Key concepts in chemistry Flashcards
What is a hazard?
Anything with the potential to cause harm or damage
What is the symbol for oxidising
circle with a flame
What is the symbol for environmental hazard
dead tree and fish
What is the symbol for toxic
skull and crossbones
What is the symbol for harmful
exclamation mark
What is the symbol for highly flammable
line with a flame
What is the symbol for corrosive
test tubes and hand
What is an oxidising hazard
provides oxygen which allows other materials to burn more fiercely eg liquid oxygen
What is an environmental hazard
Harmful to organisms and the environment eg Mercury
What is a toxic hazard
Can cause death by swallowing, inhaling or absorption eh hydrogen cyanide
What is a harmful hazard
Can cause irritation, reddening or blistering of the skin eg bleach
What is a highly flammable hazard
Catches fire easily eg petrol
What is a corrosive hazard
Destroys materials including living tissues eg sulphuric acid
What is a risk assessment
Involves identifying the risks of an experiment and thinking of ways to mitigate them eg protective equipment, low concentrations of substances
what is an atom
a tiny particle of matter made of 3 subatomic particles.
Everything in the universe is made of atoms
What did John Dalton think?
At the start of the 19th century he said atoms were solid spheres and different spheres make up different elements
What did J J Thomson think
His experiments on mass and charge showed atoms were not solid spheres but that atoms contained even smaller negatively charged particles - electrons. He invented the plum pudding model.
What did Ernest Rutherford think
In 1909 they conducted the gold foil experiment. They fired positively charged alpha particles at a very thin sheet of gold. They expected particles to go straight through the sheet but some were deflected alot or came backwards. He said there was a tiny nucleus of positive charge surrounded by a cloud of electrons
What did Niels Bohr think
If electrons floated randomly they would e attracted to the nulceaus and the atom would collapse. He said electrons are in shells around the nucleus and exist in fixed orbits and each shell has a fixed energy. Peer review and other people’s observations supported this
What are the subatomic particles?
Protons - heavy, positive charge
Neutrons - heavy neutral
Electrons - vvv light negative charged
What is the structure of an atom
Protons and neutrons in tiny nucleus in middle of atom (holds almost whole mass of atom). Electrons move around nucleus in shells they are tiny but shells cover alot of space. Size of shells determines size of atom.
Why are atoms neutral
Same number of protons and electrons
Are ions neutral
No they have lost of gained electrons to complete their outer shell and so have positive or negative charge
23
Na which is the mass number
11
23
23
Na which is the atomic number
11
11
What is the mass number
Total number of protons and neutrons
What is the atomic number
How many protons an atom has
How can you work out how many neutrons an atom has?
Subtract atomic number from mass number
What are isotopes
Isotopes are different forms of hte same element.
They have the same number of protons but different numbers of neutrons
What is A with subscript r
Relative atomic mass
What is the relative atomic mass
The average mass of one atom of the element compared to 1/12 the mass of one atom of Carbon-12
Is the relative atomic mass the same as the mass number if there is only one isotope of an element?
Yes
What is isotopic abundance
The amount of each isotope of an element
What is the equation for relative atomic mass
Sum of (isotope abundance x isotope mass number)/ sum of abundances of all the isotopes
Who made the first periodic table
Dmitri Mendeleev
What did Dmitri Mendeleev do
In 1869 arranged the 50 or so known elements into a table of elements
What are the columns in the periodic table?
They are groups
Groups have similar chemical properties
What were the gaps in mendeleevs table?
He arranged elements by atomic mass and fond a pattern emerged. Gaps were for elements that had not been discovered. When they were they had the right properties which supproted his ideas
What are electron shell rules
Electrons occupy shells
They fill lowest energy shells first
Shells have 2,8,8,8 electrons in them
What is the electron configuration of nitrogen
2,5
What is the electron configuration of sodium
2,8,1
What is the electron configuration of carbon
2,4
What does group number tell you
Number of electrons in outer shell
What does the period tell you
Number of shells of electrons
What is an ion
A charged particle
What do all atoms want
A stable electronic structure
ie a full shell of electrons
What is an anion
A negative ion - it has gained electrons
What is a cation
A positive ion it has lost electrons
What does the number of electrons gained or lost equal?
The charge
Which groups are most likely to form ions?
1,2,6,7
Group 1 and 2 are metals they lose electrons to become positive ions
Group 6 and 7 are non metals they gain electrons to become negative ions
What is the overall charge of an ionic compound
Zero
ie the negative ad positive charges balance out
What types of bonds are there
Ionic
Covalent
Metallic
What is an ionic bond
When a metal and on metal react the metal loses electrons to become a positive ion and the non metal gains electrons to become a negative ion. These oppositely charged ions are strongly attracted to each other by electrostatic forces.
What is a dot and cross diagram
Dots and crosses used to show arrangements of electrons in an atom or ion
What is the structure of ionic compounds
Giant ionic lattice structure
Ions packed closely together with very strong electrostatic forces of attraction between oppositely charged ions in all directions
What are the properties of ionic compounds
High melting and boiling point - needs lots of energy to overcome strong forces of attractions
Solids don’t conduct electricity - as ions fixed
As liquids ions can move and carry electric charge
Usually dissolve easily, ions separate and move freely in solution and carry electric charge
What are the advantages and disadvantages of models for structures of substances
2D - Don;t show shape or size
Show what atoms are invovled and how they are connected
Dot and cross show where electrons in bonds came from dont show size or arrangement
3D model show arrangement but only outer layer
Ball and stick - show how atoms connected can visualise structure don;t have correct scale
What is a covalent bond
A strong bond that forms when a pair of electrons is shared between two atoms
What is a simple molecular structure
Simple molecular structures are made up of molecules containing a few atoms joined by covalent bonds
eg H2, HCl, H20,O2, CO2, CH4
What is a double covalent bond
Where two pairs of electrons are shared between two atoms eg like in O2. There are two covalent bonds.
A single covalent bond is sharing a pair of electrons
A double covalent bond is sharing two pairs of electrons
A triple is sharing 3 pairs
How big are simple molecules
10 X 10 to the minus 10 m
What are the properties of simple molecular structures
Atoms within molecules held together by very strong covalent bonds. Forces of attraction between molecules are very weak.
Low melting and boiling points
Usually gases or liquids at room temp
As molecules get bigger strength f intermolecular forces get bigger so melting and boiling points increase.
Don’t conduct electric as no free electrons or ions
Some are soluble, some are not
What are polymers?
Molecules made from long chains of covalently bonded carbon atoms.
Formed when lots of small molecules (monomers) join together.
An example is poly(ethene)
What are giant covalent structures
All the atoms are bonded to each other by string covalent bonds
High melting and boiling points
Don’t conduct electricity
Insoluble in water
List the Carbon based giant covalent structures
Diamond
Graphite
Graphene
What are the properties of diamond and why
A network of carbon atoms that all form 4 covalent bonds.
Held in lattice structure so very hard, used as cutting tools
High melting point
Do not conduct electricity
What are the properties of graphite and why
Each carbon forms 3 covalent bonds making sheets of hexagons
Layers held together by weak bonds so they easily move over each other.
Slippery and soft used as lubricant
High melting point due to 3 strong covalent bonds
Conduct electricity as one delocalised electron - used for electrodes
What are the properties of graphene
Single layer of graphite
One atom thick so 2D structure
What are fullerenes
Molecules of carbon shaped as tubes, balls
Made of carbon atoms in pentagons, hexagons and heptagons
Can be used as a cage around other molecules used to deliver drugs to body
Have huge surface area so make great industrial catalysts
What are nanotubes
These are fullerenes.
Tiny cylinders of graphene so conduct electricity
High tensile strength
Add strength without weight eg tennis rackets
True or false metallic bonding involves delocalised electrons
True
True or false metals consist of small structures
False they consist of a giant structure
Explain metallic bonding
Found in metallic elements and alloys.
Electrons in outer shell of metal atoms are delocalised. Strong forces of electrostatic attraction between positive metal ions and shared negative electrons.
Forces hold atoms in a regular structure known as metallic bonding
Very strong
What are the physical properties of metals
High melting and boiling point as strong forces
Shiny solids at room temperature
Insoluble in water
More dense than non metals as ions packed tight together
Malleable as layers can slide over each other so can be hammered or rolled into sheets
Good conductors of electricity and heat due to delocalised electrons
True or false metals and non metals have the same physical properties
False
All metals have metallic bonding so similar properties
Non metals don’t have metallic bonding and have a range of structures so wide range or properties
Non metals tend to be dull, lower boiling point, low density, don’t conduct electricity
True or false metals and non metals have different chemical properties
True
Metals tend to lose electrons whilst non metals tend to gain them.
metals on left of periodic table, non metals on right
