Chemistry C3 revision

The 19th Century: elements had not been discovered scientists did not know the structure of atoms classified the elements based on atomic weights and structure

The early periodic table

Newlands (1963):Proposed the law of octaves: similar properties are repeated every 8th element put all known elements into 7 groups

Mendeleev (1869):Improved table of elements: left gaps for undiscovered elements groups of known elements did have similar properties predicted properties of unknown elements were readily excepted once more elements were discovered

The modern periodic table

The 20th century protons and electrons were discovered developed models of the arrangement of electrons in the atom were arranged in the periodic table in order of their atomic numbers and lined up in vertical groups

Groups: have similar chemical properties same amount of electrons in their outer shell the number of electrons on the atoms outer shell is the same as the group number

Reactivity within groups: reactivity of elements depend on the total of electronsAtom gets larger as you go down a group as they get larger, the electrons in outer shell are less stronly attracted to nucleus     metals react --> lose electron          reactivity of metals in a group increases going down the group     non-metals react --> gain electron          reactivity of non-metals in a group decreases going down the group

Group 1 - the alkali metals

Physical properties: react readily with water and air soft solids at room temperature low melting and boiling points decrease going down group low densities

React with water to produce hydrogen gas and a metal hydroxide that is an alkali: sodium +   water  --> sodium hydroxide + hydrogen  2Na(s) + 2H2O(l) -->     2NaOH (aq)     +    H2(g)

Chemical properties have one electron on their outer shell they loose their electron on its outer shell in reactions to form ionic compounds in which their ions have a single positive charge

React with halogens (group 7) to form salts and crystals sodium + chlorine --> sodium chloride  2Na(s) +   Cl2(g)  -->      2NaCl(s)

Explanation of reactivity trend in group 1: Reactivity increases going down group 1 outer electron is less strongly attracted to the nucleus as the number of occupied energy levels increases and the atoms get larger

The transition metals

Physical properties: have higher melting and boiling points than alkali metals (excluding mercury) they are malleable and ductile good conductors of heat and electricity react slowly/not at all with oxygen and water at ordinary temperatures most are strong and dense usefull building materials (often as alloys)

Chemical properties: they form posotive ions with carious charges e.g. Fe     and  Fe compounds of transition metals are often brightly coloured many transition metals and their compounds are catatlysts for chemical reactions

2+                 3+

Group 7 - the halogens

Physical properties: non-metals small molecules made up of pairs of atoms low melting and boiling points that increase going down the group

Colours at room temperature: flourine = pale yellow gas chlorine = green gas bromine = red-brown liquid iodine = grey solid iodine = vaporises to a violet gas

Chemical properties: have seven electrons in their outer shell form ionic compound with metals in which the halide ions have a charge of -1 bond covalently with non-metals, forming molecules more reactive halogen able to displace a less reactive halogen nin an aqueous solution of halide compounds

Explanation of reactivity trend for group 7: reactivity decreases going down the group attraction of outer electrons to the nucleus decreases as the number of occupied energy levels (shells) increase

Hard water

Properties: Uses more soap to produce lather

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