Topic 2- Bonding, Structure and Properties of matter Flashcards
What is ionic bonding?
Actual meaning
Ionic bonding is the electrostatic attraction between positive and negative ions. (non- metals + metals)
Describe ionic bonding:
When group 1 or 2 elements (metals) lose electrons, to form positive ions (cations), to group 6 or 7 elements (non-metals) to form negative ions. (anions)
How are ionic bonds held together?
They are held together in a giant lattice. The electrostatic attraction between the positive and negative ions hold the structure together
State properties of ionic substances
Molten
- High melting and boiling points.
- Does not conduct electricity when solid.
- Conducts electricity when molten or dissolved in water (electrons free to move).
How are ionic compounds formed? Use MgO example.
The metal transfers its outer electron to the non-metal.
Magnesium has two outer electrons to transfer to oxygen who can only accept 2 electrons to get a full outer shell.
Are ionic bonds strong? Explain how.
Ions with opposite charges attract each other to create ionic bonds.
What are covalent bonds?
When two atoms share a pair of electrons.
Describe the structure and properties of simple molecular covalent substances (water, hydrogen) :
- They do not conduct electricity
- Small molecules
- Weak intermolecular forces between molecules therefore:
- low melting and boiling points
How do intermolecular forces change as the mass/size of the molecule increase?
They increase which causes melting/boiling points to increase as well (more energy needed to overcome these forces).
What are polymers?
Polymers are very large molecules with atoms linked by covalent bonds. there are no bonds between polymer chains, strong intermolecular forces ensure that the structure is solid at room temperature.
What are giant covalent structures?
- atoms covalently bonded together in a giant lattice.
- high melting and bps
- mostly don’t conduct electricity (no delocalised electrons)
- diamond, graphite, silicon dioxide
What is metallic bonding?
The force of attraction between delocalised electrons and positive metal ions.
Describe properties of metals:
-High melting and boiling points
-malleable, soft
-layers of atoms can slide over each other
good conductors of heat and electricity
What are alloys?
- Mixture of metals with other elements.
- Different sizes of atoms distort the layers, therefore they cannot slide over each other and are harder than pure metals.
What are the disadvantages of a dot and cross diagram and a ball and stick diagram?
Dot and cross: It does not show how the ions are arranged in space. A dot and cross diagram for sodium chloride suggests that it is made up of pairs of sodium and chloride ions. It is not.
Ball and stick: Fails at indicating the movement of electrons. The atoms are placed far apart from each other, which in reality is not the case as the gaps between atoms are much smaller.
