chemistry - key concepts in chemistry: the periodic table (1.13 - 1.20)

1.13 how did Mendeleev arrange elements in periodic table?

in order of increasing RAMs

sometimes swapped positions of elements - better suited chemical properties of elements & their compounds

assumed more elements would be discovered - left gaps

vertical columns - increasing RAM

rows - similar chemical properties

1.14 how did Mendeleev predict existence & properties of some undiscovered elements?

used gaps in table - based on properties of nearby elements

1.15 why was Mendeleev’s order not always correct?

thought he arranged elements in order of increasing RAM

not always true due to relative abundance of isotopes of some pairs of elements - affects RAM

1.16 atomic number - position in periodic table & protons

elements (in row) in order of increasing atomic number

atomic number = number of protons

1.17 periodic table arrangement

elements in order of increasing atomic number in rows - periods

elements with similar properties in same columns - groups

1.18 position of metals vs non-metals in periodic table & why

metals - left & middle

• less electrons in outer shells

• lose electrons easily (form cations)

non-metals - right

• more electrons in outer shells

• gain electrons easily (form anions)

1.19 predict electronic configurations

e.g. chlorine:

number of electrons = 17

2.8.7

1.20 how is electronic configuration related to position in periodic table?

number of occupied shells = period number

number of valence electrons = group number (group 0 = full outer shells)