WEEK 1 Flashcards
To maintain precision while solving any mathematical equation involving
numbers…
calculations and answers should always be reported in the same number of significant figures as that of the input variables provided
sig fig rules!
- All non-zero digits are significant
- Zeros appearing between any two non-zero digits are significant
- Leading zeros are not significant
- Trailing zeros in a number containing decimal point are significant
what is a unit?
provides measure to the numerical quantity associated with it
what are the fundamental units for distance and time respectively
metres (m) and seconds (s)
what are fundamental units?
units for physical quantities from which all other units can be generated
SI system fundamental units
kilogram (kg), metre (m), candela (cd), second (s), ampere (A), kelvin (K) and mole (mol)
Newton (N)
unit for force is composed of combination of fundamental units : kg m s-2
force (N) = mass (kg) x acceleration(ms^-2)
Joules (J)
unit for energy is composed of combination of fundamental units : kg m2 s-2
energy (J) = force (kg ms^-2) x distance (m)
Nucleogenesis
formation of new nuclei from existing nucleons
Nuclides
an atom with a particular mass number and atomic number
Isotope
nuclide with the same atomic number but a different mass number
exothermic
releases energy into surroundings as heat and radiation
every atom is generated…
from the simplest nuclide hydrogen by nuclear reactions
hydrogen burning
The star continues to burn H until it exhaust all H atoms, then begins to burn He to for increasingly larger atoms
New element-forming reactions are exothermic until iron
All elements up to iron are produced in stars
When a star has only iron to burn, it consumes energy and implodes, forming a supernova.
The decay constant (k)
is characteristic of the particular radioactive nuclide, and does not depend on the amount of sample.
A low activity corresponds to a
small decay constant + long half-life
A high activity corresponds to a
large decay constant + short half-life
Radiocarbon dating
- Measure the *C-14 activity *of the archaeological sample (This is At)
- Measure the C-14 activity of an equivalent modern-day sample (this is A0)
- Substitute these values into the equation for C-14 age:
t = 8033 x ln(A0/At)
Within a star…
clouds of atomic hydrogen are pulled together by gravity and heat as they are compressed. When temp rise high enough, the cloud ignites as a star.
balancing nuclear reactions
both the mass numbers and atomic numbers must balance
Atomic number (Z)
= number of protons in the atomic nucleus
* Defines chemical nature (element) of the atom
* Equal to the total charge on the atomic nucleus
Mass number (M)
= total number of nucleons (protons and neutrons) on the atomic nucleus
Atomic mass
Atomic mass of an element is the average of the atomic masses and the abundances of each of the naturally-occurring isotopes
Hydrogen fusion
energy comes from a change in mass, according to E=mc^2
Radioactive Atomic Nuclei
Undergo spontaneous decay to eventually become a stable nucleus
will have a characteristic mode of decay and half-life
Half-life
the time required for half of the nuclei in a sample to undergo a decay event
The rate of decay…
depends on the number of nuclei present
activity (A)
Activity A of a radioactive sample is a specific measure of the rate of decay, defined as the number of nuclei that disintegrate per second
This unit of activity is the Becquerel
1 Becquerel = 1 disintegration per second
Activity is proportional to the number of nuclei in the sample
Specific activity
activity per gram of radioactive nuclide
Molar activity
activity per mole of radioactive nuclide
Anion
gained electrons so have a negative charge
n more electrons than protons
Cation
lost electrons so have a positive charge
n fewer electrons than protons
