TOPIC 1- key concepts Flashcards
Ions
Charged particles (single/groups of atoms)
Negative ions
(Anions) form when atoms gain electrons.
Positive ions
Cations.
Form when atoms lose electrons.
Charge
The number of electrons lost/ gained
-2 = 2 electrons gained
+2 = 2 electrons lost
Groups of elements that most readily form ions
1, 2, 6 and 7
Metals charge
Positive
Nonmetals charge
Negative ions
Group 1 elements charge?
Group 2 elements charge?
Group 6 elements charge?
Group 7 elements charge?
+1
+2
-2
-1
What are ionic compounds made up of?
A positive/negative part. The positive balances out the negative.
Overall charge of ionic compounds
Zero
Ionic bonding
Transfer of electrons between a metal and nonmetal. The metal atom loses an electron to form a positive ion (cation) and the nonmetal gains these electrons to form a negative ion (anion). These oppositely charged ions are strongly attracted to each other via electrostatic forces.
How do you show how ionic compounds are formed?
Dot and cross diagrams
Structure of ionic compounds
They have a regular, giant ionic lattice structure due to strong electrostatic forces between oppositely charged ions.
Properties of ionic compounds
High melting/boiling points (due to strong attraction between ions that require much energy to break).
Conducts electricity when dissolved/molten. (Because the ions are then free to move and so will carry and electric current)
Soluble
Advantages of 2D representations (displayed formulas)
Simple
Good at showing what atoms something contains and how they’re connected.
Disadvantages of 2D representations (displayed formulas)
Don’t show the shape of the substances.
Don’t show the size of the atoms.
Advantages of dot and cross diagrams
Useful for showing how molecules are formed and where the electrons in the bonds/ions come from.
Disadvantages of dot and cross diagrams
Don’t show size /arrangement of atoms.
Advantages of 3D models
Show arrangement of ions
Disadvantages of 3D models
Only show outer layer of substance
Disadvantages for ball and stick models
Misleading as make out that there are big gaps between atoms (actually where electron clouds interact).
Don’t show correct scales of atoms/ions.
Advantages of ball and stick models
Help to visualise
More realistic than 2D
Covalent bond
A strong bond formed when a pair of electrons is shared between 2 atoms.
Simple covalent molecular substances
Substance made up of molecules containing a few atoms joined by covalent bonds.
Eg: H2, HCl, H2o
Properties of simple molecular substances
Molecules are held together by v strong covalent bonds but have weak intermolecular forces (forces of attraction) between them. This means they have LOW MELTING/BOILING POINTS as intermolecular forces require very little energy to break them.
This also means that they are mostly gases/liquids at room temp.
They DONT CONDUCT ELECTRICITY.
What happens to simple molecular substances as they get bigger?
Boiling points increase as more intermolecular forces need more energy to break.
What are polymers made out of?
They are molecules made out of long chains of covalently bonded carbon atoms and form when small molecules called monomers join together. (seb is a geek).
Eg polyethylene
Giant covalent structures
Structures with all atoms bonded by strong covalent bonds. For example, diamond, graphite, graphene and C60.
Properties of giant covalent structures
HIGH MELTING/BOILING POINTS (much energy is needed to break the covalent bonds)
GENERALLY DONT CONDUCT ELECTRICITY (apart from graphite and graphene)
INSOLUBLE
How many covalent bonds does each carbon atom have in a diamond?
What are some of the properties of diamond?
Four.
Have v high boiling/melting points. V hard (due to rigid lattice structure) which enables it to be used to strengthen cutting tools.
Doesn’t conduct electricity (no free electrons/ions).
How many covalent bonds do each carbon atom have in graphite? How does this affect its structure?
Three, this means that its arranged in sheets of hexagons.
What are the layers in graphite held together by? How does this affect its properties?
Only held together by weak intermolecular forces, this means that they are free to move over each other. Therefore graphite is slippery, soft and an ideal lubricating material.
Properties of graphite
Soft, slippery High melting point (covalent bonds require much energy) Conducts electricity (because 3/4 electrons are used in bonding, meaning each carbon has one delocalised electron) >> is used as electrode
Fullerene
Molecule of carbon, shaped like closed tubes/hollow balls.
Eg graphene or C60
What’s graphene
One layer of graphite (sheet of carbon atoms joined in hexagons w three covalent bonds per carbon atom)
One atom thick, is a 2D compound.
Buckminsterfullerene
A hollow sphere made up of 20 hexagons and 12 pentagons. Stable molecule which forms soft born/black crystals.
Uses of fullerenes
Can be used to ‘cage’ other molecules so can be of use in drug delivery to cells in body.
Can be used as industrial catalysts.
Can be used to strengthen materials without adding weight (tennis rackets)
Properties of fullerenes
Large surface area to volume ratio
High tensile strength
Semiconductor of electricity