BCM.01 - ATOMS

Relative isotopic mass

The weighted mean mass of an atom of an isotope compared to 1/12th the mass of an atom of Carbon-12.

Relative molecular mass

The weighted mean mass of a molecule compared to 1/12th the mass of an atom of Carbon-12

Relative atomic mass

The weighted mean mass of an atom of an element compared to 1/12th the mass of an atom of carbon-12

Atomic mass + unit

The mass of an isotope of an element ( Da )

Molar mass + unit

The sum of atoms, molecules, ions or other entities in one mole of a substance in grams (gmol-1)

Isotope

An atom of an element with the same number of protons but a different number of neutrons.

Mole

the mass of a substance that contains 6.023 x 1023 particles of the substance.

Dalton + value

1/12 of the rest mass of a carbon-12 atom 1.6605×10−27 kg

Proton, Neutron and electron shorts hands

p+

n0

e-

Specific charges on protons and neutrons

+/- 1.60 × 10-19 C

mass of a proton

1.67 × 10-27 kg

mass of a neutron

1.66 × 10-27 kg

mass of an electron

1/2000

9.11 × 10-31 kg

Summarise JJ Thompsons Model

If it were correct, describe the outcome of the gold foil experiment.

PLUM PUDDING MODEL

- Atoms are a ball of positive charge with tiny spheres of negative charge ( electrons ) within them, making the atom neutral.

- Alpha particles would barely be deflected due to the positive charge being diffuse and spread out over the whole volume of the atom.

Summarise Geiger/ Mardsen/ Rutherfords model of the atom

PLANETARY MODEL

- Positive charge is concentrated at the nucleus of the atom, with electrons revolving around this nucleus in free space.

Outline modelling subatomic interactions

- Nuclei and Alpha particle interaction can be modelled as particles. As particles have mass, momentum and velocity we can model them as small balls.

Outline the gold foil experiment and results

H/G/R fired alpha particles at a screen of gold foil and mapped their pathways with a detector screen.

Found very few particles were significantly deflected, suggesting they were coming close to a condensed source of positive charge and were repelled ( nucleus ).

They also suggested that if the alpha particle is fired parallel to the nucleus there is a region behind the nucleus that they can never enter ( shadow ).

Equation for density

mass/ volume

dilution equation

C1V1=C2V2

units of density

g.L-1

units of molarity

mol.L-1

1dm^3=

1L

Usage of H,C,N,O

Basic building blocks of life

Usage of S and P

Biochemicals - proteins and amino acids

Alkali metals ( Na, K ) and halogens (Cl)

Electrolytes

Signalling molecules

Transition elements ( Fe, Zn, Cu ) , Alkaline earth metals ( Ca, Mg ) and remaining non metals ( I, Se)

Trace amounts

Mg chlorophyll complex

Fe bones and blood

Other ( B, V, Si)

B cell walls

V nitrogen fixing bacteria

( Non essential in humans )

Why is nothing beyond Iodine used?

Elements heavier than Fe are scarce and can only be formed via supernova explosion

Give the isotopes of Hydrogen and their percentages

H1 ( Protium ) >99%

H2 ( Deuterium - Stable )

H3 ( Tritium - Radioactive )

Give the isotopes of Nitrogen and their percentages

N14 >99%

Give the isotopes of Oxygen and their percentages

O16 >99%

Give the isotopes of Carbon and their percentages

C12 99%

C13 1 % ( Used in NMR )

C14 ( Radiocarbon ) <1%

Elements close to Fluorine are ......

Metals are .....

Electronegative

Electropositive

Why is their more C12 in plant biomass than C13?

What can this be used for?

C12 diffuses into/ out of the stomata faster because it is lighter so is preferred. Used for finding biological origins of fossil materials.

Unstable Isotopes ..

decay exponentially

Equation for exponential decay

Half life, decay mode and applications of C14

5700 years

B-

Labelling

Half life, decay mode and applications of H3

12 yrs

B-

Dating <60,000 yrs

Half life, decay mode and applications of P32

14 days

B-

Labelling DNA/RNA

Half life, decay mode and applications of S35

88 days

B-

Labelling proteins

Half life, decay mode and applications K40

1.25 × 10^9 yrs

β− / e− capture + γ

Dating rocks

Half life, decay mode and applications U235

7.04 × 10^8 yrs

α / fission

Dating rocks / power