1 Atomic structure Flashcards
What is the mass of a proton?
One atomic mass unit
the atomic number of an element is equal to the number of protons found in an atom of that element
What are isotopes
each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element.
True or false? The charge of electrons is equal to that of protons
Trick question. It is equal in magnitude, but opposite in sign.
Give the three isotopes of hydrogen
Protium: 1 AMU, no neutrons
Deuterium: 2 AMU, 1 neutron
Tritium: 3 AMU, 2 neutrons
What is atomic weight?
In nature, almost all elements exist as two or more isotopes and these isotopes have consistent proportions in any sample of naturally occuring elements. The weighted average (weighted by proportionality) is referred to as the atomic weight.
This is the number reported on the periodic table.
Because half-life corresponds with stability, the isotope with the longest half-life is usually the most abundant and the atomic weight will be closest to this isotope’s mass.
How many particles of an atom does it take to make the atomic weight in AMU equal a sample’s mass in grams?
6.02 x 10^23 atoms
(Avogadro’s number).
What is the Planck relation and how can it be used to determine the energy of electromagnetic radiation from matter as quanta (discrete bundles of matter)
E = hf
E: energy
h: Planck’s Constant (6.626 x 10^-34 J*S)
f: Frequency of the radiation
What is the ground state of an atom?
The state of lowest energy in which all electrons are in the lowest possible orbitals.
An atom is said to be in an excited state when at least one electron has moved to a subshell of higher than normal energy.
As electrons go from a lower energy level to a higher energy level, they get AHED (absorbs light, higher potential, excited, distant from the nucleus)
How are atomic emission spectra created?
At room temp, the majority of atoms in a sample are in the ground state. However, electrons can be excited to higher energy levels by heat or other energy forms to yield excited states. The electrons will rapidly return to the ground state, however, emitting a discrete amount of energy in the form of photons.
These photons are fluorescence and have different wavelengths, which can be plotted on a line spectrum. Each element possesses a different atomic emission spectrum.
Wavelength of electron orbital transitions are inversely proportional to energy. Give the equation for this
E = hf = hc/λ
E = energy h = planck's constant f = frequency of the radiation c = speed of light (3 x 10^8 m/s) λ = wavelength of the radiation
The energy of the emitted photon corresponds to the difference in energy between the higher-energy initial state and the lower energy final state.
A positive E corresponds to emission, a negative E corresponds to absorption.
ΔE is the same for absorption or emission between any two energy levels according to the conservation of energy. To identify gaseous elements an absorption spectrum (not emission spectrum) must be used where specific wavelengths of light are used to excite electrons to a higher energy level.
What is the principle that states it is impossible to simultaneously determine with perfect accuracy the momentum and the position of an electron?
Heisenberg Uncertainty Principle
What is the Pauli exclusion principle?
No two electorns in a given atome can possess the same set of four quantum numbers (n, l, mp and ms)
The position and energy of an electron described by its quantum numbers are known as its energy state.
For a given value of n only certain values of l are permissible. For a given value of l only certain values of ml are permissible.
What are the four quantum numbers and what do they mean?
n: principal quantum number. The larger the integer value of n the higher the energy level and radius of the electron’s shell (Bohr model). Within each shell there is a capacity to hold a certain number of electrons, given by 2n^2
l: azumutahl (angular momentum) quantum number. Shape and number of subshells within ag iven principal energy level (shell). Important for bonding/bond angles. ‘
ml: magnetic quantum number. Specifies orbital within a subshell where an electron is most likely to be found. (ml = -l to +l, e.g is l=2 than ml = -2, . -1, 0, +1, and +2).
ms: spin quantum number. 2 electrons per orbital, one has ms = +1/2 and one has m= -1/2
What is the capacity of each shell orbital to hold a certain number of electrons? (formula)
2n^2
Where n is the principal quantum number
The difference in energy between two shells decreases as the distance from the nucleus increases
How do you determine how many subshells there are per energy level?
l can only be = 0 to (n-1)
n: principal quantum number.
l: number of subshells within a given principal energy level (n)
