OCR AS Chemistry F332: Ions and the Periodic Table

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Ions and the Periodic Table
Ions are formed when electrons are transferred from one atom to another.
Predicting Ionic Charges
You can predict the charge of an element's ion from its position on the periodic table.
You can find the number of electrons in the outer shell from the element's position in the
periodic table.
It is then a simple step to calculate how many electrons need to be lost or gained in order to
reach a noble gas configuration.
From this, you can predict the likely charge on the resulting ion.
For example:
Lithium in group 1 has one electron in its outer shell
To form the electron configuration of the nearest noble gas, helium:
A lithium atom must lose one outer electron
A lithium ion, Li+, therefore has a charge of +1
Elements in the same group of the periodic table have the same number of outer electrons
and react in similar ways.
Atoms of metals in Groups 1-3
Lose electrons
Form positive ions with the electron configuration of the previous noble gas in the
periodic table
Atoms of non-metals in Groups 5-7
Gain electrons
Form negative ions with the electron configuration
Atoms of Be, B, C and Si:
Do not normally form ons
Too much energy is needed to transfer the outer-shell electrons to form ions

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Group Elements Ion formed
Group 1 +1
Group 2 +2
Group 6 -2
Group 7 -1
Positive ions +1 Negative ions -1
(cations) (anions)
H+ Hydrogen Fl- Fluoride
Li+ Lithium Cl- Chloride
Na+ Sodium Br- Bromide
K+ Potassium I- Iodide
Cu+ Copper l OH- Hydroxide
Ag+ Silver NO3- Nitrate V or nitrate
NH4+ Ammonium NO2- Nitrate lll or nitrite
HCO3- Hydrogencarbonate
Positive ions +2 HSO4- hydrogensulfate
Mg2+ Magnesium Negative ions -2
Ca2+ Calcium (anions)
Sr2+ Strontium O2- Oxide
Ba2+ Barium S2- Sulfide
Fe2+ Iron…read more


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