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Chemistry (C3) revision…read more

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The periodic table…read more

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The early periodic table
· During 1800's, many elements discovered but scientist didn't know
atom structure, tried to find ways to classify elements based on
properties and atomic weights
· 1863, Newlands proposed
law of octaves, stated similar properties
repeated every 8 element, put 82 elements know into 7 groups
according to atomic weight ­ after calcium properties didn't match
well into groups, so ideas not accepted
· In 1869 Mendeleev produced better table, leaving gaps for unknown
elements so groups of known elements did have similar properties ­
predicted properties of missing elements
· When some of missing elements discovered, predictions confirmed
and more readily accepted his ideas ­ Mendeleev's table became the
basis for modern periodic table…read more

Slide 4

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The modern periodic table
· Scientists found out about protons and electrons at start of 1900s ­ soon after,
developed models if arrangement of electrons in atoms ­ elements arranged in
periodic table order of atomic number (proton numbers) and were lined up in
vertical groups
· Groups of elements have similar chemical properties because their atoms have
same number of electrons in outer shell ­ for main groups, no. of electrons in outer
shells = group number
Reactivity within groups
Within a grows reactivity of elements depends on total no. of electrons, going down a
group are more occupied shells and atoms gets large, as atoms get bigger, electrons
in outer shell are less strongly attracted to nucleus
· When metals reacts they lose electrons so reactivity of metals in group increases
going down group
· When non-metals react they gain electrons, so reactivity of non-metals decreases
going down group…read more

Slide 5

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Group 1 ­ the alkali metals
· Group 1 elements called alkali metals, all metals that react readily with air and water
· Soft solids at room temperature with low melting an boiling points that decrease going down group,
have low densities, so lithium, sodium and potassium float on water
· React with water to produce hydrogen gas and metal hydroxide that is alkali
Sodium + water sodium hydroxide + hydrogen
2Na(s) + 2H2O(l) 2NaOH (aq) + H2(g)
· They all have 1 electron in highest occupied energy level (outer shell) they lose electron in reactions
forming ionic compounds in which their ions have single positive charge, e.g. Na+
· React with halogens (group 7 elements) forming salts that are white/colourless crystals, e.g. sodium +
chloride sodium chloride (2Na(s) + Cl2(L) 2NaCl(s))
· Compounds of alkali metals dissolve in water, forming solutions that are usually colourless
· Going down group 1, reactivity of alkali metals increases
Explanation of reactivity trend in group 1 - Reactivity increases going down group 1 because outer shell
electron is less strongly attracted to nucleus as no. of occupied energy levels (becoming further away
from nucleus) increases and atom gets larger…read more

Slide 6

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The transition metals
· Transition elements found n periodic table between group 2 and 3
· Are all metals and so are sometimes called transition metals
· Except for mercury, they have higher boiling and melting points than
the alkali metals
· React only slowly or not at all with oxygen and water at ordinary
· Most are strong and dense and are useful as building materials, often
as alloys
· Form positive ions with various charges, e.g. Fe2+ and Fe3+
· Compounds of transition metals often brightly coloured
· Many transition metals and their compounds are catalysts for
chemical reactions…read more

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