Structure and Bonding Flashcards
Ionic bonds
Metals transfer electrons to a non-metal to achieve a full outer shell. There are strong electrostatic forces of attraction between oppositely charged ions
Common ion formulas + charges
Ammonium - NH4+
Hydroxide - OH-
Carbonate - CO32-
Nitrate - NO3-
Sulfate - SO42-
Chloride - Cl-
Ions in ionic bonds
Metals lost electrons to form cations (e.g. Li+)
Non-metals gain electrons to form anions (e.g. Cl-)
Melting + boiling points of ionic structures
- Solids at room temperature
- Melting + boiling are state changes
- High melting + boiling points because ionic bonds have strong electrostatic forces of attraction between ions
Electrical conductivity of ionic structures
- Conduct electricity only when molten to form a liquid or dissolved in water to form an aqueous solution
- Both processes make ions free to move and conduct electricity
Covalent bonds
Strong electrostatic forces of attraction between the shared pair of electrons and nuclei of both atoms. It involves non-metals only.
Simple covalent structures
H2O, water
O2, oxygen
HCl, hydrogen chloride
CH4, methane
NH3, ammonia
CO2, carbon dioxide
Melting + boiling points of simple covalent structures
- Low melting and boiling points because the attractions between molecules are weak and easy to overcome. *Covalent bonds are NOT broken
Electrical conductivity of simple covalent structures
- Simple covalent molecules have no free ions or electrons
- They cannot conduct electricity (insulators)
Other properties of simple covalent structures
- Volatile (vaporises easily)
- Most are not soluble in water, but may dissolve in other solvents (e.g. cyclohexane)
Giant covalent structures
A 3D structure of atoms joined by covalent bonds (e.g. diamond, graphite, fullerene)
Giant covalent structure examples
- Graphite, diamond, and fullerene are all allotropes of carbon in solid form
- Carbon can form up to 4 covalent bonds
Melting + boiling points of giant covalent structures
High melting + boiling points - large amounts of energy are needed to overcome their strong covalent bonds
Electrical conductivity of giant covalent structures
- Most substances have no charged particles that are free to move, so most cannot conduct electricity
- Graphite is an exception
Metallic bonding
- Metals form giant structures in which electrons in the outer shells of atoms can move
- The metallic bond is the strong electrostatic forces of attraction between metal ions (+) and delocalised electrons (-)
Metallic elements/ions
- Na+, sodium
- K+ potassium
- Li+, lithium
- Ca2+, calcium
- Cu2+, copper (II)
Melting + boiling points of metals
- High melting + boiling points (strong metallic bonds)
- Energy is needed to overcome the forces of attraction between the metal ions and delocalised electrons
- Metals form lattices, so there is a large number of electrostatic forces to be broken
Electrical conductivity of metals
- Delocalised electrons can travel through the lattice structure, so an electric current can be formed. Therefore, metals can conduct electricity
- Metals IONS and NOT able to move (held in fixed positions)
Why graphite is slippery
The forces between the layers in graphite are weak. This means that the layers can slide over each other.
Giant ionic lattices
- No limit to the number of particles present
- Regular arrangement of ions
- Each ion is surrounded by ions with opposite charges
- high melting + boiling points because it takes a lot of energy to overcome strong electrostatic forces of attraction between oppositely charged ions
Physical properties of metals
- High melting/boiling points - lots of electrostatic forces to be broken
- Good conductors of heat and electricity - delocalised electrons
- High density - atoms packed closely into a small space
- Malleable + ductile - atoms can roll over each other into new positions without breaking the metallic bond
Why relative molecular mass causes melting + boiling points to increase
This is because larger molecules have more intermolecular forces between them. These forces, although weak, must be overcome if the substance is to boil.
