Periodicity

• How are elements in the periodic table arranged?

  By increasing atomic number
• Elements in the same group have...?

  Similar chemical properties and the same number of electrons in their outer shell
• Periods are in...? Elements in the same period have...?

  Rows

  The same number of electron shells
• Define first ionisation energy

  The energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions

  X --> X+ + e-

  
• Atomic radius

  The greater the distance between the nucleus and outer electrons, the less the nuclear attraction.

  
• What are the factors affecting ionisation energy?

  - Nuclear charge

  - Atomic radius

  - Electron shielding

  
• Nuclear charge

  The more protons there are in the nucleus of an atom, the greater the attraction between nucleus and outer electrons

  
• Shielding

  Inner electron shells repel the outer shell electrons. This reduces the attraction between the nucleus and outer shell electrons

  
• General Pattern across a period

  There is a general increase in first ionisation energy across a period (exception: Be --> B and N --> O) . But then there is a sharp decrease between the end of one period and the start of another

  
• What is the trend of ionisation energy down a group?

  First ionisation energy decreases down a group.

  Atomic radius: Atomic radius increases down a group. This means the outer electron shell is further from the nucleus.

  Nuclear charge: Nuclear charge increases but it is outweighed by the increased shielding

  Shielding: Shielding increases meaning that there are more inner shells that repulse the outer shell electrons.

  Nuclear attraction decreases between the outer electron shell and nucleus - therefore the first ionisation energy decreases

  
• What is the trend of first ionisation energy across Period 2 and 3?

  Nuclear charge: Nuclear charge increases as there are more protons in the nucleus (increasing nuclear attraction)

  Shielding: It is the increase across the same shell; so shielding is similar

  Atomic radius: Atomic radius decreases across a period

  Nuclear attraction increases between the outer electron shell and nucleus - therefore more energy is required to remove the outer electron and first ionisation energy increases.

  
• Where are the 2 falls in ionisation energies?

  - Beryllium --> Boron

  - Nitrogen ---> Oxygen

  
• Beryllium to Boron

  - The 2p sub-shell in boron has higher energy than the 2s sub-shell in beryllium.

  - In boron the 2p electron is easier to remove than one of the 2s electron in beryllium

  - Therefore, the first ionisation energy of boron is less than the first ionisation energy of beryllium

  
• Nitrogen to Oxygen

  In nitrogen, the electrons in the 2p orbital are paired individually.

  In oxygen, the paired electrons in one of the 2p orbitals repel one another, making it easier to remove an electron from an oxygen atom than a nitrogen atom.

  Therefore, the ionisation energy of oxygen is less than the first ionisation energy of nitrogen

  
• Define metallic bonding

  The strong electrostatic attraction between positive ions and delocalised electrons

  
• Metallic Bonding

  The positive ions in a solid metal structure are fixed in position (maintains structure and shape). Whereas, the delocalised electrons are mobile and move throughout the structure
• What is a giant metallic lattice?

  A 3D structure of positive ions and delocalised electrons, bonded together by strong metallic bonds
• Properties of Metals

  - High electrical conductivity

  - High melting and boiling points

  - Do not dissolve
• Explanation of properties of metals

  - Can conduct electricity: Metals conduct electricity in solid and liquid state. The sea of delocalised electrons are mobile and carry charge throughout the structure.

  - High melting and boiling point: They have strong electrostatic attractions and so high temperatures are necessary to provide a large amount of energy to overcome the strong electrostatic attraction between the positive ions and delocalised electrons

  - Insoluble: The metallic bond is too strong to break and so metals are insoluble (more likely to lead to a reaction than dissolve)

  
• What is a giant covalent lattice?

  3D structure of billions of atoms held together by strong covalent bonds

  Example: Boron, carbon and silicon
• Properties of Giant covalent structures

  - High melting and boiling points: This is because they have strong covalent bonds. Therefore provide a large quantity of energy needed to break the strong covalent bonds/*-

  - Insoluble: in almost all solvents. The covalent bonds holding the atom in the lattice are far too strong to be broken

  - Do not conduct electricity (exceptions graphene + graphite): Diamond --> Each carbon is bonded 4 times in a tetrahedral shape. Cannot conduct electricity as all it does not have any delocalised electrons (all 4 outer electrons are used)

  Graphite --> Layers slide easily as there are weak forces between the layers. Both graphene and graphite can conduct electricity as the carbon is bonded 3 times, the 4th is delocalised

  Graphene --> Single layer of graphite. As it is only one atom thick, it is lightweight and transparent. Both graphene and graphite are excellent conductors of electricity as they have free delocalised electron that can carry charge

  USES: Aircraft shells, smart phone screens

  
• Variation in melting points across Periods 2 and 3

  Across Periods 2 and 3, the melting point increases. However, there is a sharp decrease in melting point between group 4 and 5. The sharp decrease marks the change from a giant to simple molecular structure.

  When melting, giant structures have strong forces to overcome and so have high melting points, whereas simple molecular structures have weak forces to overcome; hence they have low melting points

  
• Summary of Bonding

  
• Group 2 elements form...?

  2+ ions
• All group 2 elements have an electron configuration that ends in...?

  s2
• Why are group 2 elements called reducing agents?

  It reduces another species. The group 2 element will become oxidised as another species gains 2 electrons and becomes reduced

  
• Redox reactions with oxygen

  Group 2 elements all react with oxygen to form a metal oxide.

  
• Redox reactions with water

  Group 2 elements react with water to form an alkaline hydroxide and hydrogen gas. The reactions become more vigorous down the group (e.g. magnesium reacts very slowly) - reactivity increases

  
• Redox reactions with dilute acids

  metal + acid --> salt + hydrogen

  Reactivity increases down the group
• What is the trend in ionisation energy and reactivity of Group 2 elements?

  As you go down Group 2, ionisation energy decreases and reactivity increases.

  Ionisation energy decreases because there is less attraction between the outer electrons and the nucleus (as a result of increasing atomic radius + shielding)

  Reactivity increases from the energy input of the first and second ionisation energies

  
• Reaction of Group 2 compounds

  Metal oxides of group 2 react with water, releasing hydroxide ions and forming alkaline solutions.

  
• Trend in alkalinity

  The solubility of the Group 2 hydroxides increases down the group, so the solution contains more OH- ions and are more alkaline.

  For example, Mg(OH)2 is only slightly soluble in water. The solution has a low concentration of OH- ions and a pH ~ 10

  Whereas, Ba(OH)2 is more soluble in water. The solution has a higher concentration of OH- ions and a pH ~ 13.

  
• Uses of Group 2 compounds as bases

  - Agriculture: Calcium hydroxide is used on fields by farmers to increase the pH of acidic soils. The calcium hydroxide neutralises the acid in the soil, forming neutral water

  - Medicine/treating indigestion: Group 2 bases are often used as antacids for treating acid indigestion

  
• All halogens exist as what at room temperature and pressure...?

  Diatomic molecules
• What is the trend in boiling points as you go down the halogens?

  More electrons

  Stronger London Forces

  More energy required to break the London forces

  Boiling point increases
• The outer shells of halogens have the configuration of...?

  s2p5
• Why are halogens oxidising agents?

  It has oxidised another species

  Another species loses electrons to halogen atoms

  
• Colour of halogens in water and cyclohexane

  Chlorine --> Pale Green

  Bromine --> Orange

  Iodine --> Brown
• What does the displacement reaction between halogens and halides show about reactivity?

  Reactivity decreases
• Chlorine (Cl2) reaction with other halogens

  Chloride (Cl-) --> Cannot react (colourless)

  Bromide (Br-) --> Yellow colour (aq)/ Orange colour (organic)

  Iodide (I-) --> Brown colour (aq) /Violet colour (organic)