Chapter 2
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who invented the periodic table?
Dmitri Mendeleev
how many elements are there?
about 100 (118)
groups (vertical columns) indicate what?
the number of electrons in the outer shell of an element
what do the periods indicate?
the number of shells an atom has
why do elements of the same group have similar properties?
they have the same number of electrons in their outer shell
how many electrons do group 2 elements have in their outer shell?
2
group 1 elements are…
alkali metals
group 7 elements are…
halogens
group 0 elements are…
noble gases
what do the properties of elements depend on?
the number of electrons they have in their outer shell
how are electrons arranged in the shells?
they always fill the first shell first
how to figure out the electronic configuration of an atom?
• the atomic number indicates the number of protons and therefore electrons • the period indicates the number of shells of an atom • e.g nitrogen has 7 electrons and is found in period 2 so its electronic configuration is 2,5
find the electronic configuration of sodium using groups and periods
• sodium is in period 3, so it has 3 shells occupied • the first 2 shells must be full (2,8) • sodium is in group 1 so it has 1 electron in its outer shell • 2,8,1
what can elements be classified as?
metals and non-metals
metals are found on..
the left hand side of the periodic table
non metals are found on the..
right hand side of the periodic table
where are metals and non-metals separated?
they are separated by a zig-zag going from Boron to Astatine
properties of metals
• metals conduct electricity because they allow charge to pass through them easily • metal oxides are basic (they will neutralise acids) • metal oxides which dissolve will form solutions with a pH of more than 7
non-metals
• poor conductors of electricity • non-metal oxides are acidic (they will neutralise bases) • they dissolve in water to form solutions with a pH of less than 7
group 0
• noble gases are all inert, colourless gases • inert - don’t react with much at all
why are noble gases inert?
it takes a lot of energy to add or remove electrons from a noble gas atom
ionic bonding
• atoms lose or gain electrons and become ions • the oppositely charged ions are strongly attracted to one another by electrostatic attractions
simple ions form when…
atoms lose or gain electrons
negative ion
anion - gain electrons