C1.07 Elements forming compounds with chemical bonds
C1.08 Electron transfer and ionic bonds
Atoms have no charge. A charged particle is called an
ion. If an atom loses an electron,
it becomes a positively charged (+) ion. An ion that is positively charged is
known as a cation. If an atom gains an electron, it becomes a negatively
charged (-) ion. An ion that is negatively is known as an anion. The
negative and positive ions attract each other to form an ionic bond.
Task C1.08 Complete the gaps in the text below:
_____ have no charge. A charged particle is called an ___. If an atom loses an
________,
it becomes a positively charged (+) ion. An ion that is positively charged is
known as a ______. If an atom gains an electron, it becomes a negatively
charged (-) ion. An ___ that is negatively is known as an anion. The
negative and positive ions attract each other to form an _____ bond.
C1.09 The formation of sodium and chloride ion
Animated ion formation. (needs Powerpoint)
Task C1.09a Draw atoms and ions for lithium,
potassium, fluorine, magnesium, oxygen, sulfur and aluminium.
Task C1.09b Draw diagrams of ionic bonding in LiF, KF, LiCl, NaF, MgCl2,
AlF3, MgO, MgS, Na2O and Al2O3.
C1.10 Physical properties of giant ionic structures
Ionic bonds form when metal and non-metal atoms join. A substance with
ionic bonding has an ionic structure. Each ion is firmly held in place
by strong ionic bonds so they have high melting and boiling points. If
melted, charged ions become free to carry an electric current. The ions
also become free if dissolved in water so solutions are also electrolytes. The solids are insulators because
the ions are not free to move and cannot carry a current. Sodium chloride
NaCl, and magnesium oxide MgO are good examples.
Task C1.10 Pick out the substances which are (a)
ionic (b) have covalent bonds (c) have high melting points (d) conduct
electricity when molten: sodium chloride, sulfur dioxide, magnesium oxide, iron
fluoride, carbon dioxide, NaBr, H2O, NH3, Al2O3,
KCl.
C1.11 Covalent bonds and electron sharing
Non-metal atoms join using covalent bonds. When a covalent bond is formed,
atoms share their electrons. The atoms then have full shells. One covalent bond
needs one shared electron from each atom. Each atom involved has to make
enough covalent bonds to fill up its outer shell. Sharing electrons is
called covalent bonding. Below is a diagram to
show hydrogen gas (H2).
C1.12 Dot and cross diagrams
Task C1.12: Draw atoms of F, H, O, N and C.
Draw a dot and cross diagram for fluorine F2, hydrogen fluoride
HF, water H2O, ammonia NH3, methane CH4, oxygen
O2, nitrogen N2, ethene C2H4.
C1.13 Physical properties of simple molecular substances
Simple Molecular Substances have
low melting and boiling points and most are gases or liquids at room temperature.
This is because of weak forces between the molecules. Molecular substances
do not conduct electricity, because there are no ions. E.g. water.
Draw diagrams to show how the molecular structures for the
following might look: fluorine F2,
hydrogen fluoride HF, water H2O, ammonia NH3, methane CH4,
oxygen O2, nitrogen N2
C1.14 Giant structures with covalent bonds
In giant covalent structures all
the atoms are bonded to each other by strong covalent bonds so they have
very high melting and boiling points. They do not usually conduct electricity
even if in the liquid state. Diamond and graphite are two examples, which
are made from carbon atoms. These two different types of the same element
are called allotropes.
Diamond: Each carbon atom forms four covalent bonds in a very rigid giant covalent structure.
Diamond:
Graphite: exists as layers of carbon atoms each held in
place by three strong covalent bonds. Each layer is held to the one above
it by weak bonds.
C1.15 Physical properties of giant covalent structures
Giant molecular structures
have very high melting points because all atoms are held firmly in place
by strong covalent bonds. In graphite each carbon atom is held in place
by three strong covalent bonds which gives graphite a high melting point.
In diamond 4 strong covalent bonds holds each atom in place. This also gives
diamond a very high melting point. The four bonds make
diamond very hard. Graphite has weak bonds between layers so the layers
slip over each other making graphite soft.
They do not usually conduct electricity even when molten because there are no charged particles to carry the current. There are free electrons between layers in graphite so it conducts electricity.
C1.16 Explaining differences between properties
Simple molecular substances like water have weak bonds between molecules so melt
at low temperatures because little energy is needed to separate the
molecules. Giant covalent structures like diamond have strong covalent
bonds holding each atom in place. They melt at high temperatures because a
lot of energy is needed to break these strong bonds.
TaskC1.16
