SNS - General Chemistry - Atomic Structure

Question 1

Heisenburg Uncertainty Principle

Answer 1

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

Question 2

Quantum Numbers

Answer 2

Any electron in a atom can be descibed completely in terms of four quantum numbers:

1. Principal quantum number, n
2. Azimuthal quantum number, l
3. Magnetic quantum number, ml
4. Spin quantum number, ms

Question 3

Pauli Exclusion Principle

Answer 3

No two electrons in a given atom can possess the same set of four quantum numbers

Question 4

Energy State

Answer 4

The position and energy of an electron as described numbers

Question 5

Quantum Numbers

n

Answer 5

Principal quantum number

Describes the size of the orbital

Question 6

Quantum Numbers

n

Integer Values

Answer 6

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

Question 7

Quantum Numbers

n

Maximum number of electrons in energy level n

Answer 7

2n²

Question 8

Quantum Numbers

n

Relationship between difference in energy levels between adjacent shells and distance from the nucleus

Answer 8

Decreases as distance from the nucleus increases since it is related to the expression 1/n2^{2 -} 1/n1²

Question 9

Quantum Numbers

l

Answer 9

Azimuthal quantum number

Describes the shape of the orbital

Refers to the subshells that occur within each principal energy level

Question 10

Quantum Numbers

l

Integer Values

Answer 10

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

Question 11

Quantum Numbers

l

Maximum number of electrons within a subshell

Answer 11

4l + 2

Question 12

Quantum Numbers

ml

Answer 12

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

Question 13

Quantum Numbers

ml

Integer Values

Answer 13

The possible values are all integers from l to -l including 0

Question 14

Quantum Numbers

ml

Integer Values

L values and Orbitals

1. s subshell
2. p subshell
3. d subshell
4. f subshell

Answer 14

1. l = 0, orbitals: 1 - 2 electrons
2. l = 1, 0, -1, orbitals: 3 - 6 electrons
3. l = 2, 1, 0, -1, -2, orbitals: 5 - 10 electrons
4. l = 3, 2, 1, 0, -1, -2, -3, orbitals: 7 - 14 electrons

Question 15

Quantum Numbers

ms

Integer values

Answer 15

Spin quantum number

+1/2 and -1/2

Question 16

Quantum Numbers

ms

1. Parallel Spins
2. Paired electrons

Answer 16

1. Electrons in different orbitals with the same ms values
2. Electrons with opposite spins in the same orbital

Question 17

Electrons Configurations:

1. Nitrogen
2. Iron

Answer 17

1. Z = 7. Thus electron configuration is

↑↓ ↑↓ ↑↑↑
1s² 2s² 2p³

2. Z = 26

↑↓ ↑↓ ↑↓↑↓↑↓ ↑↓ ↑↓↑↓↑↓ ↑↓ ↑↓↑↑↑↑
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶

Question 18

Z and A

Answer 18

1. Z - atomic number
2. A - mass number

Question 19

Determine the number of protons, neutrons and electrons:

1. Nickel-58
2. Nickel-60 2+ cation

Answer 19

1. A = 58, Z = 28: protons = 28, electrons = 28, neutrons = (58 - 28) = 30
2. A = 60, Z = 28: protons = 28, electrons = (28 - 2) = 26, neutrons = (60 - 28) = 32

Question 20

Atomic mass vs atomic weight

Answer 20

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)

Question 21

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%)

Answer 21

= (0.6 x 40) + (0.25 x 44) + (0.15 x 41)

= 41.15

Question 22

Electrons Configurations:

1. Chromium
2. Copper

Answer 22

1. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵
2. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

Question 23

1. Paramagnetic
2. Diamagnetic

Answer 23

The presence of unpaired or paired electrons affects the chemical and magnetic properties of an atom or molecule.

1. If a material has unpaired electrons, a magnetic field will align the spins of these electrons and weakly attract the atom
2. Materials that have no unpaired electrons and are slightly repelled by a magnetic field are said to be diamagnetic

Question 24

Valence Electrons

1. Group IA
2. Group IIA
3. Groups IIIA - VIIIA
4. Transition elements

Answer 24

1. Outermost s electrons
2. Outermost s electrons
3. Outermost s and p electrons
4. Outermost s, d of next-to-outermost shell, f of shell two below outermost shell

Question 25

Valence Electrons 1. Elemental iron 2. Selenium 3. Sulphur atom of sulphate ion

Answer 25

1. 8 valence electrons: 2 in 4s, 6 in 3d 2. 6 valence electrons: 2 in 4s, 4 in 4p. Selenium's 3d electrons don't form part of its valence shell 3. 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

Question 26

Atom

Answer 26

Smallest representative particle of an element. Composed of protons, neutrons and electrons

Question 27

Proton

Answer 27

Positively charged subatomic particke found in the nucleus

Question 28

Neutron

Answer 28

Electrically neutral subatomic particle found in the nucleus. Has approximately the same mass as a proton

Question 29

Electron

Answer 29

Negatively charged subatomic particle found outside the nucleus. Has a mass of ~1/1836 that of a proton

Question 30

Valence principal energy level

Answer 30

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

Question 31

Electron configuration

Answer 31

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)

Question 32

Principal energy level

Answer 32

Or shell. Each principal energy level within an atom contains one or more sublevels (or subshells)

Question 33

Lewis dot diagram

Answer 33

Shows an element surrounded by a series of dots which represent the valence electrons of the element

Question 34

Atomic Orbitals

Answer 34

Each has no more than two electrons of opposite spin

Question 35

Principal quantum number, n

Answer 35

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

Question 36

Azimuthal quantum number, l

Answer 36

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

Question 37

Magnetic quantum number, ml

Answer 37

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

Question 38

Spin quantum number

Answer 38

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

Question 39

Order of orbital sequencing

Answer 39

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...

Question 40

Maximum numbers of electrons -s sublevel

Answer 40

2

Question 41

Maximum numbers of electrons -p sublevel

Answer 41

6

Question 42

Maximum numbers of electrons -d sublevel

Answer 42

10

Question 43

Maximum numbers of electrons -f sublevel

Answer 43

14

Question 44

Electron Configurations Simplifying Using Noble Gases

Answer 44

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

Question 45

Electron Configurations Hund's Rule

Answer 45

States that for degenerate orbitals, the lowest energy is acheived when the number of electrons with the same spin is maximised