Flashcards in C4b Deck (11):
What is an ion?
A charged atom or group of atoms.
How do you recognise an ion, atom and a molecule from given formulae?
An ion will have a little plus or minus sign on it.
An atom is a single element.
A molecule is a group of atoms.
What atoms have a stable electronic structure?
Atoms with an outer shell of 8 (a full outer shell).
How and why do metal atoms form positive ions and non metal atoms form negative ions?
When metals form ions, they lose electrons to form positive ions. When non-metals form ions, they gain electrons to form negative ions. So when a metal and a non-metal combine, they form ionic bonds by transferring electrons to form positive ions and negative ions which then attract one another.
How do you deduce the formula of an ionic compound from the formula of the positive and negative ions?
You have to balance the positive and negative charges.
For example, potassium chloride K+ + Cl- = KCl
The potassium ion is 1+ and the chloride ion is 1-, so they balance.
What do 'dot and cross' diagrams show?
What happens to the electrons in ionic bonds. All atoms end up with full outer shells as a result of this giving and taking of electrons. LEARN HOW TO DRAW.
What is the electrical conductivity of sodium chloride in solid, molten liquid and solution like?
Ionic compounds do not conduct electricity when they are solid.
When NaCl melt, the ions are free to move and they'll conduct electricity.
NaCl dissolves to form a solution that conducts electricity. When dissolved the ions separate and are all free to move in the solution, so they can carry electrical current.
How do the melting points of sodium chloride and magnesium oxide compare?
They both have high melting and boiling points. This is due to the very strong attraction between oppositely charged ions in the giant structures. To break the bonds you have to overcome these attractive forces - this takes a lot of energy. MgO has a higher melting point than NaCl. Its ions have double the charge of sodium chloride ions, so the attraction between them is harder to overcome. O2- ions are also smaller than CL- ions, so the ions in MgO can pack together more closely, making the attraction between them harder to overcome.
Does magnesium conduct electricity when molten?
Yes, the ions are free to move and they'll conduct electricity.
What is the structure of sodium chloride and magnesium oxide?
Giant ionic lattices in which positive ions are strongly attracted to negative ions.