Section 10: Key Concepts In Chemistry Flashcards
Hazard symbols
- Hazard
- Oxidising
- Toxic
- Environmental Hazard
- Corrosive
- Highly flammable
Oxidising
Provides oxygen which allows materials to burn fiercely
- liquid oxygen
Hazard
Can cause irritation, bleeding, blistering of the skin
- Bleach
Environmental hazard
Harmful to organisms and to the environment
- Mercury
Highly flammable
Catches fire easily
- Petrol
Toxic
Can cause death by swallowing, breathing in, absorption through the skin
- hydrogen cyanide
Corrosive
Destroys materials including living tissues - skin
- concentrated sulfuric acid
Plum pudding model
Positively charged atoms were spread across and electrons were scattered across the atom
Rutherfords atom
- Electrons were in empty space
- Protons are in the nucleus of the atom
- Most of the atom has empty space
- Doesn’t explain emission and energy transfer
Bohrs model
- Electrons only exist in fixed orbits or shells and not anywhere in between.
- Each shell has a fixed energy
- supported by many experiments
What 3 subatomic particles are atoms made up of
- Protons
- Neutrons
- Electrons
Protons
- Heavy
- Positively charged
- Relative mass = 1
- Relative Charge = +1
Neutrons
- Heavy
- Neutral
- Relative mass = 1
- Relative charge = 0
Electrons
- Hardly any mass
- Negatively charged
- Relative mass = 0.0005
- Relative charge = -1
Radius of an atom
- Known as atomic radius = 10^-10m
How to find the number of protons
Number of protons = number of electrons
Atomic number tells us how many protons
Why are atoms neutral
They have the same number of protons as electrons
How to find the number of neutrons
Mass number - atomic number
Where is the mass number
It is the biggest number - usually the top of the element
What does the mass number tell us
The total number of protons and neutrons
What does the atomic number show
The number of protons
What are isotopes
Different forms of the same element. They have the same number of protons but different number of neutrons.
They have the same atomic number but different mass numbers
How to work out the relative atomic mass
- if an element has one isotope, the relative atomic mass will be the same as its mass number
- from the isotopic abundance
How to work out isotopic abundance
(Mass number of isotope 1 X isotope abundance 1) + (mass number of isotope 2 X isotope abundance 2)/the sum of abundance
If the abundance is given in percentages, divide by 100
What is the relative atomic mass
Average mass of atoms of an element
Definition of ionic bonding
The transfer of electrons
When a metal and a non metal react together. The metal atom loses an electron to form a positive ion and the non metal gains an electron to form a positive ion. These oppositely charged ions are attracted to each other by electrostatic forces called ionic bonds.
How do you show how ionic compounds are formed
You use the dot and cross diagram to show the arrangements of electrons in an atom or ion. Each electron is represented by a dot or a cross so they can show which atoms the electron in an ion originally came from
Ionic compounds
Ionic compounds always have giant ionic lattice structures. These ions form a closely packed regular lattice. They have strong electrostatic forces of attraction between the oppositely charged ions in all directions.
Properties of ionic lattice structures
- High melting and boiling points. This is because of the strong attraction between the ions so it takes a lot of energy to over come the strong electrostatic forces
- Doesn’t conduct electricity. This is because all the ions are in fixed places and cannot move meaning they don’t carry an electric charge because no electron has been delocalised.
- when it melts the ions are able to move and will carry an electric charge.
- Dissolve easily in water. The ions separate and are free to move so they will carry an electric charge
Models that show structures
- 2D representations
- Dot and cross diagrams
- 3D molecules
- Ball and stick diagrams
Advantages of 2D representation
- simple and great at showing what atoms something contains and how the atoms are connected
Disadvantages of 2D representations 
Doesn’t show the shape of the substances and they don’t give you an idea about the size of the atom
Advantages of dot and cross diagrams
Useful for showing how compounds or molecules are formed and where the electron in the bonds or ions came from
Disadvantages of dot and cross diagrams
They don’t usually show you anything about the size of the atom, ion or how they’re arranged
Advantages of 3D models
Show the arrangement of ions
Disadvantages of 3D models
Only show the outer layer of the substance
Ball stick models
Show how the atoms in a substance are connected, you can draw them or make the with plastic molecular kits or as computer models
Advantages of ball stick models
- They’re great for helping to visualise structures as a show the shape of the lattices or molecules in 3D.
- They’re more realistic than 2D drawings
Disadvantages of ball stick models
- They’re a bit misleading as they make it look like there are big gaps between atoms, where in reality this is where the electron clouds interact
- they don’t show the correct scales of the atoms or the ions. The atoms and ions are really different sizes but this isn’t shown well
Covalent bonding
A strong bond that forms when a pair of electrons is shared between the 2 atoms
Simple molecular substances
Made up of molecules containing a few atoms joined by covalent bonds
Properties of simple molecular substances
- atoms within the molecules are held together by very strong covalent bonds so the forces of attraction between those molecules are very weak
- The melting and boiling points are very low- to melt or boil, you need to break the ‘feeble intermolecular forces’ and not the covalent bonds
- they are gases and liquids at room temperature
- as molecules get bigger, the strength of the intermolecular forces increases. This means more energy is needed to break them apart so the melting and boiling points increase.
- they don’t conduct electricity- they don’t have any free electrons or ions
- some are soluble and some aren’t
Polymers
- they are made up of long chains of covalently bonded carbon atoms- example of this would be polythene
- they are formed when lots of small molecules called monomers join together
Properties of giant covalent bonds
- All the atoms are bonded to each other by string covalent bonds
- Very high melting and boiling points as you need a lot of energy to break apart the covalent bonds
- Don’t conduct electricity because they don’t have any charged particles (except for graphene and graphite)
- Aren’t soluble in water
Which giant covalent structures conduct electricity and why
Graphene and graphite
They both have charged particles
Diamond
- Made up of a network of carbon atoms that each form for covalent bonds
- strong covalent bonds take a lot of energy to break so diamond have a high melting point
- They are really hard- strong covalent bonds also holds the atoms in rigid lattice structure
- doesn’t conduct electricity as there isn’t any free electrons or ions
What are diamonds used for
Strengthen cutting tools
Graphite
- Each carbon atom only forms 3 covalent bonds creating sheets of carbon atoms arranged in hexagons
- No covalent bonds between the layers so they’re only held weakly so they’re free to move over each other
- makes graphite soft and slippery so it is a lubricating material
- High melting point - covalent bonds between the layers need loads of energy to break apart
- Can conduct electricity - only 3 out of 4 carbons outer layer electron is used in bonds so only 1 electron is delocalised and can move
What can graphite be used
As a lubricating material - no covalent bonds so the layers are held very weakly and they’re free to move over each other
Graphene
- type of fullerenes
- one layer of graphite
- a sheet of carbon atom joined together in hexagons
- 1 atom thick making it a 2D substance
What can you tell about the structure of the atom from the proton number
The proton tells you the number of protons in the nucleus, but for a neutral atom it tells you the number of electrons
Why are the relative atomic mass of elements rarely have whole numbers
The relative atomic mass is the average mass of an atom which includes the diffferent isotopes and their natural abundance. The averages aren’t whole numbers
How did Mendeleev arrange the periodic table
By mass
Why does oxygen have a low boiling point
Weak forces of attraction between the oxygen molecules
What is a covalent bond
When a strong bond forms when a pair of electrons are shared between 2 atoms
Why is chlorine a gas rather than a liquid at room temperature
Chorine has covalent bonds between the atoms which form simple molecules. There are weak forces of attractions between the molecules to little energy is needed to break these forces of attraction so chlorine has a low boiling point
Fullerenes
- form spheres and tubes
- molecules of carbon shaped like closed tubes or hollow balls
What are fullerenes made up of
Carbon atoms arranged in hexagons but can also contain pentagons and heptagons
What are fullerenes used for
- form spheres or tubes
- used to cage other molecules. The fullerene structure forms around another atom of molecule which is then trapped inside. This could be used to deliver a drug directly into the body
- catalyst
How do we use fullerenes to deliver drugs directly into your cells
They cage other molecules. The structure forms around another atom or molecule which is then trapped inside.
How is fullerenes used as a catalyst
They have a huge surface area so they can help make great industrial catalysts as the individual catalyst can attach to the fullerenes (the bigger the surface area the better)
Nanotubes
Are also fullerenes that strength materials without adding much weight
Why are nanotubes used to strengthen materials
Nanotubes have a high tensile strength so they can be used to strengthen materials without adding much weight
What does tensile strength mean
They don’t break when stretched
Properties of nanotubes
- conducts electricity- tiny cylinders of graphene as it has a delocalised electron
What makes metals thick
Metallic bonding
How does metallic bonding work
- Metals consists of a giant structure
- The electrons in the outer shell of the metal atoms are delocalised. There are strong forces of electrostatic forces between the positive metal ions and the shared negative electrons.
- These forces of attraction hold the atoms together in a regular structure also known as metallic bonding which is very strong
- Compounds that are held together by metallic bonding include elements and alloys
What produces all the properties of metals
The delocalised electron
Physical properties of metals
- Most compounds with metallic bonds have a high melting and boiling point as the electrostatic forces between the metal ions and the delocalised sea of electrons are very strong and need a lot of energy to break the forces.
- Shiny solids at room temperature as they have a high melting and boiling point
- Aren’t soluble in water
- Metals are more dense than non-metals as the ions in the metallic structure are all packed close together
- Pure metals have layers of atoms which can slide over each other, making metals malleable
- The delocalised electrons carry electrical charge and thermal energy through the material so metals are good conductors of electricity and heat
Physical features of non metals
- form of different structures so they have a wide range of chemical and physical properties
1. Dull looking, more brittle and have lower boiling points.
2. Not a solid at room temperature bc they have low boiling and melting points
3. Don’t conduct electricity
4. Low density
Chemical properties of metals
- Lose electrons to gain full outer shells.
- Found at the bottom left hand side of the periodic table
- outershells are usually under half full
Chemical properties of non metals
- gain electrons to form a full outer shell
- at the top right hand side of the periodic table
- outershell usually over half full
What happens during a chemical reaction
No atoms are destroyed snd no atoms are created, this means that there are the same number and types of atoms on either side of a reaction equation. You can see this reaction in a closed system as the total mass of the system before and after doesn’t change.
Precipitation reaction
When 2 solutions react and an insoluble solid called a precipitate forms in the solution
How do you know if there is a gas involved in a reaction
If the mass seems to change
What does it mean if the mass increases
It means that at least one of the reactants is a gas found in air and the products are solids, liquids or aqueous.
1. Before the reaction, gas is floating around in the air but it’s not contained in the reaction vessel so you can’t measure it’s mass.
2. When the gas reacts to form part of the product it becomes contained in the reaction vessel this makes the total mass inside of the vessel increase as it contains gas.
What does it mean if the mass decreases
Because some or all of the reactants are solids, liquids or aqueous and at least one of the products is a gas.
1. Before the reaction, solid, liquid or aqueous reactions are contained in the reaction vessel.
2. If the vessel isn’t closed then some of the gas can escape from the reaction vessel as it’s formed so its no longer contained in the reaction vessel and you can’t measure its mass.
3. This makes the total mass of the stuff inside of the reaction vessel decrease.
How to work out relative formula mass
The relative atomic mass multiplied by the number of atoms it has and add them all together
How to work out the percentage mass of an element in a compound
The ar of an element x the number of atoms divided by the mr of the whole compound multiplied by 100
Precipation reaction
A substance that ‘crashes’ out of solutions to form a solid
