atomic structure + bonding Flashcards
Bonding of ionic compounds
Ionic bonds are strong electrostatic forces of attraction between opposite charged ions
Structure of ionic compounds
Ions in an ionic compound form a lattice structure:
-regular arrangement of ions
-ionic bonds between oppositely charged ions
M.p and b.p of ionic compounds
High
Solid at room temperature:
-many strong ionic bonds
-large amounts of energy must be -transferred to break structure
What is the solubility of ionic compounds in water ?
Ionic compounds often soluble in water - dissolve to form aqueous solutions
What are ionic lattices referred to ?
Called ‘giant lattice’ as involves many ions
Where can covalent bonds occur (singular)
Covalent bonds occur in a single element - group number
Properties of covalent bonds NOT SIMPLE MOLECULAR SUBSTANCES
-strong
-between non metals
-produce molecules
Bonding of SIMPLE COVALENT SUBSTANCES
Simple molecule made up of few atoms joined by strong covalent bonds :
-non metal compounds (HCL,CH4)
-non-metal elements (H2, O2)
Usually have low mp and BP so liquid or gas at room temperature
Intermolecular forces / difference between them and covalent bonds
Weak attractive forces between molecules called intermolecular forces - when simple molecular substance melts or boils :
-intermolecular forces overcome
-covalent bonds do NOT break
Do simple molecular substances conduct ?
Do not conduct as - not electrically charged and do NOT contain electrons that are free to move
SOME however break down in a solution, forming ions that can move - solution can therefore conduct
Do simple molecular substances dissolve in water ?
MANY simple molecular structures insoluble in water - intermolecular forces between water and substances weaker than those between
-water molecules
-molecules of the substance
What are the conditions for solubility ? (Simple molecular structures)
Only of they can form strong enough intermolecular forces with water molecules e.g.
-hydrogen + water sparingly soluble
-chlorine, carbon dioxide, sulfur dioxide and ammonia soluble
-ethanol and ethanoic acid soluble
-sugar soluble in water
Example - explain why nitrogen is suitable for use as an insulator in high voltage electrical transformers
Unreactive - does not react with materials in transformer. Can insulate as does not conduct electricity
What is bonding and structure like in a giant molecular structure?
Giant molecules consists of many atoms :
-joined by strong covalent bonds
-arranged in a regular lattice structure
-Can be non metal elements e.g. carbon or compounds such as silicone
What is the melting and boiling points of giant molecular compounds ?
-High mp+bp so solids at room temp. Lots of energy transferred to break the MANY strong covalent bonds
What is the solubility of giant molecular substances ?
Insoluble in water
How do we represent giant molecular substances ?
Because there are many atiks you cannot represent an entire giant molecule using displayed formulae or dot and cross diagrams
Arrangement of diamond
-each atom bonded to four others
-strong covalent bonds between atoms
-hexagonal shape
-form of carbon
Arrangement of graphite
-Each atom bonded to 3 others
-weak intermolecular forces between layers
-strong covalent bonds between atoms in a layer
Uses of graphite
In graphite, the weak intermolecular forces let the layers slide over each other - useful as a lubricant + slippery
(WORKED EXAMPLE)
Graphite is used to make electrodes because it contains electricity. Explain why it conducts electricity but diamond does not ?
A carbon atom can form four covalent bonds - in graphite each carbon atom only forms 3 covalent bonds. The non binding outer electrons become delocalised meaning they can move through the structure, so graphite can conduct. Diamond does not have delocalised electrons so cannot conduct.
What is the structure of graphene / how is it represented ?
Graphene resembles a single later of graphite:
-each carbon atom is covalently bonded to three other carbon atoms
-it has a regular lattice structure
-interlocking hexagonal rings of carbon atoms
What are the properties of graphene ?
-conducts electricity because non bonding outer electrons become delocalised and can move through the structure
-is STRONG and FLEXIBLE as contains many strong covalent bonds
-is almost transparent as its layers are just one atom thick
What is a fullerine ?
Fullerenes resemble a sheet of graphene rolled
What are buckyballs ? (Fullerene)
Hollow balls.
Buckminsterfullerene has carbon atoms arranged in pentagons as well as hexagons.
Materials made from buckyballs :
-conduct electricity as have delocalised electrons
-are soft when solid because they have weak intermolecular forces
What are nanotubes ? (Fullerene)
Hollow tubes with open or closed ends. They can be several mm long.
-conduct as have delocalised electrons
-strong because the structure is made of many strong covalent bonds
Poly(ethane) misconception
Poly(ethane) is not a fullerene but a hydrocarbon. Polymer molecules describes as macromolecules rather than giant covalent structures
(WORKED EXAMPLE) describe the structure of poly(ethane)
Consists of large molecules containing chains of carbon atoms these atoms are joined together and to hydrogen atoms by covalent bonds.
Properties of metals (reshaping)
Malleable- bent into shape without shattering. If force applied layers of ions slide over each other changing the shape of the metal. whereas non metals brittle and will break when bent or hit in the solid state
Metallic bonding
Consists of a giant lattice of positively charged metal ions + has a sea of delocalised electrons - come from the outer shells of the atoms.
Metallic bonds are strong forces of attraction between positive metal ions and delocalised electrons
Solubility of metals
Insoluble in water, however some dissolve - react with water to produce soluble metal HYDROXIDES, (and hydrogen) which dissolve exposing more metal to the water.
How do we represent structure and bonding ?
The structure and bonding of different substances are represented using models. (All of which have some limitations)
Positives and Limitations of the written formulae
Empirical:
-simplest whole number ratio. This does not show how the atoms are arranged or the actual number of atoms
Molecular:
-number of atoms in an element. Does not show how the atoms are arranged
Structural:
-most accurate as gives example of number of atoms and how they are arranged.
Limitations of drawn structures
When you draw a structure you should show all the covalent bonds in a molecule
- does not show molecules three-dimensional shape
-does not show the bonding and non-bonding electrons
Positives and Limitations of ball and stick models
Can be drawn or modelled ✅
Do not show ❌
-how each atom is bonded to other atoms
-the molecules three dimensional shape
Do not show the bonding and non bonding electons, or each elements chemical symbol.
Positives and Limitations of space filling models
✅more accurate in showing sites if atoms relative to their binds than ball and stick
❌may not see all the atoms in q complex space filling model
(WORKED EXAMPLE) Positives and negatives of dot and cross diagrams
✅this diagram shows the symbol for each atom in the molecule. Shows how each atom is bonded to other atoms. Pair of electrons in each covalent bond shown by dots and crosses non bonding pairs of electrons in the outer shells are included.
❌does not show the three dimensional shape of the molecule. May lead you to think that the molecules are flat as two dimensional.
Why are covalent bonds strong ?
Covalent bonds are strong because the shared electrons are attracted to the nucleus of both atoms.
What is the advantage of double and triple bonds?
Double and triple bonds are normally stronger and require more energy to break.
