Bonding, Structure and Properties of Matter Flashcards
What are the three types of strong chemical bonds?
- Ionic bonds
- Covalent bonds
- Metallic bonds
What is an ion?
Where do ionic bonds occur?
Atoms that have gained or lost electrons
Between positive and negative ions
Do ions have an overall charge?
Yes
What do ions have the same electronic structure as?
Noble gas - complete outer shell of electrons
What does ionic bonding involve?
The transfer of electrons from metal atoms to non-metal atoms
Describe what the charge of metal and non-metal atoms when they react to become ions.
Metals = lose electrons and become positively charged
Non-metals = gain electrons and become negatively charged
What is an ionic bond?
A strong electrostatic force of attraction between the positive metal ion and the negative non-metal ion
Practice question:
Describe what happens when two sodium atoms react with one molecule of chlorine.
Sodium has 1electron in outer shell
Chlorine has 7 electrons in outer shell
One chlorine molecule = 2 chlorine atoms
Sodium atom transfers one electron to one of chlorine atoms
All now have 8 electrons in outer shell
Become Na+ and Cl-
2Na + Cl2 —— 2NaCl
What are ionic compounds?
Giant structures of ions
What are ionic compounds held together by?
Strong forces of attraction (electrostatic forces) that act in all directions between oppositely charged ions
Name some properties of ionic compounds.
- High melting points
- Do NOT conduct electricity when solid because ions cannot move
- Do conduct electricity when molten or in solution because the charged ions are free to move about and carry their charge
Why do metals form positively charged ions?
Because they lose electrons in order to form ions
Why do ionic compounds have high melting and boiling points?
Ionic bonds are very strong and therefore requires a lot of energy to overcome them
Where does metallic bonding occur?
In metallic elements such as iron and copper
Alloys such as stainless steel
Describe the structure of metals.
A giant 3D lattice in which electrons in the outer shell are delocalised
What is a metallic bond?
The attraction between the positive ions and the delocalised negatively charged electrons
Why are metals good thermal and electrical conductors?
The delocalised electrons can move freely and transfer energy
Why do most metals have high melting and boiling points?
Metallic bonds are very strong meaning that a lot of energy is required to break them
Why can metals be bent and hammered into different shapes?
The layers are able to slide over each other quite easily
Practice question:
Why is copper used to make water pipes?
- It’s an interactive metal, so it does not react with water
- It can be easily shaped
What is an alloy?
Mixtures that contain a metal and at least one other element
Why are pure metals rarely used?
They are to soft
In alloys, what does the added element do to the arrangement of the metal atoms?
It disturbs the regular arrangement so the layers do not slide over each other so easily
What is steel?
A very useful alloy made from iron
When iron oxide is reduced in a blast furnace what does this produce?
Iron
What does molten iron, obtained from a blast furnace, contain?
Approx. 96% iron and 4% impurities l, including carbon phosphorus and silica
Why is iron brittle when obtained from a blast furnace?
It’s impure
How are the atoms in pure iron arranged?
In layers that can slide over one another easily making it soft and malleable
Name some properties of steel depending on the amount of carbon/ other elements.
- Steel with a high carbon content is hard and strong
- Steel with a low carbon content is soft and easily shaped
- Stainless steel contains chromium and nickel and is hard and resistant to corrosion
What is a covalent bond?
A shared pair of electrons between atoms
Where do covalent bonds occur (what type of elements)?
- Non-metallic elements e.g. oxygen
- Compounds of non-metals e.g. sulfur dioxide
Example question:
A chlorine atom has seven electrons in its outer shell. In order to bond with another chlorine atom what occurs?
- An electron from each atom is shared
- This gives each chlorine atom eight electrons in the outer shell
- Each atom now has a complete outer shell
Are covalent bonds strong or weak?
Strong
What do simple molecules contain?
A relatively small number of non-metal atoms joined together by covalent bonds
Why do simple molecular substances (e.g. water) have low melting and boiling points?
There are weak forces of attraction between the molecules which are easily overcome
Do simple molecular substances conduct electricity?
Why?
No, they have no overall electrical charge
Key point:
The intermolecular forces between simple molecules are very weak compared to the strength of covalent bonds in the molecules themselves
How does the size of molecules relate to the strength of the intermolecular forces between simple molecules?
The larger the molecules are the stronger the intermolecular forces between simple molecules become. This means larger molecules have higher melting and boiling points
How does differ in Group 7 of the periodic table?
The molecules get larger as you go down and so the melting and boiling points also increase
What are all the atoms in giant covalent structures linked by?
Strong covalent bonds
What are giant covalent structures?
Solids with very high melting and boiling points
What is diamond?
A form of carbon
Name some features of diamond?
- It has a giant, rigid covalent structure (lattice)
- Each carbon atom forms four strong covalent bonds with other carbon atoms
- All the strong covalent bonds mean that it is a very hard with a very high melting point
- There are no charged particles, so it does not conduct electricity
What is graphite?
A form of carbon
What structure does graphite have?
Giant covalent structure
Does graphite have a high or low melting point?
High
What does each carbon atom form?
Three covalent bonds with other carbon atoms
Describe the structure of graphite.
A layered, hexagonal structure
What are the layers in graphite held together by?
What does this mean?
Weak intermolecular forces.
This means that the layers can slide last each other, making graphite soft and slippery
One electron from each carbon atom in graphite is delocalised. What does this allow graphite to do?
Conduct heat and electricity
Describe the structure of silicon dioxide.
Giant covalent structure and has lattice structure similar to diamond
In silicon dioxide what is each oxygen atom joined too?
Two silicon atoms
In silicon dioxide what is each silicon atom joined too?
Four oxygen atoms
What is graphene?
A form of carbon
A single layer of graphite
How are the atoms in graphene arranged?
In a hexagonal structure, just one atom thick
Name some of graphene’s properties.
V. strong
Good thermal and electrical conductor
Nearly transparent
What is graphene useful for?
In electronics and composite materials
What else can carbon form?
Fullerenes - these contain different numbers of carbon atoms
Describe the structure of fullerenes.
Hexagonal rings of carbon atoms
Describe what buckminsterfullerene is.
-The first fullerene discovered
-Consists of 60 carbon atoms joined together in a series of hexagons and pentagons
What are carbon nanotubes?
Cylindrical fullerenes with very high length diameter ratios
What are sone of the things carbon nanotubes are useful for?
- Nanotechnology
- Electronics
- Reinforcing materials
- To deliver drugs in the body
- As catalysts
What do polymers consist of?
Very large molecules
What are plastics?
Synthetic polymers
What are the atoms within polymers held together by?
Strong covalent bonds
Are the intermolecular forces between large polymer molecules strong or weak?
Strong
What state of matter are polymers at room temperature?
Solids
How is polythene (Poly(ethene)) produced?
When lots of theme molecules are joined together in an addition polymerisation reaction
How many atoms do nanoparticles contain?
A few hundred
