Unit 1: Section 3 - Bonding CDS * Flashcards
ionic bonding covalent bonding shapes of molecules polarisation and intermolecular forces
what is formed when different elements bond together?
a compound
what are the 2 main types of bonding in compounds?
ionic
covalent
how are ions formed?
when 1 or more electrons are transferred from 1 atom to another.
the 2 ions are totally distinct from 1 another
what are the simplest ions?
single atoms which lose or gain electrons to get a full outer shell
examples of simple ions:
sodium atom loses 1 electron, Na+
magnesium loses 2, Mg2+ (Mg –> Mg2+ + 2e-)
chlorine gains 1, Cl-
oxygen gains 2, O2- (O + 2e- –> O2-)
how do you know what ion is formed from an atom?
every element in a group has the same number of outer electrons. so they lose or gain the same number of electrons, so have the same charge
what charge ions does each group have?
Group 1 = 1+ ions
Group 2 = 2+ ions
Group 6 = 2- ions
Group 7 = 1- ions
what are compound ions?
ions that are made up of groups of atoms with an overall charge
what are the formulas of some compound ions?
sulfate = SO4 2- hydroxide = OH- nitrate = NO3 - carbonate = CO3 2- ammonium = NH4 +
how can you work out the formula of an ionic compound from the charges of individual ions?
the charges must balance out so if one ion is 1- and the other 2+ you need to of the 1- ion to cancel out the other
in general swapping the charges of the ions to become the number of the opposite ions works
e.g. X2- and Y3+
X3Y2
what are ionic crystals?
giant lattices of ions
what is a giant ionic lattice?
lattice - a regular structure
giant - it’s made up of the same basic unit repeated over and over
what is the structure of sodium chloride?
the Na+ and Cl- ions are packed together. the sodium chloride lattice is cube shaped - different ionic compounds have different shaped structures, but they’re all still giant lattices
what properties do ionic compounds have from their ionic structure?
conduct electricity when they’re molten or dissolved - but not when they’re solid
ionic compounds have high melting points
ionic compounds tend to dissolve in water
why do ionic compounds conduct electricity when fluid but not solid?
the ions in a liquid are free to move and carry a charge
in a solid the ions are fixed in position by strong ionic bonds
why do ionic compounds have high melting points?
giant ionic lattices are held together by strong electrostatic forces. it takes loads of energy to overcome these forces, so melting points are very high
what is the melting point of sodium chloride?
801 *C
why do ionic compounds tend to dissolve in water?
water molecules are polar - part of the molecule has a small negative charge and other bits have small positive charges. these charged parts pull ions away from the lattice, causing it to dissolve
how do molecules form?
when 2 or more atoms bond together - they could be the same or different
they’re held together by strong covalent bonds
what does a single covalent bond contain?
a shared pair of electrons
what happens in covalent bonding?
2 atoms share electrons, so they’ve both got full outer shells of electrons. both the positive nuclei are attracted electrostatically to the shared electrons
what do giant covalent structures have?
a huge network of covalently bonded non-metal atoms, sometimes called macromolecular structures
why can carbon atoms form giant covalent structures?
because they can each form 4 strong, covalent bonds.
what are 3 examples of giant covalent structures?
graphite
diamond
SiO2