Ions, Metals and Covalent Compounds

• Vertical columns are called groups and horizontal rows are called periods
• Elements in groups have the same number of valence electrons as their group number (magnesium in group 2 and has 2 valence electrons) 
• Elements in periods have the same number of shells (nitrogen and oxygen are both in period 2 and have 2 shells)
• The mass number of the element is the larger number and is usually rounded to 2 decimal places
• The atomic number is the smaller number and gives the number of protons (and electrons)
• The mass number is how much 1 mole (6x0.22^23) of the element is

• Isotopes have the same number of protons (and electrons) but have a different number of neutrons
• They have identical chemical properties because the number of electrons/protons are the same but different physical properties (such as mass, radioactivity etc)
• Isotopes can be used for carbon dating 
• Some examples of isotopes are carbon-13 and carbon-14 

Ionic Bonding

• An ion is a charged atom, the atom is charged because it has lost or gained electrons
• Atoms lose or gain electrons to get a full valence (outer) shell 
• When an atom loses an electron it becomes positive and is called a cation 
• When an atom gains an electron it becomes negative and is called an anion 

Ionic Compounds

• Ionic compounds have one negative and one positive ion (usually one metal and one non-metal atom)
• You can tell if an element is positive or negative by using the periodic table and looking at the group number 
• The charges from the positive and negative ions have to balance out
• In solid form, ionic compounds can't conduct electricity because there aren't any free moving electrons 
• However in a solution, ionic compounds can conduct electricity because the ions are free to move
• Ionic compounds have high melting and boiling points because the electromagnetic attraction is strong

Metallic Bonding

• Metal atoms lose electrons from their valence shell 
• These lost electrons are called delocalised electrons and form a sea of delocalised electrons which is negatively charged
• This negatively charged sea of electrons are around the postive nuclei and act like a glue 
• The metallic bonding is a strong, non-directional, electrostatic attraction between the positive nuclei of the atom and the delocalised electrons 

Metal Compounds

• Metal compounds can conduct electricity because there is a sea of delocalised electrons so the electrical current can pass through
• They also have high melting and boiling points because the electrostatic forces between the atoms are strong so it takes more energy to break them 

• Covalent bonding is when non-metal atoms bond to each other by sharing an electron so they can have a full valence (outer) shell
• Covalent compounds can't conduct electricity because there are no free moving electrons or delocalised electrons
• They also have low melting and boiling points because the electrostatic attraction between the molecules is weak 

• Covalent Lattices are non-metal atoms that are covalently conded in massive continuous structures
• These structures can be in 3D layers (diamond) or 2D layers (graphite)
• Apart from graphite, covalent lattices can't conduct electricity because there are no free moving electrons or delocalised electrons
• Covalent lattices have very high melting and boiling points because the electrostatic attraction is very strong 

Diamond

• Diamond is made of carbon atoms that are covalently bonded to 4 other carbon atoms in a 3D structure 
• A large amount of heat energy is needed to break the covalent bonds between the carbon atoms

Silica (Silicon Dioxide)

• Every silicon atom is covalently bonded to 4 oxygen atoms in a 3D structure 
• Has the same properties as diamond 

Graphite

• Each carbon atom is covalently bonded to other carbon atoms in a 2D structure
• There is a layer of electrons in between the layer of carbon atoms which is why graphite can conduct electricity
• This layer of electrons allows the layer of carbon to slide over each other which is why graphite is quite soft
• The covalent bonds are still strong so graphite has a high melting/boiling point 

• Trigonal Pyramid has 4 densities, 3 bonds and 1 lone pair 
• Tetrahedral has 4 densities, 4 bonds and 0 lone pairs
• Linear has 2 densities, 2 bonds and 0 lone pairs 
• Bent has 4 densities, 2 bonds and 2 lone pairs