Topic 2 Structure and bonding - Ionic bonding(School curriculum) Topic 1 in CPG and PMT Flashcards
Ions, ionic bonding, properties of ionic compounds
What is an ionic bond?
A bond between a metal and non-metal involving the transfer of electrons.
In terms of electrons, describe what happens to the metal and non-metal when an ionic bond forms
The metal atom loses electrons to become a positively charged ion (cation)
The non metal gains electrons to become a negatively charge ion (anion).
What is an ion?
An ion is an atom or group of atoms with a positive or negative charge.
If an ion is positively charged, has it lost or gained electrons?
It has lost electrons. There are fewer negatively charged electrons to cancel out the charge of the positive protons. This means the overall charge becomes positive.
Na+ (+ should be up high) has the atomic number 11 and the mass number 23. How many protons, neutrons and electrons are in this ion?
Protons: 11
Electrons: 10
Neutrons: 12
O2- (2- should be up high and smaller) has the atomic number 8 and the mass number is 16. How many protons, neutrons and electrons are in this ion?
Protons: 8
Electrons: 10
Neutrons: 8
Why do elements in groups 1, 2, 6 and 7 readily form ions?
So they become more stable and achieve the electron structure of the noble gases (group 8).
What type of ions do elements in group 1 and 2 form?
Cations (positive)
- Group 1 metals will form 1+ ions
- Group 2 metals will form 2+ ions
What type of ions do elements in groups 6 and 7 form?
They are non-metals so form anions (negative)
- Group 6 will form 2- ions
- Group 7 will form 1- ions
What does it mean if an ionic compound ends in -ide?
The compound contains 2 elements
What does it mean if an ionic compound ends in -ate?
The compound contains at least 3 elements, one of which is oxygen.
Describe the structure of an ionic compound
Lattice structure.
Regular arrangement of ions.
Ions held together by strong electrostatic forces between ions with opposite charges.
What is the chemical formula of sodium oxide, formed from Na+ and O 2- (2- should be up high and small)?
Na2(small and lower)O -Na2O
Charges must balance so 2 sodium ions are required.
What is the chemical formula of magnesium hydroxide, formed from Mg2+ and OH (2+ should be small and up higher)
Mg(OH)2 (small lower 2)
Charges must balance so 2 hydroxide ions are required.
What is a covalent bond?
A bond formed when an electron pair is shared between 2 atoms.
What forms as a result of covalent bonding?
A molecule
Draw a dot and cross diagram for the formation of methane (CH4) (little 4 at bottom)
See PMT flashcard 101
True or false?
‘Covalent bonds are weak’
FALSE
Covalent bonds are strong
Which is smaller, an atom or a molecule?
An atom.
Simple molecules consist of atoms joined by strong covalent bonds within the molecule.
Why do ionic compounds have high melting points?
Strong electrostatic attraction between the positive and negative ions requires a lot of energy to overcome.
When do ionic compounds conduct electricity?
Why?
When molten or aqueous (dissolved in water) because the ions are charged and free to move. When solid, the ions are fixed in an ionic lattice so can’t move.
Why do simple molecular compounds have low melting and boiling points?
They have weak intermolecular forces (forces between molecules) which only require a little energy to overcome.
Do simple molecular compounds conduct electricity? Why/why not?
No because there are no charged particles.
Do giant covalent structures have a high melting point? Explain your answer.
Yes because they have lots of strong covalent bonds which require a lot of energy to break.
How do metals conduct electricity and heat?
The positive ions are fixed in a sea of delocalised electrons. These electrons are free to move and carry charge/energy.
True or false?
‘Metals are insoluble in water’
True
Name two giant covalent structures formed from carbon atoms
Graphite
Diamond
Describe the structure of graphite
Each carbon atom bonded to 3 other carbon atoms.
Layers of hexagonal rings of carbon atoms.
Weak intermolecular forces between layers.
One delocalised electron per carbon atom.
Describe and explain the properties of graphite
Graphite is soft/slippery because there are only weak intermolecular forces between layers which allow the layers to slide over one another.
Graphite conducts electricity because there is one delocalised electron per carbon atom. The delocalised electrons are mobile charges.
Describe the structure of diamond
All carbon atoms are covalently bonded to four other carbon atoms.
No delocalised electrons.
Describe the properties of diamond
Very hard
Very high melting point
Doesn’t conduct electricity as there are no charged particles.
What are the uses of graphite? Why?
Electrodes because graphite conducts electricity and has a high melting point.
Lubricant because it’s slippery (the layers in graphite can slide over each other).
Why is diamond used in cutting tools?
It’s very hard.
What is fullerene?
Fullerene is a molecule made of carbon, shaped like a closed tube or hollow ball.
Name two fullerenes
Graphene
C60 (should be lower little 60) (buckminsterfullerene)
What are properties of fullerene C60 (should be lower little 60)?
- Slippery due to weak intermolecular forces.
- Low melting point.
- Spherical.
- Strong covalent bonds between carbon atoms in a molecule.
- Large surface area.
What are the properties of graphene?
- High melting point due to covalent bonding between carbon atoms.
- Conducts electricity because it has delocalised electrons.
Why is graphene useful in electronics?
It is extremely strong and has delocalised electrons which are free to move and carry charge.
It is only one atom thick as it is a single layer of graphite.
What is a polymer? Name a polymer
Long chain molecules formed from many monomers.
E.g. poly(ethene)
Draw the structure of poly(ethene)
See p43 CPG
What bond is formed between carbon atoms in polymer molecules?
Covalent bonds
What are the properties of metals?
- High melting point.
- High density.
- Good conductors of electricity.
- Malleable and ductile.
- Generally shiny.
Explain why metals are malleable
The atoms are arranged in uniform rows which can slide over one another.
Explain why metals can conduct electricity
The electrons in the metal are charges that can move.
What are the properties of non-metals?
- Low boiling points.
- Poor conductors of electricity.
- Brittle when solid.
List the limitations of the following models when representing ionic compounds:
dot and cross
2D diagrams and
3D diagrams
- Dot and cross - no lattice structure or ionic bonds
- 2D diagrams - only shows one layer, doesn’t show formation of ions.
- 3D diagrams - shows spaces between the ions, doesn’t show charges.
List the limitations of the following models when representing covalent molecules:
Dot and cross and
Ball and stick
Dot and cross - doesn’t show relative sizes of atoms or intermolecular forces.
Ball and stick - bonds shown as sticks rather than forces, doesn’t show how covalent bonds form.
