1.3 Bonding Flashcards
Ions
An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons.
Negative ions are called anions. (Non-metals)
Positive ions are called cations. (Metals)
Deducing subatomic particles in ions
An atom is neutral and has no overall charge.
A positively charged ion has lost electrons and therefore has fewer electrons than protons.
A negatively charged ion has gained electrons and therefore has more electrons than protons.
Ionic bonding
Ionic compounds consist of a metal bonded to a non-metal via electron transfer.
The metal atom loose electrons to become a positively charged ion (cation) and obtain a full outer shell of electrons becoming stable.
The non-metal atom gain electrons to become a negatively charged ion (anion) and obtain a full outer shell of electrons becoming stable.
They form regular shaped giant ionic lattices in which strong electrostatic forces act in all directions.
Properties of ionic bonds
High melting and boiling point - Strong electrostatic forces of attraction between opposite charged ions throughout the giant structure.
They are hard but brittle - Strong level of attraction, when layers slide ions of the same charge align and the structure breaks.
They are generally soluble in water - Ions are attracted to the water molecules and the attraction breaks the lattice apart.
They never conduct electricity in a solid state - The ions are held in position and are not free to move.
They often conduct electricity as a liquid (when molten or dissolved in water) - the ions are free to move.
Covalent bonding
Covalent compounds are formed between 2 or more non metal elements.
A covalent bond consists of a shared pair of electrons.
There are two types of covalent substances.
Each atom donates 1 electron to the shared pair of electrons, which make up the covalent bond.
By doing this each atom has the same electron structure as a noble gas.
Simple covalent
A simple covalent bond is formed between two or more non metals.
These are composed of tiny separate particles called molecules.
These contain several atoms bonded strongly together by covalent bonds however, the forces between molecules are weak intermolecular forces.
Properties of simple covalent
Melting and boiling points are low. many are either liquid or gaseous at room temperature - the covalent bonds within these molecules are strong but the intermolecular force between molecules are weak. the intermolecular forces break when a substance melts or boils.
Electrical conductivity is poor - there are no ions or electrons that are free to move.
Insoluble in water - they are not charged, as oxygen is negative and hydrogen is positive, (opposite attracts).
Giant covalent
Giant covalent structures consist of many non-metals atoms bonded to other non-metal atoms via strong covalent bonds.
Diamond and graphite are both forms of the element carbon. both their structures contain many thousands of carbon atoms joined together by strong covalent bonds. although both substances are made up of the same atoms they have different physical properties.
Structure of diamonds
Each carbon atom is joined together by 4 other carbon atoms by strong covalent bonds in a tetrahedron shape. there are strong covalent bonds throughout the entire lattice.
Properties of diamonds
Very high melting and boiling points - there are lots of strong covalent bonds throughout the giant structure which require lots of energy to break apart therefore increasing the melting and boiling point.
Hardness - very hard due to strong covalent bonds throughout the giant structure, so they are used in drill tips.
Electrical conductivity - no electrical conductivity as all the electrons are used in the covalent bonds.
Structure of graphite
Each carbon atom is joined by 3 other carbon atoms by strong covalent bonds within a layer, however there are weak intermolecular forces of attraction between layers which allow layers to slide. There are also delocalised electrons between layers which are free to move.
Properties of graphite
Very high melting and boiling points - there are lots of strong covalent bonds throughout the giant structure which require lots of energy to break apart therefore increasing the melting and boiling point.
Hardness - soft due to weak intermolecular forces between layers allowing them to slide.
Electrical conductivity - very good as it has delocalised electrons between layers that can move freely.
Silicon dioxide (sand)
Sand has very similar properties to diamond instead of containing carbon atoms it contains silicon and oxygen atoms.
Metallic bonding
Metals consist of metal atoms that are held together strongly by metallic bonding
Within the metal lattice, the atoms lose their valence electrons and become positively charged.
The valence electrons no longer belong to any metal atom and are said to be delocalised, creating what is known as a sea of free electrons.
The free electrons move freely in between the positive metal atoms.
Properties of metals
Metals have high melting and boiling points - There are many strong metallic bonds in giant metallic structures. A lot of heat energy is needed to overcome forces and break these bonds.
Metals conduct electricity and heat - There are free electrons available to move and carry charge. Electrons entering one end of the metal cause a delocalised electron to displace itself from the other end. Hence electrons can flow so electricity is conducted.
Metals are malleable and ductile - Layers of positive ions can slide over one another and take up different positions. Metallic bonding is not disrupted as the valence electrons do not belong to any particular metal atom so the delocalised electrons will move with them. Metallic bonds are thus not broken and as a result metals are strong but flexible. They can be hammered and bent into different shapes without breaking.
Alloys
Alloys such as bronze and stainless steel are mixtures of metals where the different metals are metallically bonded in a giant metal lattice. they are generally tougher and stronger than pure metals as the extra metal disrupts the shift of the atoms reducing malleability.
