Autumn semester Flashcards
How is the periodic table arranged?
Elements are sequenced in increasing atomic number across the periods, and arranged so that elements with similar chemical properties fall in the same groups.
What are the sap,d,f blocks of the periodic table?
s-block = groups 1-2
p-block = 13- 18
d-block = 3-12
f block = bottom part
What is the composition of an atom?
The atom consists of negatively charged electrons which move around a central nucleus containing positively charged protons and neutrons.
What is an isotope?
An isotope are elements with the same atomic number but have different mass numbers (differ with amount of neutrons)
What is the octet rule in relation to the driving force for reactions?
The octet rule states that atoms will continue to share electrons until they have acquired an octet of valence electrons. The driving force of any reaction is the formation of the electronic structure of a noble gas.
Each orbital contains maximum 2 electrons where there is 1 s orbital, 3 p orbitals, five d orbitals and 7 f orbitals.
What is the concept and importance of the valence shell?
The valence shell is the highest energy set of orbitals that contain the outer (valence) electrons. It is important as it is the orbital that is gaining or losing electrons.
How do you identify valence electrons for an element and why are they important?
Valence electrons are the electrons listed after the last noble gas configuration (outer electrons)
Valence electrons are important is chemistry as in an ionic compound is tell us the oxidation state and number of bond formed.
How is the structure of the atoms found in experiment?
Rutherford > conducted an experiment in which alpha (HE2+)particles where shot through a gold foil. He found that he vast majority of the ions went straight through with minimal scattering (proving high amount of space between electrons) however some where reflected back at large angles suggesting there presence of a larger charged mass (the nucleus).
Additional he tried to use classical mechanics to explain atom behaviour, this failed as the electrons gradually decayed and collided with nucleus.
Bohr > suggested that energy of an electron in a particular orbital was quantised, he proved this by exciting hydrogen particles which showed shared bands of light emitted showing well defined gaps.
What is the concept of energy levels around an atom?
Electrons located around an atom are found in defined area called energy levels, they represent the 3d space surrounding an atom where electrons are most likely to be.
What is the definition of ionisation energy?
Ionisation energy is the amount of energy needed to remove 1 electron from an atom. The ionisation energies where found to agree exactly with those measured experimental in the atomic spectrum of hydrogen.
What is electromagnetic radiation?
A from of energy consisting of oscillating electric and magnetic fields which travel at the speed of light (c).
e.g visible light, microwaves, x-rays … ( they all have wavelengths)
What is the equation relating to frequency, wavelength and velocity of light?
λv = c
λ = wavelength (m)
v = frequency (Hz/s^-1)
c = speed of light (2.998 x 10^8 m/s)
How does flame test observations relate to atomic structure?
The flame test is used to visually determine the identity of an unknown metal or metalloid ion based on the characteristic color the salt turns the flame of a bunsen burner. The heat of the flame converts the metal ions into atoms which become excited and emit visible light. The colour emitted corresponds with the energy change of the gaps between energy levels.
What is a photon?
In some situation it was found that the behaviour of light/radiation cannot always be thought of as waves but instead particles. Max Planck proposed that electromagnetic radiation could only be emitted and absorbed in quanta of radiation called photons.
The energy of a photon is proportional too its frequency.
What is the equation relating the energy of a photon to frequency?
E = hv
E = energy (j)
h = planck’s constant (6.63 x 10^-34 js)
v = frequency (Hz or s^-1)
What is the photoelectric effect?
The ejection of electrons from a material pm irradiation by light (Light hits the material and electrons are thus displaced).
The electrons are only ejected from the surface is the frequency of the radiation is above a threshold value called the work function.
How is the photoelectric effect applicable in the phototube?
a vacuum tube containing a cathode made of a metal with a small work function so that electrons would be easily emitted. The current released by the plate would be gathered by an anode held at a large positive voltage relative to the cathode
What is the de Broglie relationship and how is it used?
De Broglie pointed out that the energies calculated for a wave and for a particle must be equal for anything behaving as both showing wave-particle duality.
λ = h/p
λ = Wave length (m) (limiting factor)
h = Planck’s constant (6.63 x 10^-34 js)
p = momentum of particle (mass x velocity)
What is the uncertainty principle?
As an electron has wave-like properties with wave length = order of magnitude of the size of an atom, you can determine the probability that an electron is in a certain place.
What is the Heisenberg uncertainty principle?
An electron has a position in space defined by x,y,z coordinates and has a momentum (p=mv) parallel to each axis (px,py,pz)
thus :
ΔxΔpx ≥ h / 4π
Where Δx, Δpx are the uncertainties in measuring x and px, we can know the position of an electron thus the less we know about its momentum (and vis versa).
Example of the Heisberg uncertainty: calculate the minimum uncertainty in the position of an electron (mass = 9 x 10^-31 kg) moving at 3 x 10^5 m/s with an uncertainty in the velocity of +/- 10^2 m/s?
Δx = h / 4π x Δpx
Δpx = mass x velocity
= (6.63 x 10^-34) / 4π x ((9x10^-31)x(2x10^2)) = 293 nm
What is the concept of a wave function and why is it used?
The wave function tell us how likely an electron is in a particular location at a given time its denoted by the symbol 𝚿 (psi). It is calculated using Schrodinger equation.
What is the physical significance of the wave function?
Max Born suggested that the probability of finding a particle in any region of space is proportional to 𝚿^2.
Thus in a region were 𝚿^2 is large, the probability of finding and electron is high and vis versa.
(𝚿 = 0 there is a node)
What is the Schrodinger equation?
Schtodinger used wave function to produce a mathematical equations to calculate the behaviour of an atom however it can only be solved for two body problems ( a system containing only a nucleus and an electron).
H𝚿 = E𝚿
𝚿 = R (r)Y (θ, Ф)
n,l l,ml
R =