Bonding, structure and the properties of matter Flashcards
What is ionic bonding?
Ionic bonding is the electrostatic attraction between positive and negative ions. It is a relatively strong attraction.
How are ionic compounds held together?
- They are held together in a giant lattice.
- It is a regular structure that extends in all directions in a substance.
- Electrostatic attraction between positive and negative ions holds the structure together.
State properties of ionic substances
- High melting point (strong electrostatic forces between oppositely charged ions).
- Do not conduct electricity when solid (ions in fixed positions).
- Conduct electricity when molten or dissolved in water - ions are free to move.
Give 5 examples of positive and 5 examples of negative ions. What is important when working out a formula of an ionic compound?
Positive: Na⁺, Mg²⁺, Al³⁺, Ca²⁺, Rb⁺
Negative: Cl⁻, Br⁻, SO₄²⁻, NO₃⁻, OH⁻ (chloride, bromide, sulfate, nitrate, hydroxide).
Ionic compounds are electrically neutral, therefore positive and negative charges must balance with each other.
How are ionic compounds formed? Explain in terms of MgO case
Happens with a metal and a non-metal.
Electron transfer occurs - metal gives away its outer shell electrons to give a non-metal.
Mg is is group 2, so have 2 available outer shell electrons.
O is in group 6, so can accept 2 electrons to get a full outer shell.
Mg becomes Mg²⁺ and O becomes O²⁻ (oxide).
What is a covalent bond?
Covalent bond is a shared pair of electrons between 2 non-metal atoms. Electrostatic attraction between shared pair of negatively charged electrons and positive nuclei holds it together.
Describe the structure and properties of simple molecular covalent substances
- Do not conduct electricity (no ions and no free electrons).
- Simple molecules.
- Weak intermolecular forces
- Low melting and boiling points.
How do intermolecular forces change as the mass/size of the molecule increases?
They increase. This causes the melting/boiling points to increase as well (more energy will be needed to overcome these forces).
What are polymers? What are thermosoftening polymers?
Polymers are very large molecules (>100, 1000s of atoms) with atoms linked by covalent bonds. The atoms in the polymer molecules are linked to other atoms by strong covalent bonds. The intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature.
Thermosoftening polymers - special type of polymers; they melt/soften when heated. The atoms are held together by strong covalent bonds. Large molecules which have weak intermolecular forces between chains which are easily overcome when heated.
What are the properties giant covalent substances? Give examples
- Solids (at room temperature), atoms covalently bonded in a giant lattice
- High melting/boiling points - strong covalent bonds.
- Mostly don’t conduct electricity (no delocalised electrons).
Examples include diamond, graphite and silicon dioxide.
Describe and explain the properties of allotropes of carbon
Diamond:
- Four, strong covalent bonds for each carbon atom.
- Very hard (strong covalent bonds).
- Very high melting point (strong covalent bonds).
- Does not conduct electricity (no delocalised electrons).
Graphite:
- 3 covalent bonds for each carbon atom.
- Layers of hexagonal rings.
- High melting point.
- Layers free to slide as weak intermolecular forces between layers; making it soft and used as a lubricant.
- Conduct thermal and electricity due to one delocalised electron per carbon atom.
Fullerenes:
- Hollow shapes molecules.
- Based on hexagonal rings but may have 5 or 7 rings.
- C₆₀ has spherical shape, simple molecular structure (Buckminsterfullerene). It is joined together by strong covalent bonds, but it has weak intermolecular forces, so is slippery and low m.p and b.p.
Nanotubes:
- Cylindrical fullerenes with high length to diameter ratio.
- High tensile strength (strong bonds).
- Electrical conductivity (delocalised electrons).
Graphene:
- A single layer of graphite.
- Very strong.
- Conduct electricity.
- Vey strong boiling/melting point.
What is metallic bonding?
Strong attractive bonds between delocalised electrons and nuclei of positive metal ions. A giant lattice structure.
Describe properties of metals
- High melting/boiling points (strong forces of attraction).
- Good conductors of heat and electricity (delocalised electrons).
- Malleable, soft layers of atoms can slide over each other whilst maintaining the attraction forces).
What are alloys? Why are they harder than pure metals?
Alloys are mixtures of metals with other elements usually metals.
Different sizes of atoms distorts the layers, so they can’t slide over each other, therefore alloys are harder than pure metals.
Different type of bonds
Simple covalent bonding:
Boiling and melting points: low because of weak intermolecular forces between molecules.
Conductivity when solid: poor, no ions to conduct electricity.
Conductivity when molten: poor, no ions.
General description, mostly gases and liquids.
Ionic bonding:
Boiling and melting points: high because of a giant lattice of ions with strong forces between oppositely charged ions.
Conductivity when solid: poor, as ions cannot flow.
Conductivity when molten: good, ions are free to move
General description: crystalline solids.
Giant covalent bonding:
Boiling and melting points: high because of many strong covalent bonds between atoms in a giant structure.
Conductivity when solid: diamond and sand - poor because electrons cannot move. Graphite - good as free delocalised electrons between layers can move through structure.
Conductivity when molten: poor.
General description: solids.
Metallic bonding:
Boiling and melting points: high because of strong electrostatic forces between positive ions and delocalised electrons.
Conductivity when solid: good as delocalised electrons are free to move through structure.
Conductivity when molten: good.
General description: shiny metal solids.
