Atomic structure Flashcards
What is element
1) Substances that cant be broken down into simpler substances by a chemical reaction
Dalton model of atoms
1) observed in 19th century
2) First person to assign chemical symbols to element s
3) We can understand how elements react together to make new substances called compounds .
4) he noticed elements always combine in fixed ratios
What did JJ Thomson model suggested ?
1) Electrons are part of atoms
2) He observed stream of - charged electrons, when high voltage was applied to a metal
3) Due to neutrality of atom, he suggested that electrons must be scattered in a positively charged sponge like substance.
Rutherford’s model of an atom
1) he tested Thomson’s model.
2) he fired alpha particles at a piece of gold foil
3) Alpha particles= helium nuclei.
4) If Thomson’s model was true then large number of particles should have passed straight through or get stuck in the positive sponge.
5) Most of the alpha particles did pass through but some were repelled and bounced back
6) Large no of deflected particles led to the conclusion that atom is mainly empty space.
7) Large deflections= + alpha particles collide with and are repelled by a dense , + charged nucleus
8) small no of alpha particles bounced back= nucleus is very small.
What is the relative mass of electron
5 X 10^-4
Bohr model of hydrogen.
1) pictured H atoms as a small solar system
2) The electrostatic attraction between the sub atomic particles prevent the electron from leaving the atom.
3) Without neutrons, protons would repel each other and nucleus would fall apart.
4) An electron moves into an orbit or higher energy level further from nucleus when an atom absorbs energy.
What does Z represent ?
1) Atomic number
2) No of protons.
What does ‘A’ represent ?
1) Mass number
2) Protons+neutrons.
What are isotopes
Atoms of same element with different mass numbers.
1) Similar chemical properties
2) Difference in mass lead to different physical properties.
What is relative atomic mass
average mass of an atom of the element taking into account all the isotopes and their relative abundance, compared to one atom of Carbon-12.
What does no of lines represent in mass spectrum ?
No of isotopes present
Does all electromagnetic radiations travel at the same speed (c)
YES
Wavelengths of different colors of visible light
Red light>orange > yellow> green> blue> pink.
Increasing wavelength of electromagnetic spectrum,
Gamma rays< X-rays < UV< visible light< IR < Mirco waves< radio waves
Absorption spectrum
shows the radiation absorbed as atoms move from a lower to higher energy level.
Emission spectrum
when an atom moves from a higher to a lower level.
How much energy is released for one transition ?
1 photon (packet of energy) is released for each electron transition.
Why line emission spectrum is not quantized ?
1) electron cant change their energy in continuous way
2) it can only change its energy in discrete amounts. +
Different electromagnetic radiations related to energy levels
When electrons fall to
n=1 — UV radiations are released = Lyman series
n=2—- Visible light= Balmer series
n=3—- IR radiations or higher energy levels= Paschen series.
Disadvantages of Bohr model
1) Failed to predict the spectral lines of atoms with more than one electron
2) Assumes electrons trajectory can be precisely described- which is impossible
What is Heisenberg uncertainty principle ?
We cant know where an electron is at any given moment in time.
what are atomic orbitals ?
1) Solution to Schrodinger wave equation
2) Region around an atomic nucleus in which there is a 90% probability of finding the electron.
Whats the difference between 3 2p orbitals
1) Only orientation in space
2) They have same energy
Confusion between the energy of 3d and 4s
3d falls below 4s for elements with atomic number greater than 20
