Year 11 Chemistry Lewis Structure and electron dot diagrams
Method for determining covalent bonding diagram
1. Count number of valence e- in the atom 2. Count number of electrons needed for full outer shell 3. Subtract the two numbers 4. Divide by 2 5. That's number of bonding pairs 6. Determine central atom (normally one where there is only one present) 7. It doesn't matter which is a double bond because this is just a representation of the quantum system 8. Hydrogen and oxygen are never central atom. 9. Then it is one furthest to left of the periodic table that is central,. 10. Hydrogen always bonded to oxygen and does not connect to central atom.
Valency
Ability of atom to combine with other atoms. Ddepends on number of valence electrons.
Graphite bonding
Each carbon atom bonded to 3 other carbons - strong covalent bonds Fourth electron delocalised and free to move between layers holding them together by weak forces of attraction layers referred to as graphenes Conductor due to delocalised electron Soft substance; layers can sheer off as they are only held together by weak force of electrostatic attraction High MP and BP.
Diamond bond
Each carbon bonded to 4 other carbons - strong covalent bonds Non conductor hard and brittle - each atom bonded to 4 others. Shatters when hit. High melting and boiling points
VSEPR (Valence shell electron propulsion/repulsion)
Lone pairs take up more space, only bordered by one atom Bonding atoms are being attracted by 2 atoms taking up less space Ask: How many electron clouds round CENTRAL ATOM. Lone pairs on non-central atoms unimportant
Electron dot diagram ionic compounds
Positive ion (cation): valence e- lost, empty outer shell. Negative ion (anion): valence e- gained, full outer shell. Brackets show they are ions.
Electron dot diagram covalent bonds
Share a pair of electrons with another atom. Can be displayed as - .
Lewis structure
Valence electrons represented by dots or crosses. Inner shells not shown.
nano-technology
nanoparticles are particles of 1-100 nanometers (10 to the -9 m). properties often differ from bulk materials due to small - quantum effects
