Higher Chemistry Periodicity NEW LEARNING Grouping elements by bonding and structure – focus on Titanium Grouping compounds by bonding and structure. Periodic trends REVISION Elements are the simplest substances and consist of one type of atom. They are arranged in the Periodic table in increasing atomic number.

Starter Task S3 Revision

Lesson 1/2: Trends in Elements Today we will learn to Describe trends in different properties of elements. We will do this by Defining and analysing covalent radius, ionisation energy and electronegativity. We will have succeeded if We can show the pattern of increasing trends on a periodic table.

Trends in Elements To keep oxygen away from the titanium when it was extracted it was important to convert the titanium oxide into another compound that did not contain any oxygen which could then have pure titanium extracted from it. In order to achieve this chemists needed to find another non metal that was more reactive than oxygen and able to displace non-metals from compounds. ACTIVITY 1.10 Halogen Displacement Reactions and the reactivity of the alkali metals. Your teacher might demonstrate displacement reactions of the halogens and/or the reactivity of the alkali metals. DISCUSS After discussion with your teacher and others can you describe the pattern in reactivity for both the alkali metals and halogens as you go down the group: NOTES Briefly describe how the reactivity of alkali metals and then the halogens changes as you go down the group. S3 Revision

Trends in Elements S3 Revision

Trends in Elements S3 Revision

Trends in Elements S3 Revision

Trends in Elements S3 Revision

Trends in Elements S3 Revision

Atomic Size As we go across a period, the nuclear charge and the number of outer electrons increase. As we go down a group, the number of electron shells or energy levels increases but the number of outer electrons stays the same. The covalent radius of an element is half the distance between the centres (nuclei) of 2 bonded atoms. The trend in atomic size (covalent radius) is: Across a period the atomic size decreases as the nuclear charge increases and attracts the outer electrons closer to the nucleus. Down a group the atomic size increases as an extra electron shell is added.

Trends in Elements S3 Revision

Ionisation Energy (Enthalpy) The ionisation energy is the energy absorbed when 1 mole of electrons is removed from a mole of atoms in the gaseous state. The 1st ionisation energy is the energy needed to remove the first mole of electrons and the 2nd ionisation energy is the energy needed to remove the second mole of electrons, etc. e.g. the ionisation energies for magnesium are: 1st Mg(g) Mg+(g) + e- ∆H= 744 kJmol-1 2nd Mg+(g) Mg2+(g) + e- ∆H= 1460 kJmol-1 3rd Mg2+(g) Mg3+(g) + e- ∆H= 7750 kJmol-1 Why the big jump from 2nd to 3rd ionisation energy for Mg?

e.g. between the 2nd and 3rd ionisation energy for magnesium. Examples NB Successive ionisation energies increase as the atom becomes more positive. There is a large jump in ionisation energy when the electron to be removed comes from a new shell, closer to the nucleus. e.g. between the 2nd and 3rd ionisation energy for magnesium. Examples Use your Data Book to calculate the energy required for the following changes: Ca(g) Ca2+(g) + 2e- Al(g) Al3+(g) + 3e- The total energy to remove more than 1 mole of electrons is equal to the sum of each mole added together (as above).

Trends in Ionisation energy Across a period ionisation energies increase. This is because the nuclear charge increases and holds the outer electrons more strongly. Within each period the noble gas has the highest value for the 1st ionisation energy explaining the stability of full electron shells. Down a group ionisation energies decrease. This is because the outer electrons are further away from the nucleus. The screening effect of the inner electron shells reduces the nuclear attraction for the outer electrons, despite the increased (positive) nuclear charge.

Trends in Elements S3 Revision

Electronegativities Electronegativity is a measure of an atom’s attraction for electrons in a bond. e.g. A covalent bond in the element chlorine: Both atoms have the same electronegativity so the electrons are shared equally. e.g. A covalent bond in the compound hydrogen chloride: The bonded atoms have different electronegativities so the chlorine atom has a bigger attraction for the shared electrons than the hydrogen atom. As the electrons are attracted closer to the chlorine it becomes slightly negative (δ-) and the hydrogen atom becomes slightly positive (δ+).

The trend in electronegativity is: Across a period, electronegativity increases. This is because the nuclear charge increases, attracting the electrons more strongly. Down a group, electronegativity decreases. This is because the atoms are bigger, bonding electrons are further away from the nucleus and the screening effect of the inner electron shell decreases the nuclear attraction for electrons.

Exit Task Complete Quick Test 3 in your booklet and we will review as a class. You have 5 minutes! S3 Revision

Answers Quick Test 3 1. B 2. A 3. B 4. D 5. C 6. D S3 Revision