bonding, structure and properties of matter Flashcards
What is a cation?
A positively charged ion that has lost electrons
What is an anion?
A negatively charged ion that has gained electrons
What force holds together an ionic bond?
Electrostatic forces
Describe the process of ionic bonding between sodium and chlorine?
Sodium is a group 1 element and chlorine is a group 7 element so in order to become stable, sodium gives an electron to chlorine, giving it a charge of +1 and chlorine gains an electron, giving it a charge of -1.
How do you draw a dot and cross diagram?
Draw only the valence shell of each ion and draw on the crosses and dots to represent electrons. Draw brackets around the circle with the charge in the top right hand corner.
What are some properties of ionic compounds?
high melting and boiling points, not conductors when solid, conductors when liquid due to free moving ions, some separate in water
Why do ionic compounds have high melting and boiling points?
Strong electrostatic forces between the ions require lots of thermal energy to overcome.
Why do some ionic compounds only conduct electricity when dissolved in water?
The ions separate and are free to move so they can carry electric current
What is a triple covalent bond?
An atom that needs three atoms to complete its outer shell such as nitrogen shares 3 electrons with another atom.
What is a double covalent bond?
Atoms such as oxygen that need two electrons to fill its valence shell share two electrons
Describe the forces and bonds in simple molecular structures
The electrostatic forces bonding the atoms within the molecules are strong whereas the intermolecular forces between the molecules that make up a substance are weak
Why do substances with simple covalent molecules have low boiling and melting points?
To melt or boil a simple molecular compound, you only have to overcome the weak intermolecular forces, requiring little energy. The strong covalent bond does not have to be broken.
Why do melting and boiling points increase as covalent molecules increase in size?
The strength of the intermolecular force increases so more energy is required to break them
Why don’t molecular compounds conduct electricity?
They aren’t charged so there are no free electrons or ions
What are polymers?
Long chains of repeating units covalently bonded together
How is a polymer represented?
Draw a single repeating section of the polymer, with lines leading outwards to indicate continuation and draw brackets around it. On the bottom right hand corner, outside of the brackets, write the number of times the unit repeats in the polymer
Why are most polymers solid at room temperature?
Polymers have higher melting and boiling points due to stronger intermolecular forces to overcome.
What are some properties of giant covalent structures?
high melting and boiling points, do not contain charged particles and most do not conduct electricity
What is the structure of diamond?
Each carbon forms four covalent bonds
What is the structure of graphite?
Each carbon forms three covalent bonds to create layers of hexagons. Each atom has one delocalised electron
What is the structure of silica?
Each silicon is bonded to two oxygens
Which giant covalent structures conduct electricity?
Graphite and graphene
Why is graphite soft?
There are no covalent bonds between the layers so they are free to move over each other, making it a good lubricating material
What are fullerenes?
Carbon allotropes shaped like closed tubes or hollow balls
What is an allotrope?
A different form of the same element in the same state
What is the structure of Buckminsterfullerene?
hollow sphere shape containing 60 carbon atoms made up of 20 hexagons and 12 pentagons
What are some properties of nanotubes?
high ratio between length and diameter, conductors of electricity and heat, high tensile strength (doesn’t break when stretched), lightweight
What is metallic bonding?
The electrostatic attraction between positive metal ions and delocalised electrons
Why are metals conductors?
the electrons in the outer shell of metal atoms are delocalised so can carry charge and heat
Why are pure metals malleable and alloys hard?
Pure metals have layers of atoms that can slide over one another whereas alloys have a mixture of different metals of different sized atoms, making it more difficult for the layers of atoms to slide over each other
Describe solids in terms of particle arrangement, energy and movement
regular lattice arrangement, fixed positions, strong forces of attraction between particles, particles vibrate, have low energy, keep a definite shape
Describe liquids in terms of particle arrangement, energy and movement
randomly arranged but close together, weak force of attraction, do not keep a definite shape, constantly moving randomly, higher energy
Describe gases in terms of particle arrangement, energy and movement
random arrangement, free to move and far apart, very weak forces of attraction between particles, constantly moving rapidly with high energy
What are nanoparticles?
Particles that contain only a few hundred atoms with extremely small diameters
Why do nanoparticles make effective catalysts?
nanoparticles have a large surface area to volume ratio so you do not need as much as regular particles
What are some uses of nanoparticles?
blocking UV rays in sun cream, used in moisturisers, some conduct electricity
