CHEMISTRY- OCR B - SALTERS- ELEMENTS OF LIFE

HideShow resource information

Elements of Life:

amount of substance...

Avagadro's constant= 6.02x10^23

relative atomic mass (Ar) is the number of times heavier an atom is than one-twelfth of an atom of carbon 12. (no units)

relative formula mass (Mr) is the sum of the Ar's for each atom in a formula- can also be referred to as the relative molecular mass for simple molecular compounds (no units).

To obtain one mole of a substance, weigh out Ar or Mr exactly in grams.

The empirical formula is the simplest ratio of atoms in an element and the molecular formula is the actual number of atoms in an element.

Amount of moles= mass (g) / Mr or Ar

a simple model of the atom...

mass number= protons and neutrons - TOP number

atomic number= protons - BOTTOM number

number of electrons is equal to number of protons... number of neutrons is TOP number minus BOTTOM number.

Proton-mass=1-charge=1+

Neutron-mass=1-charge=0

electron-mass=negligible-charge=1-

Isotopes are atoms of the same element, they have different numbers of neutrons- a different mass number- but the same atomic number.

average Ar = (isotopic mass x abundance) + (isotopic mass x abundance)

100

nuclear reactions...

some isotopes have unstable nuclei- resulting in them being radioactive. 3 types of emission can be spontaneously produced, knocking electrons out of atoms forming ions- ionising radiation

ALPHA- helium nuclei - charge +2 - 2 less protons and neutrons - stopped by paper- low deflection by electric field

 BETA - electrons - charge -1 - 1 more proton, 1 less neutron - stopped by al foil - high deflection by electric field

GAMMA - EM radiation - no charge- no change to nucleus- lead stops it - no deflection by electric field.

examples:

alpha:

(http://alpcentauri.info/img29.gif)

beta:

(http://www.green-planet-solar-energy.com/images/beta-decay.gif)

Half-life, is the time taken for the radioactive nuclei to decay by half, this is a fixed value and isn't effected by temperature!

This process can be used to date any living thing (wood, bones...) ages of igneous rocks containing radioactive isotopes can also be estimated.

Tracers are radioactive isotopes whose decay is monitored. They are commonly used in the medicinal world to aid diagnosis. The tracer is monitored with a Geiger Muller tube/counter, its important the length of the half life is neither too long nor too short! Too long and it will remain in the body for too long- potentially causing harm. Too short and the source will be too small to trace!

Nuclear fusion: the joining together of two or more smaller nuclei to form a heavier nuclei of a new element. High temperatures and pressures are required to overcome the repulsion between the positive nuclei. This is the process which occurs in stars.

light and electrons...

Energy levels- electrons occupy fixed energy levels- these are the same for each atom of an element. In the ground state, electrons are closest to the nucleus and have the…

Comments

Wyne Neshava

so helpful thanx make more for developing fuels thanx again

Eleanor Rawsthorne


Its even better because you've done this one and a Developing Fuels one! life saviour. I get bored of that FAT text book :)

Similar Chemistry resources:

See all Chemistry resources »See all Acids, bases and salts resources »