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Mangs 17

Metals like sodium, magnesium, and aluminium have a lattice structure held together by delocalised electrons, with conductivity and melting points increasing due to the number of electrons donated and the charge of metal ions. Aluminium, donating three electrons, exhibits stronger metallic bonding and better conductivity than sodium. In contrast, silicon, a semimetal with a giant covalent structure, has a high melting point but lower conductivity due to the absence of delocalised electrons, while non-metals like sulfur, phosphorus, and chlorine exist as small molecular structures.

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21 views3 pages

Mangs 17

Metals like sodium, magnesium, and aluminium have a lattice structure held together by delocalised electrons, with conductivity and melting points increasing due to the number of electrons donated and the charge of metal ions. Aluminium, donating three electrons, exhibits stronger metallic bonding and better conductivity than sodium. In contrast, silicon, a semimetal with a giant covalent structure, has a high melting point but lower conductivity due to the absence of delocalised electrons, while non-metals like sulfur, phosphorus, and chlorine exist as small molecular structures.

Uploaded by

Nyasha Mangoro
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lattice held together by a ‘sea’ of

delocalised electrons. The delocalised electrons are those

from the outermost (valence) shell. These delocalised

electrons are free to move around within the structure

of the metal. When a potential difference is applied the

delocalised electrons drift through the metal towards the

positive terminal. Both the melting point and the electrical

conductivity increase from sodium to magnesium to

aluminium. This can be explained by the number of

electrons each metal donates into the ‘sea’ of delocalised

electrons and the increasing charge on the metal ions in

the giant metallic lattice. Each sodium atom donates just

one electron, forming Na+


ions in the lattice, whereas

each aluminium atom donates three electrons, forming

Al3+ ions. This makes the metallic bonding in aluminium

stronger, as the electrostatic forces of attraction between

its 3+ ions and the larger number of negatively charged

delocalised electrons holding the giant structure together

are stronger. There are also more delocalised electrons

available to drift through the structure when aluminium

metal conducts an electric current, making aluminium a

better electrical conductor than sodium.

The element in the centre of Period 3, silicon, has

the highest melting point because of its giant molecular


structure (also called a giant covalent structure). Every

silicon atom is held to its neighbouring silicon atoms by

strong covalent bonds. However, its electrical conductivity

is much lower than the metals at the start of the period

because there are no delocalised electrons free to move

around within its structure. Silicon is classed as a

semimetal, or metalloid.

The elements to the right of silicon are all non-metallic

elements. They exist as relatively small molecules. Sulfur

exists as S8 molecules, phosphorus as P4 molecules and

chlorine as Cl2 molecules. Although the covalent bonds

within each

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