Atoms and Ions

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Atoms and Ions

• SNC2D

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The Bohr-Rutherford Model

• Helium Atom
• 2 positive protons in nucleus
• 2 neutral neutrons in nucleus
• 2 negatively charged electrons in the first
  energy level

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Standard Atomic Notation(for a neutral atom)
Atomic symbol
Mass number
Br
80
35
Number of protons Atomic number (35) 35 p
Number of electrons (for neutral atom) Atomic number (35) 35 e-
Number of neutrons Mass number Atomic number (80-3545) 45 n0
Atomic number
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Neutral Atoms and Ions

• When using standard atomic notation you can
  assume the atom is neutral and the number of
  electrons is equal to the number of protons
• A charge is shown if it is an ion.

Br
80
1
Ionic charge (1 extra electron)
35
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Terms to Know

• Valence
• The combining capacity of an element
• Valence shell
• The outer electron shell of an atom, the
  electrons in this shell are called valence
  electrons
• Isoelectric with a noble gas
• The same number of electrons as a noble gas

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The Why of Ions

• The Noble Gases do not react and do not form ions
  because they already have what all atoms want
  full outer shells.

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Ions

• Many elements want to form stable ions where the
  number of electrons in the valence shell is the
  same as a noble gas.
• Metals tend to become positively charged cations.
• Non-metals tend to become negatively charged
  anions.
• They become ions by gaining or losing electrons
  (which ever is easier).

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Cations
1
Na
Na

• Easier to lose 1 electron than gain 7.
• Therefore the atom becomes a cation by losing an
  electron.
• It becomes more stable by losing an electron. It
  becomes iso-electric with Ne.

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Anions
1-
Cl
Cl

• Easier to gain 1 electron than lose 7.
• Therefore the atom becomes an anion by gaining an
  electron.
• It becomes more stable by gaining an electron. It
  becomes iso-electric with Ar.

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Anions

• The elements that form negatively-charged ions
  are non-metals.
• Non-metals, when they form ions, change their
  names to
• the first syllable the suffix ide

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Anion names

• chlorine
• fluorine
• bromine
• oxygen
• sulphur
• nitrogen
• phosphorus

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Valence Practice

• Given the following Bohr diagram, what will the
  valence of the ion be?

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Try These.

• Name the following ions K
• Mg2 b) O2- c) Br- d) N3-
• Suppose that a new element has been made.
  Chemical tests show that it is an alkaline earth
  metal. I
• Predict how many electrons will be in the outer
  orbit.
• Predict the ionic charge of the ion that this
  element forms.
• Justify why these ions do not exist under normal
  conditions. A
• K2 b) O-

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Credits

• http//mr.fusco.ca
• http//commons.wikimedia.org/wiki/FileHelium-Bohr
  .svg