SNS - General Chemistry - Atomic Structure Flashcards
Heisenburg Uncertainty Principle
States that it is impossible to determine, with perfect accuracy, the momentum and the position of an electron simultaneously. If the momentum of an electron is being measured accurately, its position will change and vice versa
Quantum Numbers
Any electron in a atom can be descibed completely in terms of four quantum numbers:
- Principal quantum number, n
- Azimuthal quantum number, l
- Magnetic quantum number, ml
- Spin quantum number, ms
Pauli Exclusion Principle
No two electrons in a given atom can possess the same set of four quantum numbers
Energy State
The position and energy of an electron as described numbers
Quantum Numbers
n
Principal quantum number
Describes the size of the orbital
Quantum Numbers
n
Integer Values
Can theoretically take on any positive integer value
The larger the value, the higher the energy level and the radius of the electron’s orbit
Quantum Numbers
n
Maximum number of electrons in energy level n
2n2
Quantum Numbers
n
Relationship between difference in energy levels between adjacent shells and distance from the nucleus
Decreases as distance from the nucleus increases since it is related to the expression 1/n22 - 1/n12
Quantum Numbers
l
Azimuthal quantum number
Describes the shape of the orbital
Refers to the subshells that occur within each principal energy level
Quantum Numbers
l
Integer Values
For any given n, can be any integer between 0 and n-1
The four subshells corresponding to l = 0, 1, 2 and 3 are known as s, p, d and f subshells respectively
The greater the value, the greater the energy of the subshell, however the energies of subsheels from different principle energy levels may overlap. For example, the 4s subshell will have a lower energy than the 3d subshell as its average distance from the nucleus is smalller
Quantum Numbers
l
Maximum number of electrons within a subshell
4l + 2
Quantum Numbers
ml
Magnetic quantum number
Describes the orientation of an orbital
An orbital is a region within a subshell that may contain no more than two electrons. The magnetic quantum number specifies the particular orbital within a subshell which has a high probability of containing an electron at a given point in time
Quantum Numbers
ml
Integer Values
The possible values are all integers from l to -l including 0
Quantum Numbers
ml
Integer Values
L values and Orbitals
- s subshell
- p subshell
- d subshell
- f subshell
- l = 0, orbitals: 1 - 2 electrons
- l = 1, 0, -1, orbitals: 3 - 6 electrons
- l = 2, 1, 0, -1, -2, orbitals: 5 - 10 electrons
- l = 3, 2, 1, 0, -1, -2, -3, orbitals: 7 - 14 electrons
Quantum Numbers
ms
Integer values
Spin quantum number
+1/2 and -1/2
Quantum Numbers
ms
- Parallel Spins
- Paired electrons
- Electrons in different orbitals with the same ms values
- Electrons with opposite spins in the same orbital
Electrons Configurations:
- Nitrogen
- Iron
- Z = 7. Thus electron configuration is
↑↓ ↑↓ ↑↑↑
1s² 2s² 2p³
- Z = 26
↑↓ ↑↓ ↑↓↑↓↑↓ ↑↓ ↑↓↑↓↑↓ ↑↓ ↑↓↑↑↑↑
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶
Z and A
- Z - atomic number
- A - mass number
Determine the number of protons, neutrons and electrons:
- Nickel-58
- Nickel-60 2+ cation
- A = 58, Z = 28: protons = 28, electrons = 28, neutrons = (58 - 28) = 30
- A = 60, Z = 28: protons = 28, electrons = (28 - 2) = 26, neutrons = (60 - 28) = 32
Atomic mass vs atomic weight
Atomic mass - relative mass of an atom compared to the mass of a carbon-12 atom. Expressed in amu, where one amu is equal to exactly 1/12 the mass of a carbon-12 atom
Atomic weight - weight in grams of one mole of an element (contains 6 x 1023 particles)
Find the atomic weight of element Q which consists of three different isotopes: A (40 amu, 60% naturally occuring Q), B (44 amu, 25%), C (41 amu, 15%)
= (0.6 x 40) + (0.25 x 44) + (0.15 x 41)
= 41.15
Electrons Configurations:
- Chromium
- Copper
- 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d5
- 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰
- Paramagnetic
- Diamagnetic
The presence of unpaired or paired electrons affects the chemical and magnetic properties of an atom or molecule.
- If a material has unpaired electrons, a magnetic field will align the spins of these electrons and weakly attract the atom
- Materials that have no unpaired electrons and are slightly repelled by a magnetic field are said to be diamagnetic
Valence Electrons
- Group IA
- Group IIA
- Groups IIIA - VIIIA
- Transition elements
- Outermost s electrons
- Outermost s electrons
- Outermost s and p electrons
- Outermost s, d of next-to-outermost shell, f of shell two below outermost shell
Valence Electrons
- Elemental iron
- Selenium
- Sulphur atom of sulphate ion
- 8 valence electrons: 2 in 4s, 6 in 3d
- 6 valence electrons: 2 in 4s, 4 in 4p. Selenium’s 3d electrons don’t form part of its valence shell
- 12 valence electrons: original 6 (3s2, 3p4) plus 6 more from the oxygens to which it is bonded. Sulphur’s 3s and 3p subshells can only contain 8 of these. The rest have entered the sulphur atom’s 3d subshell which in elemental sulphur is empty
Atom
Smallest representative particle of an element. Composed of protons, neutrons and electrons
Proton
Positively charged subatomic particke found in the nucleus
Neutron
Electrically neutral subatomic particle found in the nucleus. Has approximately the same mass as a proton
Electron
Negatively charged subatomic particle found outside the nucleus. Has a mass of ~1/1836 that of a proton
Valence principal energy level
Refers to the electron population of the outer principal energy level. This number is important as these electrons come into contact with other atoms when forming compounds. In the periodic table, the elements in each column have the same number of valence electrons
Electron configuration
Refers to the arrangement of electrons in an atom. In the most stable configuration of an atom, the electrons are in their lowest possible energy state (ground state)
Principal energy level
Or shell. Each principal energy level within an atom contains one or more sublevels (or subshells)
Lewis dot diagram
Shows an element surrounded by a series of dots which represent the valence electrons of the element
Atomic Orbitals
Each has no more than two electrons of opposite spin
Principal quantum number, n
Denotes an electron’s energy level. It is related to the average distance of the electron from the nucleus. The number n can have any positive integer number. The larger it is: 1. The farther the distance between the nucleus and the electron 2. The larger the average energy of the levels belonging to the shell 3. The less the difference in energy between adjacent shells (eg 5 is less different to 6 than 2 frm 3) The maximum number of electrons in elergy level n is expressed 2n^2
Azimuthal quantum number, l
This shows the angular momentum magnitude. Each shell is composed of one or more subshells designated as l.The number of subshells for a shell is equal to the value of n. The value of l may be 0 to n-1. For example, if a shell has three subshells, n=3 and the l values are 0, 1 and 2. Letters are associated with the l values as follows: 0=2, 1=p, 2=d, 3=f
Magnetic quantum number, ml
Tells us the angular momentum orientation. This is the orientation of an orbital in space. The values of ml are all integers from -1 to +1
Spin quantum number
Tells us the electron spin direction. Its values are + or - 1/2. The significance of the spin is explained by the Pauli exclusion principle which states that in a given atom no two electrons can have exactly the same quantum numbers. Each orbital can be filled by only two electrons and the electrons can spin in only two directions: + spin and - spin
Order of orbital sequencing
Electrons fill sublevels starting with the lowest energy level first following the fbelow order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 7s, 5f, 6d…
Maximum numbers of electrons -s sublevel
2
Maximum numbers of electrons -p sublevel
6
Maximum numbers of electrons -d sublevel
10
Maximum numbers of electrons -f sublevel
14
Electron Configurations Simplifying Using Noble Gases
Often an abbreviated version is used o simplify the electronic configuration. Inner electrons are represented by a noble gas and valence electrons are written in electronic configuration. For example iron: Fe = 1s1 2s2 2p6 3s2 3p6 4s2 3d6 Fe = [Ar] 4s2 3d6
Electron Configurations Hund’s Rule
States that for degenerate orbitals, the lowest energy is acheived when the number of electrons with the same spin is maximised
