Chem 111 - Periodicity

Front 1

White light shone through a prism gives a continuous spectrum, what is the contrast with excited atoms?

Back 1

Discrete lines are observed in the emission spectra of excited atoms - every element having specific characteristics within its spectrum.

Front 2

Rudberg found that the wavelengths of the hydrogen spectra follow what relationship?

Back 2

1/λ = R (1/N^2 - 1/n^2)

R = 1.097 x 107 m^-1 (Rydberg constant)

Front 3

In 1900 what did Planck say about the energy of electromagnetic radiation?

Back 3

The energy of electromagnetic radiation is quantised.

E = hv

Front 4

What did Rutherfords model of the atom show?

Back 4

Showed a small positively charged nucleus, containing much of the atom's mass, is surrounded by low-mass electrons.

Front 5

What were the 3 key points in Bohr's model of the Hydrogen atom?

Back 5

1. Electrons orbit the nucleus in distinct circular paths at certain distances.

2. Each orbit (or shell) corresponds to a certain energy level.

3. Electrons can only gain and lose energy by jumping between orbits,thereby absorbing or emitting electromagnetic radiation (∆E = hν).

Front 6

What were the flaws in Bohr's model of the Hydrogen atom?

Back 6

1. According to classical electrodynamics, the orbiting electron (a charged particlemoving in a curve) must radiate energy, lose momentum and eventuallycrash into the nucleus.

2. It could only describe the spectra of one-electron atoms such as the hydrogen atom,but it fails to explain the more complex spectra of many-electron atoms.

Front 7

What did De Broglie argue?

Back 7

De Broglie (1924) argued that very tiny particles such as electrons show bothparticle and wave-like behaviour. This is called wave-particle duality.

Front 8

What principle of Heisenberg's led to a better understanding?

Back 8

Heisenberg concluded that due to the wave-particle dualityit is impossible to know the exact positionx andmomentump of a particle simultaneously.This is called the uncertainty principle.

Therefore only probabilities can be used in this scale.

Front 9

What is the probability of finding an electron proportional to?

Back 9

The probability of finding an electronat a given location is proportionalto the square of the wavefunction ψ2.

ψ2 is also called the probability densityof the electron.

Front 10

What is quantum number "n"?

Back 10

n - principle quantum number

Front 11

What is quantum number "l"?

Back 11

l - angular momentum quantum number

Describes the shape of an orbital.

Front 12

What is quantum number "ml"?

Back 12

ml - magnetic quantum number

Gives the direction of the orbitals.

Front 13

The sum of radial and angular nodes?

Back 13

The sum of radial and angular nodes is n-1

Front 14

The number of angular nodes?

Back 14

The number of angular nodes is l

Front 15

The number of radial nodes?

Back 15

The number of radial nodes is n-1-l

Front 16

What rules must be obeyed when building up energy levels?

Back 16

Orbitals are filled in order of energy, the lowest energy orbital availableis being filled first.

Pauli's exclusion principle.

Hund's rule.

Front 17

What is Pauli's exclusion principle?

Back 17

No two electrons in the same atom may have the sameset of quantum numbers n, l, ml and ms, (where ms is the spin quantum numberwhich can either be +½ or -½).

It follows that each orbital can accommodate a maximum of two electronsboth having different spins (+½ and -½).

Front 18

What is Hund's rule?

Back 18

In a set of degenerate orbitals (orbitals of same energy), orbitals willbe occupied by single electrons of parallel spins before being filled with pairs.

This is due to the fact pairing costs spin energy.

Front 19

Orbitals with higher quantum number "l" are?

Back 19

Orbitals with a higher quantum number l are less effective in penetratingand shielding.

Front 20

Define Ionisation Energy.

Back 20

The ionisation energy Ei is the minimum energy needed to remove an electron from anatom in the gas phase.

Front 21

Define First Ionisation Energy.

Back 21

The first ionisation energy is the energy requiredto remove the least tightly bound electronfrom the neutral atom.

Front 22

Is ionisation an endothermic or exothermic process?

Back 22

Ionisation of a neutral atom isan endothermic process (it requires energy).

Therefore ionisation energies have positive values.

Front 23

Define electron gain energy?

Back 23

Electron gain energy is the energy change encountered when an atom is gaining an electron.

Front 24

Define electron affinity?

Back 24

Electron affinity is the reverse process of the energy change when an atom gains an electron, in the atoms gaseous state.

Reverse process of electron gain.

Front 25

Define the atomic radius.

Back 25

The atomic radius r is defined ashalf the internuclear distanceof two neighbouring atoms ofthe same element in a metallicsolid or in a molecule.

Front 26

Define electronegativity.

Back 26

The electronegativity χis defined as the power of anatom in a molecule to attractelectron density to itself.