Chemical bonds (2.1) (M) Flashcards
What are the three types of bonds?
- covalent
- ionic
- metallic
For ionic bonding the particles are…
oppositely charged ions
For covalent bonding the particles are…
atoms which share pairs of electrons
For metallic bonding the particles are…
atoms which share delocalised electrons
Where does ionic bonding occur?
in compounds formed from metals combined with non-metals
Where does covalent bonding occur?
in most non-metallic elements and in compounds of non-metals
Where does metallic bonding occur?
in metallic elements and alloys
i.e. Ionic bonding
What happens when a metal atom reacts with a non-metal atom?
The electrons in the outer shell of the metal atom are transferred.
Metal atoms lose electrons to become positively charged ions.
Non-metal atoms gain electrons to become negatively charged ions
The ions produced by Group 1, 2, 6 and 7 elements have the electronic structure of what?
a noble gas (Group 0)
How can the electron transfer during the formation of an ionic compound be represented?
by a dot and cross diagram
note, in this diagram, you can draw a circle (resembling a shell) around the symbol
What would be the ionic charge on a group 2 and group 7 ion?
Group 2: 2+
Group 7: -
How is an ionic compound described?
a giant structure of ions (i.e. a giant ionic lattice)
2 points
What are ionic compounds held together by?
strong electrostatic forces of attraction between oppositely charged ions
these forces act in all directions in the lattice
2 ways
How can the structure of an ionic compound/lattice be represented in a 3D form?
Ball and stick model, 3D space filling model
What is a common example of a giant (ionic) lattice?
Sodium chloride
What is the relation in number of ions in NaCl?
The number of Na ions and Cl ions are equal
What is the limitation of the dot-and-cross model to show giant ionic lattices?
only 2D
Does not show the shape
Does not show how ions are arranged in space (e.g. suggests NaCl is made up of pairs of sodium and chlorine ions, it is not)
What is the limitation of the ball and stick model to show giant ionic lattices?
- suggests there are gaps between ions when there is not
- suggests atoms are solid inelastic spheres - they are mostly made up of of empty space
- using sticks for bonds is misleading because the forces of attraction between ions actually act in all directions
- relative size of ions compared to each other is not to scale
What is the limitation of the 2D space-filling model to show giant ionic lattices?
shows the arrangement in one layer only, not the next
What is the limitation of the 3D space-filling model to show giant ionic lattices?
- ions are not solid spheres
- difficult to see 3D arrangement clearly
What are covalent bonds?
when atoms share pairs of electrons
What are the bonds between atoms in covalent bonds like? (within the molecules themselves)
They are strong
What are the two types of covalently bonded substances?
small (simple) molecules or giant covalent structures
What is a common example of a covalently bonded substance that has very large molecules?
Polymers
3 needed
What are examples of covalently bonded substances that have giant covalent structures?
diamond, graphite (allotropes of carbon) and silicon dioxide (silica)
4 ways
How can covalent bonds in molecules and giant structures can be represented? (excluding polymers)
note where shared electrons are situated in teh dot and cross diagram
How can polymers be represented?
4 points
Describe the structure of metals
- giant structures of atoms arranged in a regular pattern
- layers of atoms
- lattice of positive ions
- with a sea of delocalised electrons
- (strong) electrostatic forces of attraction between positive ions and electrons
How would you describe the electrons in the outer shell of metal atoms? What does this allow?
delocalised
and so are free to move through the whole structure
What does the sharing of delocalised electrons in metallic bonds cause?
strong metallic bonds
2 forms
What are the forms that metallic bonds may be represented in?
How do covalent bonds hold two atoms together?
electrostatic force of attraction between shared pair of negatively charged electrons and both positively charged nuclei
Why can metals be bent and shaped?
They consist of layers, which slide over eachother
Why should a reaction where halogen gases are given out be doe in a fume cupboard?
Halogen gases are toxic
2 needed
What is a limitation of the dot and cross diagram to represent a simple molecule?
does not show shape of molecule
only 2D
Why does ammonia have a low melting point?
Ammonia is a simple molecule/has small molecules
with weak intermolecular forces
it take little energy to overcome these intermolecular forces
2 marks
Why may corrosion reduce the electrical conductivity of a metal?
Metal oxide formed
ions are not free to move or electrons cannot move through the structure
I assume this is the same for alloys
What happens when two atoms of potassium react with one atom of sulfur? (give answer in terms of electron transfer and state ions formed)
electrons transferred from potassium to sulfur
two potassium atoms each lose one electron
forming K+ ions
sulfur atoms gain 2 electrons
forming S2- ions
What are the 2 limitations of the simple model?
It is only 2D
Particles shown as solid
