Electronic Structure In Shells

L.O. Define what a shell is.

L.O. Understand how they’re filled.

L.O. Explain and Describe the different types of bonding.

Neil’s idea of Levels became outdated and out-fashioned because it was too simple. This is when the idea of Shells came in.

Shells are groups of orbitals.

This is a more complex concept because the levels idea only includes distance measurements – but no shape or location values …etc

N=1 is the first shell. Contains 2 electrons.

N=2 is the second shell. Contains 8 electrons.

N=3 is the third shell. Contains 18 electrons.

Etc

You can only get S orbitals in n=1.

You can only get S and/or P orbitals in n=2.

You can only get S and/or P and/or D orbitals in n=3.

Etc

	Atomic Number	N=1	N=2	N=3	N=4
Hydrogen	1	1
Helium	2	2
Lithium	3	2	1
Beryllium	4	2	2
Boron	5	2	3
Carbon	6	2	4
Nitrogen	7	2	5
Oxygen	8	2	6
Fluorine	9	2	7
Neon	10	2	8
Sodium	11	2	8	1
Magnesium	12	2	8	2
Aluminium	13	2	8	3
Silicon	14	2	8	4
Phosphorus	15	2	8	5
Sulfur	16	2	8	6
Chlorine	17	2	8	7
Argon	18	2	8	8
Potassium	19	2	8	8	1
Calcium	20	2	8	8	2
Scandium	21	2	8	9	2
Titanium	22	2	8	10	2
Vanadium	23	2	8	11	2
Chromium	24	2	8	12	1
Manganese	25	2	8	13	2
Iron	26	2	8	14	2
Cobalt	27	2	8	15	2
Nickel	28	2	8	16	2
Copper	29	2	8	18	1
Zinc	30	2	8	18	2
Gallium	31	2	8	18	3
Germanium	32	2	8	18	4
Arsenic	33	2	8	18	5
Selenium	34	2	8	18	6
Bromine	35	2	8	18	7
Krypton	36	2	8	18	8

n.b. The Group Number of an element is equal to the amount of electrons in its outermost shell.

Ionic Bonding	Covalent Bonding	Metallic Bonding
A metal, and a nonmetal	2 non metals	2 metals
Gain or loss of electrons	Sharing electrons	Sharing electrons

The objective of any bonding process is for atoms to become stable via filling their outermost shells.

Polarity & Electronegativity

The electron pairs shared between two atoms are not necessarily shared equally.

Bond polarity is a useful concept for describing the sharing of electrons between atoms.

A non-polar covalent bond is one in which the electrons are shared equally between two atoms.

A polar covalent bond is one in which one atom has a greater attraction for the electrons than the other atom. If this relative attraction is great enough, then the bond is an ionic bond.

Electronegativity of an atom is its ability to attract electrons to itself.

Dative bonding is when one element in a compound donates both electrons required for the bond to take place.

An example of this is Nitrous Oxide.

Spectroscopy continued.

·         The Absorption Spectra looks at the frequencies absorbed by an element when light is passed through it

Light  à Gas à Less light

·         The Emission Spectra looks at the light given off when the element is exited

Excited element (heated up) à light is emitted. (Bohr’s theory)

·         Wave theory and particle theory are linked by Planck’s constant.

Bohr’s theory

Bohr stated that electrons start in their normal shell (Ground level or level 1: closest to the nucleus) but the atom still has outer shells (level 2, 3 …etc)

When the electron gains energy, the electron moves + shell, depending on the amount of energy (Which is known as a quantum: the energy required for an electron to jump up to the next level)

When the electron is in a higher level, it’s known to be in an ‘excited state’. However, the electron can’t stay in the excited state after the energy is given off (so it moves back to ground level)

Bohr:  As the electron jumps up a quantum, it absorbs light, which is why we get an absorption spectra. As it jumps back down, it emits the light it absorbed.

Bohr:  As you go towards outer shells, the layers get closer get closer to each another. Which is significant as it justifies why the frequency given off is different as the quantum gets smaller.

The energy of the photon is equal to the quantum. Knowing that, we can calculate frequency.

Both the photon value and the quantum are variables according to the level which the electron is at.

Petrol Components

Petrol is a mixture of:

Alkanes (Aliphatic/saturated) which are often in the three forms of

Straight chains (Typical hydrocarbons such as Ethane)

 Branched chains (Hydrocarbons with extra bonds such as 2-Methyl butane)

 Cyclic chains (Hydrocarbons in a circular structure such as Cyclohexane).

A few Alkenes such as the aromatic Benzene C₆H₆

(Aromatic Hydrocarbons: Hydrocarbons characterized by general alternating double and single bonds between carbons)

Alcohol

Which is increasing in amounts as a component in fuel over the years.

e.g. Ethanol and Ethers

(Ethers are 2 alkenes connected by an Oxygen [such as Ethoxyethane])

Petrol is/needs to be a blend of volatilities, and to burn well, i.e. not produce a lot of carbon monoxide.

Alcohols and ethers are known as oxygenates as they contain Oxygen.

Ethanol can be produced from fermentation, so it’s a biofuel.

Cons: Ethanol and ethers produce less energy per unit. (Low energy density) and that Ethanol is hydroscopic (Absorbs water) which may cause rust in vital components i.e. engine.

Spectroscopy

Recap on related topics:

-    The theory of star formation is a model developed by observing different stars and realising that each is at a different stage.

-          In outer ‘space’ there’s roughly 1 atom present per cm³

-          Dense gas Clouds take place between stars and consists of plasma, nuclei, electrons, ions and dust of other stars that combusted due to Super Novas.

-          In Dense gas clouds, particles have low kinetic energy, which promotes gravitational forces to hold the molecules together. This eventually results in parts of the clouds compressing.

-          Nuclear fusion is a nuclear reaction – it is when nuclei join.

Overview:

Spectroscopy is the study of light and matter.

We use two models to describe light.

1-      The Particle Model

This was deviced by Alvert Einstein. He suggested that light is a stream of photon packages, and that the energy of the photons is relative to the position of the light in the electromagnetic spectrum.

Max Planck suggested that E = h v

Where E is the energy of a photon.

V is the frequency of the light.

h is the “Planck constant” which is equal to 6.63 x 10^-34

2-      The Wave Model

The wave model centres around the idea that light, as a part of the electromagnetic spectrum has a wave with specific characteristics (Wave length and frequency).

n.b. Speed of light (Symbol c) is equal to 3.00 x 10⁸ ms^-1

        Wave length is symbol λ

        Freqncy is symbol v

c =  λ v

Hess's Law!

Hess’s Law

“The overall enthalpy change of a reaction is independent of the route taken.”

Example question:

Given that Δ H ^θ _combustion of water is -286 KJ mol^-1

Given that Δ H ^θ _combustion of Carbon dioxide is -394 KJ mol^-1

Given that Δ H ^θ _combustion of Methanol is -726 KJ mol^-1

Calculate the Δ H ^θ _formation of Methanol.

Step 1 – Balance the equation.

C + H₂ >> C₈H₁₈

C + 2 H₂ >> C₈H₁₈

Step 2 – Make the route diagram and label the Δ H’s

Step 3 – realise the route.

In this case, we want Δ H4+ Δ H3 which is equal to Δ H1 + Δ H2

This is because, regardless of what route we take, we end up getting the same product, and therefore the enthalpy change will be the same.

Step 4 – Substitute the values

Δ H1 + Δ H2 = Δ H3 + Δ H4

-394 + (2x-286) = Δ H1 + -726

-966 = Δ H3 – 726

- make the wanted delta H the subject of the formulae, and add the unit. -

Δ H3 = -966 + 726

Δ H3 = -240 Kj Mol ^-1

Thermochemical Definitions

Standard Bond Enthalpy is the energy needed to break a gaseous covalent bond into gaseous component atoms in standard temperature and pressure.

e.g. H-H >> 2H

Standard Enthalpy of Formation is the total enthalpy change when 1 mole of product is formed from its component elements in their standard states.

Standard Enthalpy of Combustion is the total enthalpy change when 1 mole of reactant burns in excess Oxygen.

Standard Enthalpy of Reaction is the total enthalpy change when a specific reaction goes to completion.

* Standard Temperature is 298 Kelvin (25 C)

* Standard Pressure is 1 atmosphere

* Standard State is how you'd find the element at Standard temperature and pressure.

Group S elements

… are group 1 and group 2 on the periodic table.

A level students should identify those as Alkali metals and alkali earth metals, despite their lack of “Metal-like” properties.

Group S are generally reactive, and are relatively soft for metals.

Group 1 elements are less dense than water.

Francium and Radium are radioactive, and Cesium will react very violently with water. (Explosion)

Group S compounds are more useful than the elements.

They’re naturally found as ores.

Mostly, all S elements are reactive with water making Alkali solutions.

e.g. Magnesium + Water >> Magnesium Hydroxide + Hydrogen

The lower down the table, the more reactive the elements, for example Barium is more reactive than Magnesium.

All reactions in group 2 are more violent than group 1.

Group 2 is soluble, but less soluble than Group 1.

Group 2 makes stronger alkali solutions  (11-14 on the pH scale)

The lower down the table, the stronger the alkality. This is useful for neutralising acidic soil, whilst the salt bi product gets trapped in clay.

Thermal Stability: Unreactive elements give reactive compounds. And the further down the S group, the more stable the element.

Hydroxides are more solube as we go down the S group.

+1 ions[Hydroxides] (Chlorides, Bromides, Iodides, Nitrates)

Carbonates are less solube as we go down the S group.

-2 ions [Carbonates] (Sulphates, Oxides)