GCSE Chemistry - Properties of Simple Molecular Substances & Giant Covalent Structures #17
Summary
TLDRThis video explores covalent bonding in non-metals, distinguishing between simple molecular substances and giant covalent structures. Simple molecular substances like chlorine have strong covalent bonds within molecules, but weak intermolecular forces, leading to low melting and boiling points. In contrast, giant covalent structures such as diamond and silicon dioxide exhibit high strength and melting points due to extensive covalent bonding. The video also notes that simple molecular substances don't conduct electricity, while graphite is an exception among giant covalent structures, with unique conductivity properties.
Takeaways
- 🔬 Non-metals form covalent bonds by sharing electrons to achieve full outer shells.
- 🌡️ Simple molecular substances like chlorine have strong covalent bonds within molecules but weak intermolecular forces.
- 💧 Melting or boiling simple molecular substances requires overcoming weak intermolecular forces, not the covalent bonds.
- 📉 The boiling point of simple molecular substances increases as you go down the group due to larger molecules and more intermolecular forces.
- 🔋 Simple molecular substances do not conduct electricity because they lack free electrons and have no overall charge.
- 💠 Giant covalent structures consist of a vast network of covalently bonded non-metal atoms, forming regular repeating lattices.
- ⚒️ Diamond, graphite, and silicon dioxide are examples of giant covalent structures, known for their strength and high melting points.
- ❌ Giant covalent structures generally do not conduct electricity, except for graphite, which is discussed in more detail in another video.
- 🏖️ Silicon dioxide, also known as silica, is the main component of sand and is composed of silicon and oxygen in a 1:2 ratio.
- 📚 Understanding the distinction between simple molecular substances and giant covalent structures is key to grasping their properties and behaviors.
Q & A
What are covalent bonds and how do they form in non-metals?
-Covalent bonds are formed when non-metal atoms share electrons so that all atoms have full outer electron shells. This bonding allows the atoms to achieve stability by completing their valence electron configurations.
What is the difference between simple molecular substances and giant covalent structures?
-Simple molecular substances are small molecules made up of a few covalently bonded atoms, whereas giant covalent structures consist of a vast network of covalently bonded non-metal atoms arranged in a repeating lattice.
Why do simple molecular substances like chlorine require low temperatures to melt or boil?
-Simple molecular substances require low temperatures to melt or boil because only the weak intermolecular forces between molecules need to be overcome, not the strong covalent bonds within the molecules.
How do the melting and boiling points of halogens change as you go down the group in the periodic table?
-The melting and boiling points of halogens increase as you go down the group because the molecules get larger, resulting in more intermolecular forces and thus requiring more energy to break them.
Why don't simple molecular substances conduct electricity?
-Simple molecular substances do not conduct electricity because they lack free electrons and the molecules themselves have no electric charge. Conductivity requires free-moving electrons or ions.
What are the characteristics of giant covalent structures in terms of strength and conductivity?
-Giant covalent structures are very strong and have high melting and boiling points due to the extensive network of covalent bonds. They generally do not conduct electricity because they do not contain charged particles.
What is the difference between diamond and graphite in terms of their electrical conductivity?
-Diamond does not conduct electricity, while graphite does due to the presence of delocalized electrons in its structure, which allows for electrical conductivity.
What is silicon dioxide, and what is its common name?
-Silicon dioxide is a giant covalent structure composed of silicon and oxygen atoms in a 1:2 ratio. It is commonly known as silica and is the main component of sand.
Why are the structures of giant covalent structures described as repeating lattices?
-The structures of giant covalent structures are described as repeating lattices because their arrangement of atoms is regular and periodic, with the same pattern repeating throughout the material.
What is the significance of the ratio of silicon to oxygen atoms in silicon dioxide?
-The ratio of one silicon to two oxygen atoms in silicon dioxide indicates the chemical formula of the compound, which is SiO2, and is crucial for understanding its structure and properties.
Outlines
🔬 Covalent Bonds and Molecular Structures
This paragraph introduces covalent bonding, where non-metals share electrons to achieve full outer shells. It distinguishes between simple molecular substances, like chlorine and ammonia, which form small molecules, and giant covalent structures like diamond, graphite, and silicon dioxide. The strength of covalent bonds is highlighted, noting that melting or boiling these substances involves overcoming intermolecular forces rather than breaking covalent bonds. The paragraph also touches on the properties of simple molecular substances, such as low melting and boiling points and their inability to conduct electricity due to the lack of free electrons.
Mindmap
Keywords
💡Covalent Bonds
💡Simple Molecular Substances
💡Intermolecular Forces
💡Giant Covalent Structures
💡Melting and Boiling Points
💡Conductive Properties
💡Halogens
💡Silicon Dioxide
💡Lattice Structures
💡Electron Sharing
Highlights
Non-metals form covalent bonds by sharing electrons to achieve full outer shells.
Simple molecular substances are small molecules like chlorine or ammonia.
Giant covalent structures are formed by non-metals bonding to create large networks.
Covalent bonds are strong, requiring significant energy to break.
Melting or boiling simple molecular substances involves breaking intermolecular forces, not covalent bonds.
Chlorine boils at -34 degrees Celsius due to weak intermolecular forces.
Intermolecular forces increase in strength with the size of molecules.
Melting and boiling points of halogens increase down the group due to larger molecules and more intermolecular forces.
Brominated boils at 59 degrees Celsius, and iodine at 184 degrees Celsius, illustrating the trend.
Simple molecular substances do not conduct electricity due to the lack of free electrons.
Giant covalent structures consist of a vast number of covalently bonded non-metal atoms.
Diamond, graphite, and silicon dioxide are examples of giant covalent structures.
Giant covalent structures have high melting and boiling points due to the strength of covalent bonds.
Graphite is an exception to the non-conductive nature of giant covalent structures.
Silicon dioxide, also known as silica, is the main component of sand and has a 1:2 ratio of silicon to oxygen atoms.
Simple molecular substances are joined by weak intermolecular forces, while giant covalent structures have strong, regular repeating lattices.
The key takeaway is the distinction between the properties of simple molecular substances and giant covalent structures.
Transcripts
we've already seen in other videos that
non-metals can join together by covalent
bonds
in which they share electrons so that
all of the atoms have full outer shells
sometimes this results in small
molecules such as chlorine or ammonia
and we call these simple molecular
substances
in other cases though non-metals bond
covalently to form giant covalent
structures
like diamond graphite or silicon dioxide
and in today's video we're going to look
at the respective properties of each of
these
and then finish up by taking a closer
look at the structure of silicon dioxide
now the first thing to know is that
covalent bonds are really strong
which means that a lot of energy is
going to be needed to break apart any
atoms that conveniently bonded to each
other
so if we consider a simple molecular
substance like chlorine the atoms within
each molecule will be strongly bonded
together
however in order to melt or boil
chlorine we actually don't break these
strong covalent bonds
instead we only need to break the weak
forces that exist between different
molecules
which we call intermolecular forces
because of this we only need very low
temperatures to melt or boil simple
molecular substances
for example chlorine boils at -34
degrees celsius
although these intermolecular forces are
individually quite weak
the more of them that a molecule has the
stronger the overall attraction is going
to be
for example let's compare the halogens
chlorine bromine and iodine
because we're going down the group the
atoms and thus molecules are getting
bigger
so there'll be more intermolecular
forces between them
this in turn means that more energy will
be required to break them all
so the melting and boiling points should
increase as you go down the group
which they do
as bromine has a boiling point of 59
degrees and iodine doesn't boil until
184 degrees
there's no need to remember these
specific numbers
you just need to understand that the
boiling point increases as you go down
the group because the molecules get
larger so there are more intermolecular
forces between them
another property to note is that simple
molecular substances don't conduct
electricity
because there are no free electrons and
the molecules themselves have no
electric charge
you'll see this point again and again in
chemistry
in order to conduct electricity or heat
substances have to have some electrons
or ions that are free to move about
so moving on to giant covalent
structures
these are made of huge numbers of
non-metal atoms that are all bonded to
each other by covalent bonds
and they're generally arranged into
regular repeating lattices
which just means that their structure
kind of repeats over and over
the three important examples are diamond
graphite and silicon dioxide
the main things to remember about these
structures is that they're very strong
and they have high melting and boiling
points
because we'd have to break all of these
strong covalent bonds in order to melt
them
the other property to know is that they
generally don't conduct electricity
because they don't contain any charged
particles
even when they're molten
an exception to this though is graphite
which we take a closer look at in
another video along with diamond which
are both made of carbon atoms
silicon dioxide on the other hand is
made of silicon and oxygen atoms in a
ratio of one to two
it's also known as silica and is the
main component of sand
you won't have to draw it but you do
need to be able to recognize giant
covalent structures like this
now the key thing to take away from this
video is that simple molecular
substances are small molecules that are
made up of just a few conveniently
bonded atoms
and the separate molecules are only
joined together by weak intermolecular
forces
meanwhile in giant covalent structures
all of the atoms are covalently bonded
in regular repeating lattices which
makes them much stronger and gives them
much greater melting and boiling points
anyway that's it for now so hope you
enjoyed it and we'll see you next time
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