AQA unit 2

the nucleus
1) in the middle of atom
2) contains protons and neutrons
3) positive charge because of protons
4) almost whole mass of atom in nucleus
5) small size compared to rest of atom
the eletron
1) move around the nucleus
2) negatively charged
3) tiny but cover a lot of space
4) radius determines size of atom
5) virtually no mass
6) occupy shell around nucleus
relative mass and charge
partcle mass charge
proton 1 +1
neutron 1 0
electron very small -1
atomic and mass number
the mass number = number of protons and neutrons
atomic number = number of protons or electrons
elements and compounds
elements are one type of atom e.g oxygen
compounds are chemically bonded e.g water
different atomic forms of the same element which have same number of protons/electons, but a different number of neutrons and therefore a different mass number e.g carbon 14 (c-14) used for carbon dating
periodic table order
modern table shows elements in order of ascending atomic number
elements with similar properties are grouped in the same column
these groups correspond to the amount of electrons in the outer shell e.g group 1 elements = alkali metals
group 7 elements = halogens
group 0/8 elements = noble gases
electron configuration
electron shells
shell 1 always has 2 electrons (unless it’s hydrogen which has 1)
shell 2 up to 8 electons
shell 3 up to 8 electrons
shell 4 up to 8 electrons etc
atoms are much happier with full electron shells like the noble gases.
in most atoms the shell is not full and this makes the atom want to react by losing or gaining electons
ionic bonding
lose or gain electrons to form charged particles called ions because they are charged they are then attracted to the opposite charge
elements on lhs have low no of electrons in outer shell and want to get rid of the excess electrons whilst those on the right with almost full outer shells want to gain electrons
ionic structures
ionic bonds always produce giant ionic structures
they form a closely packed regular lattice arrangement.
strong chemical bonds between ions
don’t melt easily as have high melting and boiling points because of strong chemical bonds.
dissolve to form solutions which conduct electricity because ions separate and are free to move.
conduct electricity when molten also
covalent bonding
sometimes atoms prefere to share electrons rather than give or take. this way both atoms gain full outer shell so are happy!
each covalent bond provides one extra shared electron for each atom
eg hydrogen always shares with other hydrogens to make H2
eg Cl2, HCl, NH3 (ammonia),CH4(methane), H2O, O2
covalent substances
either simple molecules or giant structures
simple molecular substances have very strong covalent bonds to form small molecules, low melting and boiling points therefore most are gases or liquids, don’t conduct electricity as no ions.
Giant covalent structures are similar to ionic structures but without ions so no charge. all bonded by strong covalent bonds. very high melting and boiling points, do not conduct electricity.
insoluable eg diamond and graphite made from carbon
isotope of carbon. Each carbon atom has 4 covelant bonds in a very rigid covelant structure. hardest natural substance which makes it useful fo drill tips.
metallic structures
metallic bonds involve free electrons in the outer shell. which produce all the properties of metals. electrons are free to move so metals are good conductors of heat and electricity.
the electrons hold together in regular structeres. also allow atoms to slide over each other causing metals to be malleable.
types of substance
ionic; giant covelant; simple molecular or metalic
nano particles
nano particles are particles which are 1nm (0.000000001mm) long these include fullerenes which are molecules of carbon shaped as hollow balls or closed tubes
smallest is buckminster fullerene which is 60 carbon atoms joined in a ball
properties of nano particles
huge surface area, good industrial catalysts, can be used to make sensors e.g. sensors to test water purity
relative atomic mass
same as the mass number which the top number in the periodic table. It is relative as it is compared to the mass number of carbon 12.

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