chemistry C2 (excluding 2.6)

development of the periodic table, electronic structures and the periodic table, group 1, group 7, trends in the periodic table.

john newland`s contribution to the development of the periodic table in 1864

• he noticed that when elements were placed in order of their atomic weights there were sometimes similarities between every 8th element.

• produced a table showing his “law of octaves”

• he did not leave gaps for undiscovered elements.

john dalton`s contribution to the development of the periodic table in 1808

he arranged the elements in order of their atomic weights

Dmitri mendleev`s contribution to the development of the periodic table in 1869

• rearranged elements into order or increasing atomic weight so that a pattern in properties could be seen

• left gaps for elements that hadnt been discovered

• predicted the properties of these undiscovered elements, and when they were discovered they had similar properties to his predictions

• because of this, his table was accepted by other scientists.

Niels bohr`s contribution to the development of the periodic table, 1913

• explained that an elements position in the periodic table is determined by its electron configuration

• discovered shells, and that elements in the same column have the same number of electrons in their outer shell

• this provided a theoretical reason why elements in the same group share similar chemical properties.

james chadwicks contribution to the development of the periodic table, 1932

• discovered the neutron.

• this proved that isotopes are simply atoms of the same element with different numbers of neutrons.

• his work finally allowed scientists to calculate accurate atomic weights, solidifying the arrangement of the periodic table today.

describe the modern periodic table

• ordered in increasing atomic number

• groups- similar chemical properties, same number of electrons in outer shell

• periods- the same number of shells

what is a group

column

what is a period

row

what are group 0 elements

very unreactive non-metal gases, noble gases

what are group 1 elements

very reactive metals, alkali metals

what are group 2 elements

metals that form ions with a 2+ charge, alkaline earth metals

what are group 7 elements

very reactive non-metals, halogens

what are transition metals

typical metals

alkali metals become going down the group

alkali metals become more reactive going down the group. also the melting points decrease and they become softer.

explain the trend in group 1

• atoms get larger down the group as they have more shells

• single electron in the outer shell is attracted less strongly to the positive nucleus

• electrostatic attraction with nucleus gets weaker

• lose the single electron more easily

how does the trend in group 1 (alkali metals) apply to postassium

more inner shells shield outer electron in potassium, so it loses outer electrons more easily.

observations during the reaction of lithium in water

• smoke+ fizzing

• floats on water, then dissolves (low density)

observations during the reaction of sodium in water

• fizzing+ smoke

• turns into a ball

• faster reaction that lithium

observations during the reaction of potassium in water

• popping sound

• smoke

• lilac flame

• floating on water

• fastest reaction

physical properties of group 7 halogens

• the melting point increases going down the group

• diatomic molecules (contain 2 of the same atom)

• the boiling points increase going down the group

• the densities increase going down the group

appearance of the halogen flourine

pale yellow gas

appearance of the halogen chlorine

green gas

appearance of the halogen bromine

orange-brown liquid (easily vaporises into a gas)

appearance of the halogen iodine

shiny grey-black crystalline solid that sublimes into a purple vapour

what is a displacement reaction

when a more reactive element displaces a less reactive element.