chemistry 2 Flashcards
What is ionic bonding
Ionic bonding is the electrostatic attraction between positive ions and negative ions. It is relatively strong attraction
How are ionic compounds held together
a giant structure of ions, held together by strong electrostatic forces of attraction between oppositely charged ions.Held in a giant lattice.
State properties of ionic substances
High melting/boiling point
Don’t conduct electricity when solid
Conduct when molten or dissolved in water-ions are free to move
giant covalent structures
consist of many atoms covalently bonded in a lattice structure
What is important when working out a formula of an ionic compound
Ionic compounds are electrically neutral i.e, positive and negative charges cancel each other out
How are ionic compounds formed.Explain in terms of MgO
Reaction of a metal with a non-metal.Electron transfer occurs-metal gives away outer shell electrons to non-metal.
What is a covalent bond
A covalent bond is when two nonmetals share a pair of electrons.
Describe the structure and properties of simple molecular covalent substances
Don’t conduct electricity(no ions)
Small molecules
weak intermolecular forces
Low melting/boiling point
How do intermolecular forces change as size of molecules increase
They increase.That causes melting/boiling points to increase as well(more energy needed to overcome these forces
What are polymers
Polymers are very large molecules with atoms linked by covalent bonds
What are thermosoftening polymers
Special type of polymers.They melt/soften when heated.There are no bonds between polymer chains.Strong intermolecular forces ensure that the structure is solid at room temp.These forces are overcome with heating
What are giant covalent substances
-Solids,atoms covalently bonded together in a giant lattice
-High melting/boiling point-strong covalent bonds
-Mostly don’t conduct electricity
-Diamond,graphite,silicon oxide
diamond
in diamond each carbon is joined to 4 other carbons covalently.its very hard has high melting point and doesnt conduct electricity.
graphite
in graphite, each carbon is covalently bonded to 3 other carbons, form layers of hexagonal rings which have no covalent bonds between the layers.
How can layers in graphite slide over each other
the layers can slide over eachother due to no covalent bonds between the layers, but weak intermolecular forces meaning graphite is soft and slippery.
How are graphites similar to metals
one electron from each carbon atom is delocalised. this makes graphites similar to metals because of its delocalised electrons. it can conduct electricity unlike diamond
What is graphene
single layer of graphite,strong(atoms tightly bonded).
What are fullerenes
carbon can also form fullerenes with dif numbers of carbon atoms. molecules of carbon atoms with hollow shapes. they are based on a hexagonal rings of carbon atoms but may also have 5 or 7 carbon atoms.
what is buckminsterfullerene
first fullerene to be discovered which has a spherical shape
what are the uses of carbon nanotubes
they can be used as lubricants to deliver drugs in the bodies. nanotubes can be used for reinforcing materials, e.g tennis rackets
What are uses of nanoparticles
good catalysts high surface are to volume ratio, new cosmetics, lubricant coatings, nanotubes conduct electricity so can be used in circuits,
disadvantages of nanotubes
may be toxic to people, may be able to enter brain from blood stream and cause harm.
What is metallic bonding
Forces of attraction between delocalised electrons and nuclei of metal ions
Describe properties of metals
-High melting/boiling point(strong forces of attraction)
- Good conductors of heat and electricity(delocalised electrons)
-Malleable,soft(layers of atoms can slide over each other whilst maintaining the attraction forces
What are alloys?Why are they harder than pure metals?
Alloys: mixtures of metals with other elements, usually metals. Different sizes of atoms distorts the layers,so can’t slide over each other,therefore alloys are harder than pure metals
What are the limitations of the simple model
There are no forces between spheres and atoms,molecules and ions are solid spheres-this is not true
A pure substance will melt or boil at?
-A fixed temperature
-A mixture will melt over a range of temperatures
what is nanoscience
Science that studies particles that are 1-100 nm in size
State the uses of nanoparticles
-Medicine(drug delivery systems)
-Electronics
-Deodorants
-Sun creams(better skin coverage and more effective protection against cell damage
what does amount of energy need to change states from solid to liquid and liquid to gas depend on?
the strength of forces betwen the particles of the substance. the nature of the particles involved depends on the type of bonding and structure of the substance. the stronger the forces between the particles the higher melting/boiling point
what are limitations of the simple model
there are no forces between spheres and atoms, molecules and ions are solid spheres-this is false
give one use of a fullerene
catalyst
describe the limitations of using dot and cross, ball and stick, two and three-dimensional diagrams to represent a giant ionic structure
It does not, however, show the 3D lattice structure of an ionic compound or that this is a giant compound. Doesn’t show how ions are arranged in space
work out the empirical formula of an ionic compound from a given model or diagram that shows the ions in the structure.
The empirical formula of the compound can be worked out by the ratio of each ion present in the structure. In the diagram above there are equal numbers of sodium ions and chloride ions. This means the empirical formula is NaCl.
be familiar with the structure of sodium chloride
Ionic compounds such as sodium chloride are arranged in a giant three-dimensional lattice structure, which is a regular repeating pattern of positive and negative ions. There are strong electrostatic forces of attraction that hold the oppositely charged ions together in the giant lattice.
explain the different temperatures at which changes of state occur in terms of energy transfers and types of bonding
During a change of state, the energy of a substance is either absorbed or released as heat. For example, during melting, energy is absorbed as heat and during condensation, energy is released as heat.
explain the limitations of the particle theory in relation to changes of state when particles are represented by
solid inelastic spheres which have no forces between them.
there are no forces between the spheres, and that atoms, molecules and ions are not solid spheres.
how can ionic compounds still conduct electricity when melted or dissolved in water
When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and so charge can flow
how are intermolecular forces weak compared to with covalent bonds
with covalent bonds. lots of energy is needed to break them whereas with intermolecular forces. very little energy is needed to break them.
what is overcome when a substance melts or boils
intermolecular forces (weak forces between molecules) not covalent bonds
what is the effect on melting/boiling point with larger molecules
e intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points.
why are metals good conductors of thermal energy and and electricity
Metals are good conductors of electricity because the delocalised electrons in the metal carry electrical charge through the metal. Metals are good conductors of thermal energy because energy is transferred by the delocalised electrons.
why is graphite similar to metals
Graphite has delocalised electrons, just like metals. These electrons are free to move between the layers in graphite, so graphite can conduct electricity.
compare ‘nano’ dimensions to typical dimensions of atoms and molecules.
Nanoparticles are structures, 1-100 nanometres (nm) in size, that usually contain only a few hundred atoms . This means that nanoparticles are around 100 times larger than atoms and simple molecules
