Atomic Structure Flashcards
The foundation of chemical research is based on?
Experiments and Explanations
What is an experiment ?
An experiment is an observation of natural phenomena carried out in a controlled manner so the results can be duplicated and rational conclusions obtained
What is a hypothesis?
A hypothesis is a tentative explanation of some regularity of nature
What is a theory
A theory is a tested explanation of basic natural phenomena
What does it take for a theory to be commonly accepted in society?
Good fit between the evidence and theoretical constructs
Reliability and Accuracy of data
Replicability of experiments including by other researchers
Consensus within the scientific community
What is a law?
A law is a concise statement or mathematical equation about a fundamental relationship or regularity of nature
What is the general process of advancing scientific knowledge through observation, the framing of laws, hypotheses or theories; and the conduction of more experiments called?
The Scientific Method
In what year did Dalton come out with his theory about the atom?
1807
What did Dalton’s theory entail
He conceptualized that all matter was made of atoms that are different for different elements and atoms were hard spheres.
What are the Assumptions/ postulates of Dalton’s atomic theory?
Matter consist of tiny particles called atoms which are indestructible and indivisible
All atoms of the same element are identical in mass and chemical properties. They differ from the atoms of other elements
Atoms can combine in simple whole number ratios to form compounds
A chemical reaction consists of rearranging atomsfrom one
combination into another. Atoms are not created, destroyed, or
broken into smaller pieces by any chemical reaction
What are some evidence for Dalton’s Model
The previously theorised law of conservation of mass: “the total mass remains constant during a chemical reaction” was supported by Dalton’s atomic theory
The previously theorised law of definite proportions (or constant composition): “a pure compound, whatever its source, always contains definite or constant proportions of the elements by mass
Dalton’s atomic theory predicted the law of multiple proportions: “when two elements form more than one compound, the masses of one element in these compounds for a fixed mass of the other element are in ratios of small whole
What are some Inaccuracies/Problems with Dalton’s Model
Atoms were later found to consist of further particles
Atoms can be destroyed by nuclear reactions
Atoms of the same element can have different masses example being isotopes
What year did J.J. Thompson come out with his theory
1897
What did J.J Thomson’s theory entail
J. J. Thomson conducted experiments that suggested that
atoms were not indivisible hard spheres but in fact were
comprised of smaller charged subatomic particles
What experiment did J.J Thomson carry out
Discharging electricity through gases at low pressure
When electricity was discharged through gases at low
pressure, cathode rays were found to be deflected by electric
and magnetic fields in a manner than indicated the presence
of negatively charged components
What did Thompson discover in the atom
Electrons
What is meant by Thompson’s Plum pudding model?
the atom has negatively charged electrons embedded in a sea of
positive charge
What are the problems/inaccuracies with Thompson’s Model
This model could not explain the deflection of alpha particles by metal foil
What year did Rutherford come with his theory
1909
What does Rutherford’s theory entail?
the atom must consist of
* mainly empty space with
* mass & positive charge concentrated (>99.5%) in tiny central nucleus
* while negatively charged electrons orbit the nucleus (like planets orbiting the sun)
What was Rutherford’s Experiment
Ernest Rutherford directed Geiger and Marsden to bombard
thin metal foils (e.g. gold) with alpha particles. Alpha particles
are positively charged.
– Most of the alpha particles passed through with no interaction
– However, a few ~ 1 in 8000 were scattered at large angles; some
were sent backwards towards the source
What is meant by Rutherfords planetary model
negatively charged electrons orbiting a positively charged nucleus
What are the Inaccuracies/Problems with Rutherford’s Model
If electrons are negatively charged, and the nucleus is positively charged, why don’t the electrons spiral into the nucleus?
Could not explain atomic and emission spectra, i.e. why do
atoms absorb or emit light of certain frequencies?
What is the photoelectric effect
The photoelectric effect is the ejection of electrons from the
surface of a metal or another material when light shines on it.
Electrons only receive enough energy to be ejected when the
frequency of the light exceeds a certain threshold value characteristic of the particular metal
Who came up with the wave particle theory?
Albert Einstein theorised that light has both wave and particle properties to explain the photoelectric effect
What are some factors that affect if electrons will be ejected? (Photoelectric effect)
Increasing the intensity of lower frequency light does not cause any electrons to be ejected
Increasing the intensity of light at the threshold frequency causes more electrons of the same energy to be ejected
Shining light at frequencies above the threshold frequency causes higher energy electrons to be ejected
What explains the Photoelectric Effect?
A particulate theory of light explains that If light consists of particles (called photons) then only those photons with the right energy (and thus frequency) can cause
an electron of a particular energy to be ejected. Increasing the intensity of light of the wrong frequency/energy would have
no effect
What is Max Plank’s Equation?
E = hv links the wave and particle properties of light, where E is the energy of a light particle (photon) and v is the frequency of the associated wave
When did Bohr come out with his theory
1913
What did Niels Bohr theory entail
Niels Bohr theorised a Quantum theory based model of the atom based on Max Planck’s suggestion that in certain systems energy
can be absorbed or emitted in certain specific amounts in separate packets of energy called ‘quanta
Bohr applied this to the atom & postulated the existence of discrete
energy levels within the atom, i.e. electrons can only orbit the nucleus at certain distances depending on energy
What are the features of the Bohr Model
Electrostatic force between nucleus & orbiting electrons cancelled out by outward force due to orbital motion [so electrons do not spiral into the nucleus]
Electron in a given orbit can only have a certain amount of energy (i.e. the energy is quantized) & the orbit can only have a certain radius
If the electron absorbs a “quantum” of energy (a photon of light energy), it moves to an orbit with a higher energy level that is further away from the nucleus. It is in an “excited” energy state
An excited electron emits energy to return to its stable “ground state” orbit
For an electron to move from an orbit E1 to one of energy E2
,the light absorbed must have a frequency given by Planck’s Equation ∆E = hv
Bohr assigned quantum numbers to the orbits eg n=1
What are some evidence for Bohr’s Model
Atomic Absorption, Emission Spectra and Hydrogen Emission Spectrum
What are the Inaccuracies/Problems with the Bohr Model
Explained the emission spectrum of a simple atom like hydrogen, but failed to explain the spectra of more advanced atoms
What did Goldstein (1900) and Moseley (1913) contribute to atomic theory
-detected protons as separate
entities
– theorised that since atoms are neutral # protons = # electrons
– theorised that since the mass of the electron is negligible and the
mass of the protons adds up to less than the total mass of the atom
→ neutrally (zero) charged particles (i.e. neutrons) must exist
What did Chadwick (1932) contribute to atomic theory
– experimental detection of the neutron
– bombarded Be with alpha particles
– produced a stream of neutrally charged particles that had enough
mass to pass through several cm of solid lead → neutrons detected
What did Schroedinger (1926) contribute to atomic theory
– applied deBroglie’s wave-particle duality theory to electrons
– atomic orbitals described in terms of probability densities
– suborbitals of electrons theorised
What did Louis de Broglie (in 1924) suggest in Wave particle Duality
He suggested that the wave-particle duality
theory could also be applied to particles of matter
What can be used to determine relative atomic mass of an element
Mass Spectrometry
