C4: Chemical Patterns

What is a periodic table ? The elements are arranged in order of proton number. There are repeating patterns in the element’s properties. The vertical columns are called groups. The elements in a group have similar properties. The horizontal rows are called periods. The elements to the left of a stepped between aluminium and silicon, germanium and arsenic, and so on are metals, The elements to the right of this stepped line are non-metals,

How was the periodic table created? In the Early 1800s, Dobereiner noticed that there were several groups of 3 elements with similar properties. Newlands arranged the elements in order of relative atomic masses. Every eighth element had similar properties. His pattern only worked for the first 16 elements. Mendeleev showed that there were patterns in the properties of all elements when arranged in relative atomic mass order. He made a sensible pattern by leaving gaps for missing elements. He predicted the missing elements’ properties. Later, scientists discovered these elements.

What do hazard symbols mean SymbolMeaningSafety precautions Wear eye protection and…. Toxic – can cause death, if absorbed by skin, swallowed or breathed in Wear gloves Work in fume cupboard or wear mask over mouth and nose Harmful – like toxic substances, but less dangerous Wash off spills quickly Use in a well –ventilated room Corrosive – attacks surfaces and living tissues like eyes and skin Wear gloves Explosive Avoid situations in which explosion could be initiated. Highly flammable – catches fire easily Keep away form flames, sparks and oxidising chemicals Oxidising – provides oxygen so other chemicals burn more fiercely Keep away from flammable chemicals

Group 1: alkali metals The alkali metals: Have low densities so they float on water Have low melting and boiling points Are shiny when freshly cut Quickly tarnish in damp air because they react with oxygen Going down the group, the reactions get vigorous Alkali metal also react vigorously with chlorine gas to make chlorides – colourless crystalline solids metal + water  Hydrogen + metal hydroxide Metal + chlorine  metal chloride

Group 7: halogens Going down the group, melting point and boiling point increase Diatomic Going down the group, the elements become less reactive Hot iron flows brightly in chlorine gas but it glows less brightly n bromine and hardly at all in iodine. FormulaStateColour Cl 2 GasPale green Br 2 LiquidDeep red liquid with red-brown vapour I2I2 SolidGrey solid with purple vapour

Explaining patterns in the properties of elements ParticleRelative mass Relative charge Proton1+1 Neutron1None Electronnegligible An atom has an nucleus made up of protons or neutrons. Around the nucleus are electrons. All atoms of the same element have the same number of protons. The number of electrons in an atom is the same as the number of protons. Electrons are arranged in shells. Each electron shell fills from left to right across a period. Every group 1 element has one electron in its outer shell. An element’s chemical properties depend on its electron arrangement. So group 1 elements have similar chemical reactions.

Elements have distinctive flame colours When the light from the flame goes through a prism, it makes a line spectrum. Every element has a different spectrum. Compound of elements make different colours. Chemists study these spectra and so discovered new elements such as helium.

What are ions and ionic compounds? If you melt an ionic compound containing metal and non-metal ions, it conducts electricity. Ions carry the current. Ion – atom or group of atoms that has gained or lost electrons. So it has an overall charge. In solid ionic compounds, the ions are arranged in a regular lattice. So solid ionic compounds form crystals. When ionic crystals melt or dissolve in water, the ions are free to move independently. So ionic compounds conduct electricity when liquid or in solution.

Ion calculations Working out the formulae of an ionic compound Charge of each element. The total charge must be 0. Working out the charge on an ion Charge must equal to 0 so by knowing the charge of one ion in a compound can enable you finding out the ion of other element in the compound