Bonding and structure Flashcards
Ionic bonding
Metal and non-metal
Happens when electrons are transferred form one atom to another
Elements in the same group have the same number of outer electrons so they all have to loose or gain the same number of electrons to gain a full outer shell
Generally, the charge on a metal ion is equal to its group number
On a non-metal it’s equal to its group number minus 8
Electrostatic attractions are the forces that hold positive and negative ions together
Dot and cross diagrams in bonding
Only show outer shell electrons
In ionic bonding it shows all the electrons in brackets as it’s showing the movement of electrons
What is a lattice
A regular structure
Within the lattice, ions with different charges attract and those with the same charge repel. The ions arrange each other to maximise attraction and minimise repulsion
Ionic compound properties
They conduct electricity when molten or dissolved because the ions are free to move whereas in a solid they’re held by strong ionic bonds
They have high melting points as they’re held together by strong electrostatic forces which take a lot of energy to overcome
They’re often soluble in water as water is polar so the water molecules pull ions away from the lattice causing it to dissolve
Dative covalent bonding
Where both electrons come from one atom
E.g. ammonium ion NH₄+
Shown in diagrams by an arrow pointing away from the donor atom
Covalent bonding
When atoms share electrons so they’ve got a full outer shell
The positive nuclei are electrostatically attracted to the shared electrons as there’s a repulsion between the nuclei. For the covalent bond to be maintained this has to balance
Happens between non-metals
Simple molecular substances
Low melting and boiling points as they’re usually liquids or gases at standard temperature and pressure
To melt or boil a simple molecular compound you only have to overcome the intermolecular forces between the molecules which are weak compared to ionic or covalent bonds
They don’t conduct electricity because there are no charge carriers
They’re usually insoluble in water or at least only slightly soluble as the polar water molecules are more attracted to each other
Exceptions of covalent bonding
Boron trifluoride only has six electrons in its outer shell
A few compounds can use the d orbital to expand the octet, meaning they can have more than 8 electrons in their outer shell e.g. sulfur hexafluoride
Properties of giant covalent
Very high melting points as their strongly covalently bonded which takes a lot of energy to overcome
Often hard because of the strong bonds throughout the lattice arrangement
Good thermal conductors as vibrations can travel throughout the lattices
Insoluble as the covalent bonds mean atoms are more attracted to neighbours in the lattice than to solvent molecules
Insoluble in polar solvents shows that they don’t contain ions
Can’t conduct electricity as there are no charged ions or free electrons, all the bonding is held in localised electrons
Why can graphite (a form of carbon ) conduct electricity?
Carbon atoms form sheets with each C atom sharing three of its outer shell electrons to three other C atoms. This leaves the fourth outer electrons in each atom fairly free to move between the sheets and therefore conduct electricity
The individual sheets are held together by relatively weak forces.
Giant metallic lattice
The electrons in the outermost shell of the metal atoms are delocalised (free to move). This leaves a positive metal ion which are attracted to the delocalised negative electrons. They form a lattice of closely packed positive ions in a sea of delocalised electrons
Properties of giant metallic lattice
High melting points because of the strong metallic bonding, with the number of delocalised electrons per atom affecting the melting point. The more there are the stronger the metallic bonding
The size of the metal ion and its structure also affect melting point
Metals can be shaped and are ductile as the metal ions can slide over each other
Good electrical conductors because the delocalised electrons are free to move and can carry a current. Impurities can reduce electrical conductivity by reducing the number of electrons free to move – the electrons transfer to the impurities and form anions
The delocalised electrons can pass kinetic energy to each other making metals good thermal conductors
Insoluble, expect in liquid metals, because of the strength of the metallic bonds
