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
As atomic number increases the number of neutrons in the nucleus tends to
increase much more rapidly than the number of protons to counteract the repulsion between protons in the nucleus.
What does the band stability show
The band of stability graph, also known as the belt of stability, shows the stability of an atom’s nucleus by plotting the number of protons on the x-axis and the number of neutrons on the y-axis. The graph shows where the nucleus is stable, which is indicated by a black squared line in the middle.
Isotopes to the left of the band of stability have high n/p ratios and decay by beta emission to move closer to the band
Isotopes to the top of the band with
atomic numbers larger than 84 tend to decay by alpha emission to move closer to the band
Whats a radioactive isotope
an unstable form of a chemical element that releases radiation as it breaks down and becomes more stable
What type of particle is emitted from alpha
helium nuclei (positively charged
particles
What can stop an alpha particle
Thin sheet of paper
What type of particle is emitted by Beta
electrons (negatively charged
particles) from nucleus
What can stop Beta
6 mm thick
aluminium foil
What type pf particle is emitted by gamma rays and what can stop them
very high frequency
electromagnetic radiation
thick lead sheet
What happens doing alpha decay
positively charged helium nucleus emitted
mass number decreases by 4
atomic number decreases by 2
What happens in Beta decay
negatively charged electron emitted from nucleus
Neutron is converted to a proton and an electron
Mass number remains the same
Atomic number increases by one
Who suggested that the wave-particle duality theory could also be applied to particles of matter
Louis de Broglie (in 1924)
What is probability density
the probability of finding the electron in a certain region of space the atom.
What is the atomic orbital
The volume of space in which there is a 95% chance of finding the electron
What is the principal quantum number n
the main energy level (or shell) of the electron
What is the angular quantum number l
the number of sublevels or subshells of n and the shape of the orbitals
What is the magnetic quantum number ml
the maximum number of orbitals
within a subshell
What is the spin quantum number ms
gives the clockwise or anticlockwise orientation of the electron in the
orbital.
It has values of +½ or -½
Each orbital can hold a maximum of two electrons
Every s subshell contains
one spherical s orbital
Every p subshell is split into
three degenerate (equal in
energy) dumbbell-shaped p orbitals
The p orbitals are at
right angles to each other along x, y, and z three-dimensional axes
How many orbitals does s have
1 orbital
How many orbitals does p have
3 orbitals
How many orbitals does d have
5 orbitals
The electrons are still described as occupying
several energy levels n=1, n=2, n=3
Each energy level is pictured as containing one or more
sublevels within it, denoted by the letters s, p, d, f
Within these sublevels are regions called
orbitals, s, px, py , pz
Each orbital can only hold a maximum of
2 electrons
What is electron configuration
The arrangement of the electrons of an atom in its shells and subshells
Knowing this arrangement assists
with understanding various chemical and physical properties of atoms, elements, and molecules
When empty, the 4s subshell is slightly
lower in energy than the 3d subshell
What is Aufbau principle
In a normal atom in the ground state, electrons are normally
arranged so that the energy is at a minimum. Electrons are added to an atom one at a time beginning with the orbital of
lowest energy
What is Pauli Exclusion Principle
No more than two electrons can occupy an orbital
What is Hund’s rule
Electrons fill degenerate orbitals one at a time with parallel spin before a second electron is added with opposite spin
How is the electron configuration normally written
The electronic configuration is normally written with the
principal quantum number (1, 2, 3,etc.) followed by the symbol for the subshell (s, p, d, f, etc.), and a superscript that shows the number of electrons in the orbital
What do we write the short form based from
on last noble gas
What are the three ways u can show electronic configuration
Electrons in boxes
energy diagram
electronic configuration
Elements in a group have similar
electronic configurations
and properties
E.g. outer electrons: Group I: ns1
,Group II: ns2 ,Group IV: ns2np2
How to write the electronic configuration of ions
use the number of electrons remaining in the atom after the ion has been formed
Example
So, for negatively charged ions (anions), there will be more electrons than for the neutral atom
Whereas for positively charged
ions (cations), there will be
fewer electrons than for the neutral atom
What are the special electronic configuration for the 1st row
transition elements
the empty 4s orbital is actually slightly lower in energy than the empty 3d orbitals and is filled first
What is the anomaly for the element with atomic number 24 (Cr)
Instead of having a full 4s orbital, one electron is moved to a 3d orbital to give a very stable half-filled d subshell:
[Ar]4s13d5
What is the anomaly for the element with atomic number 29 (Cu)
Again, instead of having a full 4s orbital, one electron is moved to a 3d orbital to give a very stable completely filled d subshell
[Ar]4s13d10
What are the first row transition elements
Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Manganese (Mn), Iron (Fe), Cobalt (Co), Nickel (Ni), Copper (Cu), and Zinc (Zn)
What is the special electronic configuration for transition metal ions
the 4s orbitals are filled first but are emptied first. Thus all the first row
transition metals form stable 2+ ions
How is the evidence for arrangement of electrons in shells and subshells of different energies provided
by data obtained for ionisation energies (IE) of atoms
What do successive ionisation energies provide evidence for
the numbers of electrons theorised to be present in the principle quantum shells (n = 1, n = 2, n = 3, etc.) for different atoms
First ionisation energies provide evidence supporting
the existence of subshells s, p, d, f, etc.
What is first ionisation energy
the energy required to remove one electron from each atom in one mole of atoms of an element in its gaseous state to form one mole of gaseous ions.
The value of first ionisation energy depends on?
– Size of nuclear charge
– Distance of the outer electrons from the nucleus (i.e. atomic
radius)
– Shielding or screening effect of inner electrons
What is the effect of nuclear charge
Going from left to right across any period in the periodic table
protons increases -> nuclear charge increases -> greater attractive force between the nucleus and outer electrons -> more energy needed to remove an outer electron -> ionisation energy increases
What is the effect of Outer Electron Distance (Atomic Radius)
Going from top to bottom down any group in the periodic table
shells increases -> atomic radius increases -> greater distance between the nucleus and outer electrons -> smaller attractive force between the nucleus and outer electrons -> less energy needed to remove an outer electron -> ionisation energy decreases
Effect of inner electron shielding
shells increases -> # inner electron shells increases -> smaller effective nuclear charge felt by outer electrons -> smaller attractive force between the nucleus and outer electrons -> less energy needed to remove an outer electron -> ionisation energy decreases
Going from top to bottom down any group in the periodic table:
shells increases -> # inner electron shells increases -> smaller effective nuclear charge felt by outer electrons -> smaller attractive force between the nucleus and outer electrons -> less energy needed to remove an outer electron -> ionisation energy decreases
From left to right across a period
Ionisation energy increases
Down a group
ionisiation energy decreases
Why does IE value fall at the start of a new period
Because a new outer shell is added
Why is boron B 1st IE lower than beryllium be, when it has a greater nuclear charge than beryllium
This can be explained by the shift from the outer electron being in the s subshell in B to the p subshell in Be
The anomaly in 1st IE on going from Group II to Group III supports the theorised existence of s and p subshells
Why is Oxygen O, 1st IE lower than nitrogen N, when it has a greater nuclear charge than Nitrogen
This can be explained by the shift from the outer electrons in the p
subshell being unpaired in N versus pairing of electrons in the p subshell beginning in O
The anomaly in 1st IE on going from Group V to Group VI supports
the theorised arrangement of electrons in p subshells
What are successive ionisation energies
The energies associated with
removing additional electrons from the atom one by one.
What is the first electron affinity
The first electron affinity of an element is the energy absorbed
when one mole of gaseous atoms accepts one mole of electrons to
become ions. It has a negative value showing that in fact energy is
given out
What is Second electron affinity
The second electron affinity of an element is the energy absorbed
when one mole of gaseous atoms with a single negative charge
accepts one mole of electrons. It has a positive value showing that
in fact energy is taken in to counteract electronic repulsion between the incoming electron and the negative ion
