2.1 Chemical bonds & types of bonding Flashcards
What is ionic bonding?
Ionic bonding is the electrostatic attraction between positive and negative ions.
It is a relatively strong attraction.
How are ionic compounds
held together?
● They are held together in a giant lattice.
● It’s a regular structure that extends in all directions in a
substance.
● Electrostatic attraction between positive and negative ions holds the structure together.
State the properties of ionic substances
● High melting and boiling point (strong electrostatic forces between
oppositely charged ions)
● Do not conduct electricity when solid (ions in fixed positions).
● Conduct when molten or dissolved in water - ions are free to move.
Give 3 examples of positive ions and
3 examples of negative ions.
What is important when working out
a formula of an ionic compound?
E.g. Positive: Na+, Mg2+, Al3+, Ca2+, Rb+
Negative: Cl−, Br−, SO42−, NO3−, OH−
(chloride, bromide, sulfate, nitrate,
hydroxide).
Ionic compounds are electrically neutral, i.e. positive and negative charges balance each other.
How are ionic compounds
formed? Explain using MgO
Reaction of a metal with a non-metal.
Electron transfer occurs - metal gives away its outer shell electrons to
non-metal.
Mg is in Group II, so has 2 available outer shell electrons.
O is in Group VI, so can accept 2 electrons to get a full outer shell
configuration.
Mg becomes Mg2+ and O becomes O2− (oxide).
What is a covalent bond?
A covalent bond is a shared pair of electrons between two atoms.
Describe the structure and
properties of simple molecular
covalent substances
● Do not conduct electricity (no ions)
● Small molecules
● Weak
intermolecular forces, therefore:
● Low melting and boiling points
How do intermolecular forces change as the mass/size of the molecule increases?
They increase. That causes melting/boiling points to increase as well (more
energy needed to overcome these forces).
What are polymers? What are thermosoftening polymers?
Polymers are very large molecules (>100s, 1000s of atoms) with atoms linked by covalent bonds.
Thermosoftening polymers - special type of polymers; they melt/soften when heated. There are no bonds between polymer chains. Strong intermolecular forces ensure that the structure is solid at room temperature. These forces are overcome
with heating - polymer melts.
What are giant covalent
structures? Give examples
● Solids, atoms covalently bonded together in a giant lattice.
● High melting/boiling points – strong covalent bonds.
● Mostly don’t conduct electricity (no delocalised e−)
● Diamond, graphite, silicon dioxide.
What is metallic bonding?
Forces of attraction between delocalised electrons and nuclei of metal
ions.
Describe the properties of
metals
● High melting/boiling points (strong forces of attraction)
● Good conductors of heat and electricity (delocalised electrons)
● Malleable, soft (layers of atoms can slide over each other whilst maintaining
the attraction forces)
What are alloys? Why are they harder than pure
metals?
Alloys:
● Mixtures of metal with other elements, usually metals
● Different sizes of atoms distorts the layers, so they can’t slide over each other, therefore alloys are harder than pure metals
