Bonding
- Created by: Rachel98
- Created on: 19-05-15 12:03
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- Bonding
- Ionic Bonding
- Ions are formed when one or more electrons are transferred from one atom to another.
- Electrostatic attraction holds positive and negative ions together
- These bonds are very strong
- When oppositely charged ions form and ionic bonds. A ionic compound is formed.
- The formula of an ionic compound tells you what is in the compound. The negative charges will always balance the positive charges
- So the compound has no overall charge
- Giant Ionic Lattice
- Ionic crystals are giant ionic lattices
- These are called giant because they are made up of the same basic unit repeated over and over again
- Different ionic compounds have different shaped structures, but they are all still giant lattices.
- Behaviour of ionic compounds
- Electrical Conductivity
- Ionic compounds only conduct electricity when they are either in solution or molten
- Ions in liquids are free to move so they can carry a current meaning that they can conduct electricity
- In a solid the ions are in a fixed position so they cannot move
- Solid ionic compounds do not conduct electricity
- Ionic compounds only conduct electricity when they are either in solution or molten
- Solid ionic compounds do not conduct electricity
- In a solid the ions are in a fixed position so they cannot move
- Melting point
- Ionic compounds have high melting points
- The giant ionic lattice is held together by strong electrostatic forces
- This means that a lot of energy is required to overcome these forces
- Resulting in high melting points for ionic compounds
- This means that a lot of energy is required to overcome these forces
- Solubility
- Ionic compounds tend to dissolve in water
- This is due to the polarity of water molecules
- The water molecules pull the ions away from the lattice. Causing it to dissolve
- This is due to the polarity of water molecules
- Ionic compounds tend to dissolve in water
- Electrical Conductivity
- Covalent Bonding
- Molecules
- Smallest part of the compound which can take part in chemical reactions.
- They are formed when two or more atoms bond together
- Molecules are held together by strong covalent bonds
- They are formed when two or more atoms bond together
- Smallest part of the compound which can take part in chemical reactions.
- Single bonds
- In covalent bonds, two atoms share electrons until they both have full outer energy levels
- In a single bond there is only one shared pair of electrons in each bond
- Double or triple bonds
- Where there are two or more shared pairs of electrons between two atoms
- Behaviour of simple covalent bonds
- Simple covalent compounds
- have strong bonds within the molecule but weak intermolecular forces between the molecules
- Their physical properties are determined by the bonding in the compound
- Electrical Conductivity
- Simple covalent compounds don't conduct electricity
- Because there are no free ions or electrons to carry the charge
- Simple covalent compounds don't conduct electricity
- Melting Point
- Simple covalent compounds have low melting points
- Because the weak intermolecular forces between molecules are easily broken
- Simple covalent compounds have low melting points
- Solubility
- Some simple covalent compounds dissolve in water depending on how polarised the molecules are
- Simple covalent compounds
- Molecules
- Giant Covalent Structures
- Graphite (Carbon)
- The carbon atoms in graphite are arranged in sheets of flat hexagons covalently bonded with 3 bonds each
- The fourth outer electron is delocalised.
- These delocalised electrons are free to move so allow a current to flow
- Graphite can conduct electricity
- These delocalised electrons are free to move so allow a current to flow
- The sheets of hexagons are bonded together by weak van der waals forces
- The layers are quite far apart compared to the length of the covalent bonds
- Graphite has a low density and so is used to make lightweight sports equipment
- The layers are quite far apart compared to the length of the covalent bonds
- The strong covalent bonds mean that graphite has a high melting point
- It sublimes at over 3900K
- Graphite is insoluble in any solvent as the covalent bonds are too strong to break
- The fourth outer electron is delocalised.
- The weak IMF can be easily broken so the sheets of carbon can slide over each other
- The carbon atoms in graphite are arranged in sheets of flat hexagons covalently bonded with 3 bonds each
- These have huge networks of covalently bonded atoms.
- Diamond (Carbon)
- Each carbon atom is covalently bonded to four other carbon atoms.
- It has a very high melting point
- Sublimes at over 3800K
- Diamond is insoluble in any solvent just like graphite
- It has a very high melting point
- The carbon atoms arrange themselves into a tetrahedral shape
- Crystal lattice
- It is very hard
- Used for tips of drills
- Good thermal conductor
- Vibrations travel easily through the stiff lattice
- Can't conduct electricity
- All electrons are held in bonds non are delocalised
- Each carbon atom is covalently bonded to four other carbon atoms.
- Graphite (Carbon)
- Dative Covalent Bond
- It is the same as an ordinary covalent bond but both shared electrons are provided by the same atom.
- There is one dative covalent bond in the ammonium ion
- Between the nitrogen atom and one of the hydrogen atoms
- Both of the electrons come from the nitrogen atom
- Intermolecular Forces
- Van der Waals
- The constantly moving electrons within charge clouds can induce a dipole on molecules close by.
- The two dipoles are attracted to each other
- Because the electrons are constantly moving, dipoles are constantly being created and distroyed
- Even though the dipoles keep changing, the overall effect is that the atoms are attracted to each other
- The stronger the intermolecular forces, the higher the boiling and melting point of a substance because more energy is needed to overcome them
- Not all Van der Waals forces are the same strength
- Larger molecules have larger electron clouds so have stronger forces.
- Molecules with a larger surface area also have stronger forces
- There is a bigger area for the forces to act upon
- More exposure of the electron cloud
- Molecules with a larger surface area also have stronger forces
- Larger molecules have larger electron clouds so have stronger forces.
- The constantly moving electrons within charge clouds can induce a dipole on molecules close by.
- Permanent dipole- dipole forces
- The charges on polar molecules cause weak electrostatic forces of attraction between molecules
- If you put a charged rod next to a polar liquid such as water, the liquid will move towards he rod due to the permanent dipoles within the liquid
- This will happen if the rod is positively or negatively charged as the polar molecules in the liquid can turn around so that they are attracted to the rod
- If you put a charged rod next to a polar liquid such as water, the liquid will move towards he rod due to the permanent dipoles within the liquid
- The charges on polar molecules cause weak electrostatic forces of attraction between molecules
- Hydrogen bonding
- The strongest intermolecular force
- Only occurs when hydrogen is covalently bonded to fluorine, nitrogen or oxygen
- These are all very electronegative, so they draw the bonding electrons away from hydrogen.
- These bonds are so polar that hydrogen can then bond with the lone pair of electrons on another molecule
- These are all very electronegative, so they draw the bonding electrons away from hydrogen.
- Only occurs when hydrogen is covalently bonded to fluorine, nitrogen or oxygen
- The strongest intermolecular force
- Van der Waals
- Ionic Bonding
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