Mass number
sum of number of protons and neutrons in the nucleus
Atomic number
number of protons in the nucleus. since atoms are electrically neutral, the number of protons is also equal to the number of electrons
Isotope
Atoms of the same element with the same number protons but with a different number of neutrons
Carbon - 14
- used to estimate the age of organisms
-process is called carbon dating
-these isotopes are very penetrating and can be used to treat cancer cells
Cobalt -60
- a powerful gamma emitter, making it useful treatment for cancer
- also been used to stop the immune response to transplanted organs in the body
- also used in levelling devices and to sterilize food and spices
Iodine 131/ Iodine 125
-131 releases both gamma and beta radiation
- can be used to treat thyroid cancer and detect if the thyroid is functionally correctly
-thyroid will take up the iodine and the radiation will kill part of it
- 125 is a gamma emitter can can treat prostate cancer and brain tumours.
Mass spectrometry
- instrument that can be used to measure the individual masses of atoms.
- separates individuals isotopes from a sample of atoms and determine the mass of each isotope.
Operation of mass spectrometer:
- Vaporization: The sample is heated and vaporized, and passed through into an evacuated tube
- This separates the particles
- Ionization: The atoms/molecules are then bombarded by a stream of high energy electrons, knocking electrons off the particles, resulting in ions with a 1+ charge
- Acceleration: The positively charged ions are then accelerated along the tube by means of the attraction to negatively charged plates. The ions pass through the slits, which control the direction and velocity of their motion
- Deflection: The ions are then passed into a very strong magnetic field, deflecting the ions in a curved path
- Detection: The ions are detected electronically by a device that measures the location and the number of particles
Deflection in a mass spectrometer dependent
- absolute mass of the ion
-charge of the ion
-strength of magnetic field
-velocity of ions
Calculation relevant atomic mass
A_r=((relative isotopic mass_1×%abundance_1 )+(relative isotopic mass_2×%abundance_2 )+⋯)/100
Bohr Model main ideas:
- Electrons orbit the nucleus in ring like paths around the nucleus at fixed energy levels. The higher the energy level the farther away the electron is from the nucleus and the higher the energy
- Orbits further from the nucleus exist at higher energy levels
- Bohr said that electrons are quantized, meaning electrons can only occur in one energy level or another but nothing in between. The ground state is the energy level an electron normally occupies
- Electrons can only move from one orbital to another orbital at one time. When electrons absorb energy they move up to a higher energy level. This is called the excited state. When the electron returns to a lower energy level they emit energy. These emissions are not always visible to the naked eye
Emission Spectrums
- Emission spectra are produced when photons are emitted from atoms as excited electrons return to a lower energy level
- Each electron transition from a higher energy level to a lower energy level corresponds to radiation with a specific frequency or wavelength
- Emission (line) spectrums are produced by excited atoms as they fall back to a lower energy level and only contain specific colors (wavelengths, frequencies) of visible light
- Every element has its own unique emission (line spectrum). Hence, an element can be identified from its emission spectrum
- Ultraviolet light is produced when electrons drop to the first energy level (Lyman series)
- Infrared is produced when electrons drop to the third energy level (Paschen series)
Hydrogen emission spectrum
*The line emission spectrum of hydrogen provides evidence for the existence of electrons in discrete energy levels
* The energy of the lines on the emission spectrum of hydrogen corresponds to the difference in energies between energy levels
* Every element has its own unique emission (line spectrum). Hence, an element can be identified from its emission spectrum
* The Balmer series is the name given to a series of spectral emission lines of the hydrogen atom that result from electron transitions from higher levels down to the energy level where n=2
Electromagnetic spectrum
- All electromagnetic waves travel at the same speed, but can be distinguished by their wavelengths
- A smaller wavelengths has a higher frequency, so possess more energy
- A larger wavelength has a lower frequency, so posses less energy
- To sum, as energy increases so does the frequency. So red light has lower energy than violet light which is why UV light is so damaging to the skin, since high energy is more dangerous than low energy
- The electromagnetic spectrum shows the range of all possible frequencies of electromagnetic radiation
wavelength
o A wavelength is the distance between two successive crests
order of electromagnetic spectrum
The order of the spectrum is radio, microwave infrared, visible, ultraviolet, x-ray and gamma ray
Paulis exclusion principles
no more than two electrons can occupy any one orbital and if two electrons are in the same orbital they must spin the oppisite way
Aufbau principles
electrons are placed into orbitals of lowest energy’s first
Hund’s third rule
orbitals of the same sub-level are filled singly first, then doubly. if more than one orbital in a sub level is available electrons occupy different orbitals with parallel spins.
First ionization energy
The minimum amount of energy required to remove one mole of electron from one mole to gaseous atoms to another
Factors that influence ionization energy
- Size of the nuclear charge
- Distance of outer electron from the nucleus
- shielding effect
Size of the nuclear charge
Size of the nuclear charge
* As the atomic number (number of protons) increases, the nuclear charge increases
* The larger the positive charge, the greater the attractive electrostatic force between the nucleus and all the electrons
* a larger amount of energy is needed to overcome these attractive forces and remove an electron
* As the proton number increases, ionization energy increases:
Distance of outer electrons from the nucleus
- The force of electrostatic attraction between positive and negative charges decreases rapidly as the distance between them increases
- Hence electrons in shells (main energy levels) further away from the nucleus, are more weakly attracted to the nucleus than those closer to the nucleus
- The further the outer electron shell is from the nucleus, the lower the ionization energy
- Thus, ionization energies tend to decrease down a group of the periodic table
Shielding Effect
- Since all electrons are negatively charged, they repel each other
- The full inner shells of electrons prevent the full nuclear charge being experienced by the outer electrons.
- The greater the shielding of outer electrons by the inner electron shells, the lower the electrostatic attractive forces between the nucleus and the outer electrons
- The ionization energy is lower as the number of full electron shells between the outer electrons and the nucleus increases
