C2- The periodic table 🧪

• All of the elements in a group, have similar chemical properties. This means the react in a similar way. • This is because all the elements in a group, have the same number of electrons in their outer energy shell

• Newlands arranged elements, in order of their increasing atomic weight. • And he saw every eight element, reacts in a similar way. [in a law of octaves]

• Because he ordered elements, by their atomic weight, sometimes elements were grouped together, even if they had different properties. • Therefore his ‘law of octaves’ wasn’t taken seriously by other scientists.

• Mendeleev arranged all the elements in order of their increasing atomic weight; he switched the order of specific elements if he needed to- so they fitted the pattern of other elements, in the same group. • He also left gaps in the periodic table where he thought some were missing- as he realised some elements hadn’t been discovered.

• In the modern periodic table, the elements are arranged in order of their atomic number • ; when Mendeleev developed his periodic table, protons were undiscovered- [therefore, he ordered the elements by atomic weight] • the modern periodic table has group 0 (the nobles gases); these weren’t fully discovered when Mendeleev has published his table.

• elements can appear in the wrong order, due to the presence of isotopes

• group 0 are called the noble gases

• group 0 are called the noble gases

• the noble gases are unreactive because all the nobles gases have a full outer energy level/ a full outer shell.

• the boiling points of the noble gases increase, as the relative atomic masses increase [going down the group].

• The boiling points of the noble gases increases as you go down the group. • This is because of an increase in the number of electrons in each atom, leading to greater intermolecular forces between them, which need to be overcome

• In a periodic table, metals are found in the left and centre of the periodic table.

• when metals react, they lose electrons to achieve a full outer shell/outer energy level. • This then gives them the same electronic structure as group 0: the noble gases.

• metals always form positive ions, when they lose electrons.

• group one are called the alkali metals.

• all group 1 metals have one electron in their outer energy level/outer shell

• all group one metals react rapidly with oxygen, reacting more rapidly as you move down the group.

• all group one metals react rapidly with chorine.

• group one metals react vigorously with water. • For example, lithium has a fast reaction, sodium has a very fast reaction and potassium has an extremely fast reaction water.

• because the attraction bewteen the nucleus and outer electron decreases, meaning the outer electron is easier to lose • This is because there’s a greater distance, between the positive nucleus and the negative outer electron. • Moreover, the outer electron is shielded from the nucleus, by the internal energy levels.

• increasing in reactivity, as you move down the group. • lower boiling points and melting points, as you go down the group • and a higher relative atomic mass, as you go down the group

• Mendeleev was able to predict properties of undiscovered elements, based on other elements that are in the same group. • ; scientists accepted that his table was correct, because years later after the elements were discovered, their properties matched his predictions