Atomic Structure Atoms are very small ~ metres All atoms are made up of three sub-atomic particles: protons, neutrons and electrons

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1 IB Chemistry (unit ) ATOMIC THEORY Atomic Structure - Recap Questions Define the following words: Atom Element Molecule Compound Atomic Structure Atoms are very small ~ - metres All atoms are made up of three sub-atomic particles: protons, neutrons and electrons Atomic Structure The actual values of the masses and charges of the sub-atomic particles are shown below: Atomic Structure - Definitions Atomic number (Z) is the number of protons in the nucleus of an atom. It is also known as the proton number. N.B. No. of protons always equals the no. of electrons in any neutral atom of an element. Mass number (A) is the sum of the number of protons and the number of neutrons in the nucleus of an atom. Atomic Structure - Example Atomic Structure - Questions What are the three sub atomic particles that make up the atom? Draw a representation of the atom and labelling the sub-atomic particles. Draw a table to show the relative masses and charges of the sub-atomic particles. State the atomic number, mass number and number of neutrons of: a) carbon, b) oxygen and c) selenium. Which neutral element contains electrons and neutrons? Atomic Structure - Questions. Copy and complete the following table:

2 Summary Slide All atomic masses are relative to the mass of carbon-. Eg one hydrogen atom weighs / the mass of a carbon- atom. Isotopes Isotopes are atoms of the same element with the same atomic number, but different mass numbers, i.e. they have different numbers of neutrons. Isotopes Isotopes of an element have the same chemical properties because they have the same number of electrons. When a chemical reaction takes place, it is the electrons that are involved in the reactions. However isotopes of an element have the slightly different physical properties because they have different numbers of neutrons, hence different masses. The isotopes of an element with fewer neutrons will have: Lower masses faster rate of diffusion Lower densities lower melting and boiling points Isotopes - Questions Explain what isotopes using hydrogen as an example. One isotope of the element chlorine, contains neutrons. Which other element also contains neutrons? State the number of protons, electrons and neutrons in: a) one atom of carbon- b) one atom of carbon- c) one atom of uranium- d) one atom of uranium- Mass Spectrometer The mass spectrometer is an instrument used: To measure the relative masses of isotopes To find the relative abundance of the isotopes in a sample of an element Mass Spectrometer Stages Once the sample of an element has been placed in the mass spectrometer, it undergoes five stages. Vaporisation the sample has to be in gaseous form. If the sample is a solid or liquid, a heater is used to vaporise some of the sample.

3 Mass Spectrometer Stages Ionisation sample is bombarded by a stream of high-energy electrons from an electron gun, which knock an electron from an atom. This produces a positive ion: Mass Spectrometer Stages Deflection Mass Spectrometer If all the ions are travelling at the same velocity and carry the same charge, the amount of deflection in a given magnetic field depends upon the mass of the ion. For a given magnetic field, only ions with a particular relative mass (m) to charge (z) ration the m/z value are deflected sufficiently to reach the detector. Mass Spectrometer Detection ions that reach the detector cause electrons to be released in an ion-current detector The number of electrons released, hence the current produced is proportional to the number of ions striking the detector. The detector is linked to an amplifier and then to a recorder: this converts the current into a peak which is shown in the mass spectrum. Atomic Structure Mass Spec Name the five stages which the sample undergoes in the mass spectrometer and make brief notes of what you remember under each stage. Complete Exercise, and in the handbook. Any incomplete work to be completed and handed in for next session. A mass spec chart for a sample of neon shows that it contains:.% Ne.% Ne.% Ne Calculate the relative atomic mass of neon You must show all your working!.% Ne.% Ne.% Ne Calculate the relative atomic mass of lead You must show all your working!

4 .% Pb.% Pb.% Pb.% Pb Electrons go in shells or energy levels. The energy levels are called principle energy levels, to. The energy levels contain sub-levels. Each type of sub-level can hold a different maximum number of electron. The energy of the sub-levels increases from s to p to d to f. The electrons fill up the lower energy sub-levels first. Let s take a look at the Periodic Table to see how this fits in. So how do you write it? The electronic structure follows a pattern the order of filling the sub-levels is s, s, p, s, p After this there is a break in the pattern, as that the s fills before d. Taking a look at the table below can you work out why this is? The order in this the energy levels are filled is called the Aufbau Principle. Example (Sodium,, ) There are two exceptions to the Aufbau principle. The electronic structures of chromium and copper do not follow the pattern they are anomalous. Chromium s, s, p, s, p, d, s Copper s, s, p, s. p, d, s of ions When an atom loses or gains electrons to form an ion, the electronic structure changes: Positive ions: formed by the loss of e - of transition metals With the transition metals it is the s electrons that are lost first when they form ions: Titanium (Ti) - loss of e - - Questions Give the full electronic structure of the following positve ions: a) Mg + b) Ca + c) Al + Give the full electronic structure of the negative ions: a) Cl - b) Br - c) P - - Questions Copy and complete the following table: The energy sub levels are made up of orbitals, each which can hold a maximum of electrons. Different sub-levels have different number of orbitals:

5 The orbitals in different sub-levels have different shapes: Within a sub-level, the electrons occupy orbitals as unpaired electrons rather than paired electrons. (This is known as Hund s Rule). We use boxes to represent orbitals: The arrows represent the electrons in the orbitals. The direction of arrows indiactes the spin of the electron. Paired electrons will have opposite spin, as this reduces the mutual repulsion between the paired electrons. Ionisation Energy Ionisation of an atom involves the loss of an electron to form a positive ion. The first ionisation energy is defined as the energy required to remove one mole of electrons from one mole of atoms of a gaseous element. The first ionisation energy of an atom can be represented by the following general equation: X (g) X + + e - H +ve Since all ionisations requires energy, they are endothermic processes and have a positive enthalpy change ( H) value. Ionisation Energy The value of the first ionisation energy depends upon two main factors: The size of the nuclear charge The energy of the electron that has been removed (this depends upon its distance from the nucleus) Ionisation Energy As the size of the nuclear charge increases the force of the attraction between the negatively charged electrons and the positively charged nucleus increases. Ionisation energy As the energy of the electron increases, the electron is farther away from the nucleus. As a result the force of attraction between the nucleus and the electron decreases.

6 Ionisation energy - Questions Write an equation to represent the first ionisation of: a) aluminium b) lithium c) sodium Trends across a Period Going across a period, the size of the st ionisation energy shows a general increase. This is because the electron comes from the same energy level, but the size of the nuclear charge increases. Trends across a Period ( exceptions) The first ionisation of Al is less than that of Mg, despite the increase in the nuclear charge. The reason for this is that the outer electron removed from Al is in a higher sub-level: the electron removed from Al is a p electron, whereas that removed from Mg is a s. Trends across a Period ( exceptions) The first ionisation energy of S is less than that of P, despite the increase in the nuclear charge. In both cases the electron removed is from the p sub-level. However the p electron removed from S is a paired electron, whereas the p electron removed from P is an unpaired electron. When the electrons are paired the extra mutual repulsion results in less energy being required to remove an electron, hence a reduction in the ionisation energy. Trends across a Period - Questions There is a break in this general trend going across a Period. Look at the table below and point out where the break in the the trend is and try to give an explanation. Trends across a Period - Questions Now take a look at the graph below: Trends down a Group Ionisation energy - Questions Explain why sodium has a higher first ionisation energy than potassium. Explain why the first ionisation energy of boron is less than that of beryllium. Why does helium have the highest first ionisation energy of all the elements? Complete Tasks Successive Ionisation energy Definition: nd i.e. The energy per mole for the process X + (g) X + (g) +e - And so on for further successive ionisation energies Successive Ionisation energy Successive i.e s increases because electrons are being removed from increasingly positive ions. Therefore, nuclear attraction is greater. Large jumps seen when electron is removed form a new sublevel closer to the nucleus Successive Ionisation energy Electron Affinity Electron Affinity

THE STRUCTURE OF ATOMS. ATOMS Atoms consist of a number of fundamental particles, the most important ones are...

THE STRUCTURE OF ATOMS. ATOMS Atoms consist of a number of fundamental particles, the most important ones are... Atomic Structure THE STRUCTURE OF ATOMS ATOMS Atoms consist of a number of fundamental particles, the most important ones are... Mass / kg Charge / C Relative mass Relative Charge PROTON NEUTRON ELECTRON