chemistry topic 2 (copy)

what are ions?

charged particles

why do atoms become ions?

to become stable/ full outer shell

how do metals form ions?

lose electrons to become positive

how do non-metals form ions?

gain electrons to become negative

what atoms react together and why?

non-metal and metal because they have opposite charges, to become stable

what happens when atoms react (ionic bonding)?

they become strongly attracted to eachother by electrostatic forces (called ionic bonding)

what do dot and cross diagrams show?

the arrangement of electrons in an atom or ion. each electron is represented by a dot or cross

when do you use dot and cross diagrams?

for ionic bonding (non metal + metal)

what are disadvantages of dot and cross diagrams? (3)

doesn’t show the structure of the compound, the size of ions, or how they’re arranged

what are ionic compounds?

compounds that only contain ionic bonds

what is ionic bonding?

the strong electrostatic forces of attraction between oppositely charged metal and non-metal ions

what force is in ionic bonding?

(very strong) electrostatic forces of attraction

what structure are ionic compounds?

giant ionic lattice

what is a giant ionic lattice?

large number of ions regularly arranged in a repeating pattern, repeated in all directions making a giant 3D lattice structure

what is table salt as an element?

sodium chloride

describe advantages of a ball and stick model (3)

shows the regular pattern of an ionic crystal, how the ions are arranged and suggests that the crystal extends beyond whats shown in the diagram

describe disadvantages of a ball and stick model (2)

isn’t to scale so relative sizes of the ions may not be shown, and in reality there aren’t gaps between ions

describe advantages of model 2 of ionic compounds (2)

shows relative sizes of the ions and the regular pattern of an ionic crystal

describe a disadvantage of model 2 of ionic compounds (1)

only lets you see the outer layer of the compound

what are the melting and boiling points of ionic compounds like?

in giant ionic lattices, they’re high because it requires large amounts of energy to overcome the many strong electrostatic forces of attraction

can ionic compounds conduct electricity?

they can only conduct when molten (liquid) or dissolved in a solution, as ions (charged particles) are present, free to move and carry a charge throughout the circuit

what happens when non metal atoms bond together?

they share pairs of electrons to make covalent bonds

what is a covalent bond?

when atoms share electrons with each other so they both have full outer shells (to become stable)

how is the positive nuclei (of the bonded atoms) attracted to the shared pair of electrons?

by electrostatic forces, making covalent bonds very strong

why do atoms only share electrons in their outer shells?

they have the highest energy levels

where does covalent bonding happen?

in 2 non metals

what diagram do you use to show covalent bonds?

dot and cross diagrams

why are dot and cross diagrams useful for covalent bonds? (1)

they show which atoms the electrons in a covalent bond come from

why are dot and cross diagrams not useful for covalent bonds? (2)

doesn’t show relative sizes of atoms, or how they are arranged in the space

what are advantages of stick diagrams? (1)

show how atoms are connected in large molecules

what are disadvantages of stick models? (2)

don’t show 3D structure of molecules, or which atoms the electrons in the covalent bond have come from

what are advantages of 3d models? (2)

shows the atoms and the covalent bonds, and their arrangement in the space next to each other

what are disadvantages of 3d models? (2)

they can be confusing because there are lots of atoms to include, and doesn’t show where the electrons in the bonds have come from

what are simple molecular substances?

made up of molecules containing a few atoms joined together by covalent bonds

what do substances containing covalent bonds usually have?

simple molecular substances

what are the atoms between the molecules (in covalent bonds) held together by?

very strong covalent bonds

in covalent bonds, how weak/ strong are the the forces of attraction between the molecules

VERY weak

why do covalent bonds have low melting/boiling points?

they’re simple molecules, so the weak forces of attraction between covalent molecules in a liquid phase (intermolecular forces) can be overcome with little heat energy

what state of matter are most molecular substances at room temp?

gases or liquids

what happens as molecules get bigger (in simple molecular bonds)

the strength of intermolecular forces increases, so more energy is required to break them, so melting and boiling points increase

do molecular compounds conduct electricity?

no, because they aren’t charged, so there are no free electrons or ions

how are giant covalent structures bonded together?

strong covalent bonds

are the melting and boiling points high in giant covalent structures and why?

yes, very high, as lots of energy is required to break the covalent bonds between the atoms

why don’t the atoms in giant covalent structures conduct electricity?

dont contain charged particles

describe the physical appearance of diamonds

each carbon atom forms 4 covalent bonds in a very rigid giant covalent structure

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describe the physical appearance of graphite

each carbon atom forms 3 covalent bonds, to create layers of hexagons. each carbon atom also has 1 delocalised electron

describe the physical appearance of silicon dioxide

this is what sand is made of. each grain of sand is 1 giant structure of silicon and oxygen

what is an allotrope?

different structural forms of the same element in the same physical appearance

why are diamonds really hard? ;)

because it has a giant covalent structure, made up of carbon atoms that each form 4 covalent bonds. (Rigid tetrahedral shape)

why does diamonds have very high melting/ boiling points?

there are many strong covalent bonds between every carbon atom

does diamond conduct electricity?

no, there are no charged particles (no free electrons)

why is graphite an ideal lubricating material?

there aren’t many covalent bonds between layers, they’re held together weakly. This means they’re free to move over each other, so it is soft and slippery

is graphite’s melting point high or low, and why?

high, because the covalent bonds in the layers need loads of energy to break them

how many of carbons outer electrons are used in bonds?

3

how does the amount of outer electrons affect graphites properties?

it means each carbon atom has 1 delocalised electron, and can move, so graphite conducts electricity and thermal energy

what is graphene?

a sheet of carbon atoms joined together in hexagons

how thick is the sheet of carbon atoms in graphene?

one atom thick, making it 2D

is graphene strong or not?

it’s very strong, as there is a network of covalent bonds

why is graphene used to make composite materials stronger?

it’s incredibly light, so will improve their strength without adding much weight

can graphene conduct electricity and why?

yes, it has delocalised electrons so it can conduct electricity through the whole structure

what substances contain the same atoms (carbon)?

diamond, graphite, graphene

what are fullerenes?

molecules of carbon, shaped like closed tubes or hollow balls

what was the first fullerene to be discovered?

Buckminsterfullerene

what is the molecular formula of Buckminsterfullerene?

C(60)

what does the carbon atoms in buckminsterfullerene form?

a hollow sphere containing 20 hexagons and 12 pentagons

what can fullerenes be used to do?

to cage other molecules

what does the fullerene structure form around?

another atom or molecule, which is trapped inside the fullerene. This can be used for delivering drugs around the body

what can fullerenes be used for? (4)

delivering drugs around the body, catalysts, (spherical fullerenes for) lubricants, (cylindrical fullerenes for) strengthening materials

what is a benefit of fullerenes large surface areas'?

they can help make great industrial catalysts. Individual catalyst molecules could be attached to the fullerenes

what can fullerenes form?

nanotubes

what are nanotubes?

tiny carbon cylinders

what is the ratio between the length and the diameter of nanotubes?

very high

why can nanotubes conduct electricity and thermal energy?

delocalised electrons can move throughout the structure

why do nanotubes have a high tensile strength (strong)?

because of high length to diameter ratio, many strong covalent bonds

why do nanotubes have a high melting point?

because each atom is covalently bonded to 3 others

what is the technology that uses very small particles like nanotubes?

nanotechnology

what can nanotubes be used in?

in electronics, or to strengthen materials without adding much weight

what are most polymers held together by?

covalent bonds

what happens in a polymer?

lots of small units are linked together to form a long molecule that has repeating sections.

what is the short section you can draw out for a polymer instead of the whole molecule?

the repeating unit

what is this polymer called?

poly(ethene)

what is the bit in the brackets?

the repeating unit

what does the bonds through the bracket join up to?

the next repeating unit

what is the n in the polymer?

the symbol that tells you the unit is repeated lots of times

how do you find the molecular formula of a polymer? (make an example for poly(ethene))

write down the molecular formula of the repeating unit in brackets, and put an ‘n’ outside. eg. poly(ethene) = (C2H4)n

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are the intermolecular forces between polymer molecules smaller or larger than simple covalent molecules?

larger than between simple covalent molecules, so more energy is needed to break them

what state are most polymers?

solid (s)

are the intermolecular forces between polymer molecules smaller or larger than ionic or covalent bonds?

smaller and weaker, so they generally have lower boiling points than ionic or giant molecular compounds

what do metals consist of?

a giant structure

what electrons in metals are delocalised?

the electrons in the outer shell

what force is between the positive metal ions and the shared negative electrons?

strong electrostatic forces of attraction

what do the forces of attraction in metals do?

they hold the atoms together in a regular structure and are known as metallic bonding

is metallic bonding strong or weak?

strong

what does the substances held together by metallic bonding include?

metallic elements and alloys

what produces all the properties of metals in metallic bonds?

delocalised electrons

is the electrostatic forces between the metal atoms and the delocalised sea of electrons strong or weak?

strong, so they need lots of energy to be broken

what does the strong electrostatic forces in a metal mean?

most compounds with metallic bonds have very high melting and boiling points, so they are generally solid at room temperature

why are metals good conductors of heat and electricity?

they carry electrical charge and thermal energy through the whole structure, so they are good conductors of electricity and heat

what can the layers of atoms in a metal do?

they can slide over each other, making metals malleable, which means that they can be bent, hammered or rolled into flat sheets

why arent pure metals good for certain metallic bonding jobs?

because they are often too soft when they are pure, so they’re mixed with other elements to make them harder ;)