2.1 Flashcards
What is an element?
Same atoms
What is a compound?
Different atoms chemically bonded
How do you split a compound ?
Chemical reaction
What is in a mixture?
Different elements or compounds not chemically combined
How do you separate a mixture?
Physical techniques
What physical techniques can separate mixtures?
Filtration
Distillation
Crystallisation
What is a molecule?
Any of the same elements chemically joined
Why is found in the nucleus of an atom?
Protons
Neutrons
Where are the electrons found in the atomic structure ?
Shells
What is the charge of an atom?
0
Why is there no overall charge of atoms?
Electrons are cancelled out by protons
On the periodic table which number is the atomic number?
Smaller number
What is the atomic number
Number of protons
Where is the mass number on the periodic table?
Biggest number
What is the mass number?
Total of protons and neutrons in the nucleus
How do you calculate number of neutrons ?
Mass number - atomic number
Why do elements react?
Full outer shell
What are boiling points of ionic compounds? Why?
Very high
Electrostatic forces require lots of heat energy to break
Can ionic compounds conduct electricity ? Why?
No
Ions cannot move because of the electrostatic forces of attraction.
When can ionic compounds conduct electricity? Why?
Molten or dissolved in water
Breaks electrostatic forces
Ions can now move and carry current
Why does ionic bonding contain?
Transfer of electrons of non metals and metals
What does covalent bonding contain?
Shared electrons of non metals
What are the properties of simple covalent molecules?
Low melting and boiling points
Usually gases or liquids at room temp
Do not conduct electricity
What holds the atoms in each covalent molecule together?
Strong covalent bonds
What holds the molecules together in a covalent molecule?
Weak intermolecular forces
Why does it not take much energy to turn a simple covalent molecule into a gas?
Weak intermolecular forces are easily broken with little energy
Why do simple covalent molecules not conduct electricity?
They do not have an overall electric charge
What are the 4 giant covalent molecules?
Diamond
Graphite
Fullerenes
Silicon dioxide
What is diamond made of and how are these atoms bonded?
Carbon atoms with 4 covalent bonds to other carbon atoms
What are the properties of diamond and why do these occur?
Extremely hard
Very high melting point
Because of the large number of strong covalent bonds
What is graphite made of and how are the atoms bonded?
Carbon atoms with 3 covalent bonds
Why is graphite very soft?
It has layers which are not strongly held together as there aren’t covalent bonds between layers - only weak intermolecular forces
Layers can then slide over each other
Why can graphite conduct electricity and heat?
Each atom has a spare electron due to only having 3 covalent bonds.
The delocalised electrons can move and conduct electricity and heat.
What can fullerenes be used for?
Drug delivery into the body
Lubricants
Catalysts
Nanotubes for reinforcing materials e.g. Tennis rackets
How are fullerenes structured?
Hexagonal rings of carbon
What elements does silicon dioxide contain?
Oxygen and silicon
Why does silicon dioxide have a high melting point?
Contains a large number of covalent bonds
What are the forces between oppositely charged ions called?
Strong electrostatic forces
Why can metals conduct heat and electricity?
Because of their delocalised electrons
Why can metals be bent and shaped?
The layers of atoms slide over each other
What are alloys?
2 or more different metals
Why are alloys harder than pure metals?
Different story sized atoms of metals distort the layers in the structure, making it more difficult for layers to slide over each other
What do shape memory alloys do?
Give an example.
Return to their original shape
Nitinol is used in dental braces