Atoms, Bonding and the Periodic Table
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This section draws together ideas from many sections of the syllabus
and develops further the Peridoic Table to give an indication of the
ways chemists use theories to rationalise their knowledge. Ideas are
developed about atoms, molecules and ions by consideration of their
electronic structure.
The group number is related to the number of electrons in the outer shell. e.g. (Mg) Magnesium, in group 'II', has two electrons in the outer shell
- electrons are arranged in shells surrounding the nucleus, with the first shell containing 2 electrons and subsequently 8.
All atoms want a full outer shell of 8 electrons (like noble gasses)
Ionic Bonding:
- Ions are formed by gaining or loosing electrons
- is the transfer of electrons from one atom to another, giving the atom a positive of negative charge
- The two atoms together have a neutral charge
- It occurs mainly when metals bond with non-metals
Examples
Magnesium + Oxygen
Electron Configuration
- Mg: 2 --> transfer two electrons from Mg to give both atoms a stable electron configuration
- O: 2,6
Properties of Ionic Compounds
- solids at room temperature (strong bonds, opposite charges)
- high melting and boiling point (lots of energy required to overcome strong bonds)
- don't conduct electrivity in the solid state, since electrons can't move (can in the molten state)
- form crystaline solids because of ionic lattice
- dissolve readily in water, but not in molecular solvents
Covalent Bonding
- occurs when non-metals bond.
- They share electrons to get a noble gas structure
Example: Hydrochloric Acid (HCl)
- both H and Cl need one electron.
- They form a single covalent bond to get a full outer shell
Properties of Covalent Compounds
- molecules have no charge
- low melting and boiling points. (little attraction between molecules,)
- dont attract electricity (don't have charged particles)
- liquids of gasses at room temperature
- dissolve readily in molecular solvents, but not in polar solvents like water
Isotopes
- are atoms of the sama element with:
- same number of protons
- same number of electrons
- different number of neutrons
Examples
126C (6 electrons, 6 protons, 6 neutrons[12-6])
and
146C (6 electrons, 6 protons, 8 neutrons [14-6])
note: top number is the atomic mass
Relative Atomic Mass
-
average mass of atom
-
based on various isotopes present
Noble Gasses
-
unreative (inert)
-
because of full outer shell of electrons
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by: Admin
Total views: 2990
Word Count: 1038
Date: Sun, 21 May 2006 Time: 12:00 AM
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