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Criado por Samuel Marsh
mais de 11 anos atrás
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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
C3.1
C3.2
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