Atomic Structure

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Structure of the atom

Protons, neutrons and electrons - neutrons are the heaviest (only by a little)

Relative atomic mass: The mean weighted mass of one mole of an element compared to the mass of one twelfth of a mole of carbon 12

Isotopes

Atoms of the same element with the same number of protons but different number of electrons

Relative atomic mass = sum of (abundance x mass) / total abundance

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Mass spectrometry

Is the way that atomic mass is determined there are 5 steps which can be remembered as VIADD

Step 1 - Vaporisation

The sample is injected and vaporised in a vacuum

Step 2 - Ionisation

This can be done in one of two ways either electron impact or electron spray and is they way of making a positive ions.

Electron impact is where high energy electrons are fired at the sample from an 'electron gun' which is a hot wire filament with a current running through it that emits electron. This knocks off an electron from the particle forming a 1+ ion. This used for elements + substances with a low formula mass.

Electron spray is where the sample is dissolved in a volatile solvent and injected through a fine hypodermic needle to give a fine mist (aerosol). The needle is attached to the positive terminal of a high-voltage power supply - the particles are ionised by gaining a proton.

Step 3 - Acceleration

The now positively charged electrons are attracted to the negative plate and are accelerated into the flight tube. All the particles have the same kinetic energy however the velocity depends on the mass of the substance.

Step 4 - Ion drift

The positive ions go through a hole in the negatively charged plate and drift down the flight tube at different speeds - the time it taken be used to work out the mass of the particle

Step 5 - Detection

The positive ions hit a negatively charged electric plate. When they hit the plate, the positive ions are discharged by gaining electrons from the plate. This generated a movement of electrons and hence an electric current that is measured. The size of the current gives an abundance of the ions hitting the plate.

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Electron Configuration

Each energy level is divided into sub levels named s, p, d and f shells

If each energy level is given a number n, the max number of e- in a shell s 2n^2

Orbitals have a 3 dimensional volume where an electron probably exists - an orbital can only contain 2 electrons

S orbitals are a sphere and there is 1 in each energy level

P orbitals are lobal (figure 8) and there are up to 3 in each energy level (not in first). Double bonds rely on P orbitals

D orbitals are weird shapes and there are up to 5 in each level starting with the 3rd

They fill up in order of energy level (lowest first)

The Rules are:

Lower atomic orbits fills first

Sub levels of the same energy fill singularly before electrons pair with opposite spins (fill on their own first) - all Ps

Orbitals contain a max of 2 electrons

4s orbitals are lower energy than 3d

Transition metals - half filled or fully filled orbitals are more stable than s orbitals, when ions form 4s electrons are lost first

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First Ionisation energies

- Ionisation energy is the energy required to remove an electron - it os how we know about the position of electron shells

F.I.E : energy required to remove a mol of electrons from a mol of atoms in the gaseous state

Successive energies become greater because you are removing -ve electron from a +ve ion - if there is an order of magnitude jump in ionisation energy then you are removing an electron from a new inner shell

Trend in ionisation energy - see periodicity

Period 3 exceptions:

Mg to Al because Mg's outer electron is in a s-orbital but Al's in a p-orbital as Al's outer e- in is a higher energy level then it is easier to remove and the FIE is therefore lower.

P to S as the outer electron in P is unpaired but in S it is paired. In S the outer e- is facing some repulsion from the other e- in it's orbital but in P it isn't. As there is less attraction it is easier to remove and the FIE is lower in S