SC5 Ionic Bonding
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Define ‘bonds’
Forces of attraction that hold atoms together
Define ion
An atom or a group of atoms with a positive or negative charge
How do ions form?
When atoms gain or lose electrons in their outermost shell
What kind of ions do metals form?
Cations: positively charged, because they tend to lose electrons
What kind of ions do non-metals form?
Anions: negatively charged, because they tend to gain electrons
Explain the what dot and cross diagrams are
• models the transfer of electrons between two atoms • one atom will have electrons represented by dots • and the other will have electrons represented by a cross • the non-metal will gain electrons, which will be different to the shapes used to represent its own electrons
Describe the limitations in dot and cross diagrams.
Doesn’t show the three-dimensional shape of the molecule.
Why do ionic bonds occur?
So that atoms can gain a full outer shell
What is an ionic lattice?
The regular arrangement of ions in an ionic substance
How do we work out the number of electrons in an ionic substance?
• Work out how many electrons a neutral atom would have (same as the proton number) • Work out how many electrons have been lost or gained • -ve means electrons have been gained • +ve means electrons have been lost • Calculate the number of ions in an atom plus electrons gained or minus electrons lost
How will elements in group 1 form ions?
They will lose the electron in their outermost shell and form 1+ ions
How will elements in group 2 form ions?
They will lose the two electrons in their outermost shell and form 2+ ions
How will elements in group 6 form ions?
They will gain two electrons in their outermost shell and form 2- ions
Why is the ionic lattice formed in ionic substances?
Ions attract each other and form a regular pattern with oppositely charged ions next to each other
What are ionic bonds?
Strong electrostatic forces between oppositely charged ions, which spread in all directions within an ionic lattice
Describe some properties of ionic compounds
• high melting and boiling points • can conduct electricity when molten
What are the two conditions that a substance has to meet for it to be able to conduct electricity?
• must contain charged particles • particles must be able to move freely
Why do ionic substances have high melting and boiling points?
• electrostatic forces of attraction between oppositely charged ions are strong • a lot of energy is required to overtake these bonds in order to separate and melt the lattice structure • therefore requiring high temperatures
Why can ionic substances only conduct electricity when molten?
The ions are free to move and carry charge
When are the endings -ate and -ide used?
Used for the negatively charged ions in the compound
What does the ending -ate mean a compound contains?
3 elements, one of which is oxygen
What does the ending -ide mean a compound contains?
2 elements, one of which is a non-metal
Name some examples of compounds ending in -ide
• sodium chloride • magnesium oxide • calcium sulphide • potassium iodide • ions sulfide
Name some examples of compounds ending in -ate
• magnesium carbonate • sodium nitrate • copper sulphate • potassium iodate • iron sulphate