TOPIC 2 - BONDING, STRUCTURE AND PROPERTIES OF MATTER Flashcards
How are ions made?
When electrons are transferred
When atoms lose or gain electrons, they are trying to get a full outer shell like a noble gas (a stable electronic structure). Atoms with full outer shells are very stable.
When non-metals form ions, they gain electrons to form negative ions
The number of electrons lost or gained is the same as the charge of the ion. Eg if two electrons are loathe charge is 2+. If 3 electrons are gained the charge is 3-
What is ionic bonding?
Transfer of electrons.
When a metal and non metal react together, the metal atom loses electrons to form a positively charged ion and the non-metal gains these electrons to form a negatively charged ion. These oppositely charged ions are strongly attracted to one another by electrostatic forces. This attraction is called an ionic bond.
What are ionic compounds?
They have a regular lattice structure, called a giant ionic lattice.
The ions form closely packed regular lattice arrangement and there are very strong electrostatic forces of attraction between oppositely charged ions, in all directions in the lattice.
Give an example of an ionic compound.
Salt.
What are some properties of ionic compounds?
High melting points and high boiling points due to the many string bonds. It takes lots of energy to overcome this attraction.
When they are solid, the ions are held in place, so the compound cannot conduct electricity. When ionic compounds melt, the ions are free to move and they’ll carry an electric current.
Some ionic compounds dissolve in water. The ions delegate and are all free to move in the solution, so they’ll carry an electric current.
What is covalent bonding?
Sharing electrons.
When non-metal atoms bond together, they share pairs of electrons to make covalent bonds. S nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces, making the covalent bonding very strong.
Atoms only share electrons in their outer shells (highest energy levels)
Each single covalent bond provides one extra shared electron for each atom.
Each atom involved generally makes enough covalent bonds to fill up its outer shell. Having a full outer shell gives them the electronic structure of a noble gas, which is very stable. Covalent bonding happens in compounds of non-metals, and in non-metal elements.
What are simple molecular substances?
Made up of molecules containing a few atoms joined together by covalent bonds.
Give some examples of simple molecular substances.
Hydrogen H2 - single covalent bonds because hydrogen atoms need one more electron.
Chlorine Cl2
Oxygen O2 - double covalent bond because each oxygen atom needs two more electrons
Nitrogen N2
Methane CH4
Water H2O
Hydrogen Chlorine HCL
What are some properties of simple molecular substances?
The atoms within are held together by very strong covalent bonds. However, the forces of attraction between these molecules are very weak.
The melting and boiling points are very low Because the molecules are easily to the feeble intermolecular forces.
Most are gases or liquids at room temperature.
As the molecule gets bigger, the strength of the intermolecular forces increases, so more energy is needed to break them, and the melting and boiling increases.
They don’t conduct electricity because they are not charged, so there are no free electrons or ions.
What are polymers?
Long chains of repeating units.
There are lots of small units linked together to form a long molecule. All the atoms in a polymer are joined together by strong covalent bonds.
The intermolecular forces between polymer molecules are larger than between simple covalent molecules, so more energy is needed to separate them. This means that polymers are solid at room temperature. The intermolecular forces are still weaker than ionic or covalent bonds, so they generally have lower boiling points than ionic or giant molecular compounds.
What are giant covalent structures?
Macromolecules.
All the atoms are bonded to each other by strong covalent bonds. They have very high melting and boiling points as lots of energy is needed to break the covalent bonds between the atoms. They don’t contain charged particles os they don’t conduct electricity - not even when molten (except graphite)
What are some examples of giant covalent structures?
Diamond - 4 covalent bonds in a very tight and rigid structure.
Graphite - 3 covalent bonds to create layers of hexagons. Each carbon atom has a delocalised electron.
These are both made from carbon atoms only.
Silicon Dioxide - or silica what sand is made of. Each grain of sand is one giant structure of silicon and oxygen.
What are allotropes?
Different structural forms of the same element in the same physical state.
Talk about diamond.
An allotrope of carbon.
Has a giant covalent structure, made up of carbon atoms that each firm four covalent bonds. This makes diamond really hard.
Those string covalent bonds take a lot of energy to break and give diamond a very high melting point. It doesn’t conduct electricity because it has no free electrons or ions.
Talk about graphite.
An allotrope of carbon.
Each carbon atom forms three covalent bonds, creating sheets of carbon atoms arranged in hexagons.
There aren’t any covalent bonds between the layers - they’re only held together weakly, so they are free to move over each other. This makes graphite soft and slippery, so it’s ideal as a lubricating material.
It has a high melting point - the covalent bonds in the layers need loads of energy to break.
Only three out of each of carbons four outer electrons are used in bonds, so each carbon atom has one electron that is delocalised (free) and can move. So graphite conducts electricity and thermal energy.
