 12 protons and
• 12 electrons. If the magnesium atom loses 2
• electrons, it will have a net electrical charge
  of ?2.
•  
• To find net charge of an ion, subtract the number
  of
• electrons from the number of protons.
• Number of protons 12
•  
• - Number of electrons 10
  2
• A magnesium ion is represented as Mg2.

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EXAMPLE 1

• 1. Sodium (Na) atoms have ____ protons and
  ____electrons with a net charge of ______.
•   (11 11 0)
• 2. If the Sodium ion has only 10 electrons,
  what is the net charge of the ion? ________.
• (11 -10 1)
• 3. What is the chemical symbol for this ion?
  ______________

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EXAMPLE 2

• 1. Beryllium (Be) atoms have ____ protons and
  ____electrons with a net charge of ____.
• (4 4 0)
•  
• 2. If the Beryllium ion has only 2 electrons,
  what is the net charge of the ion? ______.
• (4 -2 2)
•  
• 3. What is the chemical symbol for this ion?
  ______________

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What are Isotopes?

• All atoms of an element have the same atomic
• number and the same number of protons. However,
• atoms do not necessarily have the same number of
• neutrons. Atoms with the same number of
  electrons
• and protons, but different numbers of neutrons,
  are
• called isotopes. Different isotopes belong to
  the
• same element because they have the same number of
• electrons, which means that they all behave
  almost
• the same in chemical reactions.

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Isotopes of Hydrogen

• Hydrogen 1
• Protons  1
• Electrons 1
• Neutrons 0
• Hydrogen 2
• Protons 1
• Electrons 1
• Neutrons 1
• Hydrogen 3
• Protons 1
• Electrons 1
• Neutrons 2

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Complete Nuclear Symbols

• Isotopes should be written using the complete
  nuclear symbol
• or by using a hyphen symbol. A charge should be
  indicated
• if the atom is not neutral. 
• EXAMPLE (hyphen symbol) Chlorine - 37 ? mass
  number 
• Complete nuclear symbol mass number
  37
• for an element is
  Cl 2 ? element symbol and charge
• written like this atomic
  number 17

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Practice Problems

• List out the number of protons, electrons, and
  neutrons of
• 207
• Pb
• 82

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• List out the number of protons, electrons, and
  neutrons of
• 55
• Mn 2
• 25

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• Atoms of a certain isotope have 73 neutrons and a
  mass of 123. 
• a. What is the atomic number?
•  
• b. How many electrons are there?
•  
• c. What is the name of the element?
•  
• d. Write the chemical symbol for this isotope.
•