2. Bonding and structure ( IONIC)
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What is ionic bonding
The strong electrostatic attraction between 2 oppositely charged ions
What must you draw when drawing ionic compounds
Brackets around compound with the charge
What structure do ionic compounds form
Giant ionic lattices
What is ionic bonding formed from
The transfer of electrons between metals and non metals in order to gain a full outer shell
Give 4 properties of ionic compounds
High melting and boiling points Brittle and easily cleaved Soluble in water Conduct electricity when molten or aqueous
Explain why ionic compounds are brittle
They are brittle because when the ions are forced out of position, like charges line up and cause repulsion and cracking of the ionic compound.
Explain why an Na ion has a 1+ charge
The atom has lost an electron so there is now 10 electrons but still 11 protons so an overall 1+ charge
How do ions size change compared to their atoms
• positive ions (cations) get smaller • negative ions (anions) get bigger
Give 2 main properties that affect the strength of electrostatic attraction in ionic compounds so therefore the melting point
Size of the charge - greater charge = stronger electrostatic force of attraction (more energy required to overcome..) Ionic radius (size of ion) - smaller sized ions packed more closely = stronger electrostatic attraction –> smaller sized ion + greater charge = high charge density
Trends in ionic radii for isoelectric ions
Ionic radii decreases • same number of electrons yet differing proton numbers • as proton number increases the ionic radius decreases as there is a greater nuclear charge on the same amount of electrons
Trends in ionic radii (down the group)
The ionic radius increases down a group as there are more electron shells
Give an experiment to show the evidence for charged particles
Electrolysis of copper (II) chromate (IV) chopper chromate solution = green when a current is passed through solution: BLUE Cu 2+ ions = attracted to negative cathode YELLOW CrO4 2- ions = attracted to positive anode
What is water of crystallisation
When a compound contains water molecules bonded into the crystal structure
How is water of crystallisation shown in a compound
Shown using a dot Eg - CaSO4.2H20 –> note, the number after the dot affects the total Mr of the compound - the Mr of water (18) should be timsed by that number (18x2 in this case)
What is a hydrated compound
A compound that contains water of crystallisation
What does an anhydrous compound mean
It does not contain water of crystallisation as it has been heated so the bonds have been broken and the water has been removed as steam
Describe how you would work out the value of water of crystallisation from the mass of the hydrated compound and anhydrous compound —> MGSO4.xH20
—> use the same method as empirical formula 1) subtract the mass of hydrated compound away from anhydrous compound to work out mass of water (first one subtract second ) 2) work out the number of moles of anhydrous compound and moles of water 3) divide both moles by the smallest number of moles to get a ratio
How do ionic substances dissolve
The ions become hydrated - the - and + ions are surrounded by water molecules. There is a strong attraction between the delta positive H in water and the negative ion. There is a strong attraction between the delta negative O in water and positive ion When a solid ionic lattice dissolved in water, the bonds between the ions break to give free ions which is endothermic and the bonds between the ions and the water are made which is exothermic Do NOT talk about intermolecular forces