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
Metallic bonding
A regular structure of positive metal ions in a sea of delocalised electrons. There are strong forces of electrostatic attraction between the positive metal ions and the shared negative electrons. V strong!!
Compounds held together by metallic bonding
Metals and alloys
Properties of metals
High melting and boiling points (strong electrostatic attractions that require much energy to break).
Shiny solids at room temp (generally)
Insoluble
Dense
Malleable (as layers of atoms can slide over each other)
Conductors of electricity and heat (delocalised electrons are free to carry thermal energy and heat)
Who created the periodic table and when?
How many elements did they sort?
Dmitri Mendeleev sorted 50 elements in 1869
How did Mendeleev sort the table?
By order of increasing atomic mass.
Placed similar chemical properties in columns.
Why were there gaps left over in Mendeleev’s table?
Because of isotopes.
Also meant that we could predict properties of undiscovered elements.
How many elements are there now
100
How are modern periodic tables ordered?
According to increasing atomic number.
What does a group tell you?
Properties/ number of electrons in outer-shell.
What do periods tell you?
Number of electron shells
Where’s the partition between metals and non metals on the periodic table?
Boron to astatine staircase
What’s on the left of the periodic staircase?
Metals
Ammonia chemical formula
NH3
Ions for: Ammonium Nitrate Sulfate Hydroxide Carbonate
NH4+ NO3- SO42- OH- CO32-
Oxidising
Allows other materials to burn much quicker
E.g Liquid oxygen
Harmful
Causes irritation, reddening/blistering of skin
E.g. bleach
Environmental hazard
Harmful to organisms and environment
Highly flammable
Catches fire easily
Toxic
Can cause death by e.g. swallowing, reading in, absorption through skin
Corrosive
Destroys materials, including living tissue
Average size of an atom
100 picometers
Proton
Positive nucleon w mass of 1
Neutron
Neutral nucleon with mass of one
Electron
Negative subatomic particle situated on shell of an atom with relative mass of 1/2000
Nucleons
Subatomic particle is situated in the nucleus of an atom
Mass number
Number of protons and neutrons
Atomic number
Number of protons
How is an atom neutral?
The number of electrons always equals the same number of protons. Electrons have a relative charge of negative one and protons have a relative charge of positive one, therefore they always cancel each other out.
What happens if they are an unequal number of electrons to protons?
Atom becomes charged and is an ion
Isotope
Atomic forms of the same element which have the same proton number but different mass number due to having a different number of neutrons in the atom.
Relative atomic mass
The weighted mean mass of an atom.
Is rounded to the nearest 0.5 in Periodic Table.
Relative abundance
Amounts of each isotope in relation to total amount of element in the world
First atomic model theory
Daltons billiard ball 1800s
Theory of all matter is made out of atoms that can’t be broken down, different elements are different atoms which are rearranged in chemical reactions
Second atomic model
JJ Thompson’s plum pudding model 1900s
Demonstrated negative subatomic particles within the atoms floating around randomly
Third atomic model
Rutherford nuclear atom 1900
Demonstrated nucleus within the atom
Fourth atomic model
Bohr
Demonstrated electron orbit with neutrons and free space within atom
Who carried out the gold foil experiment
Rutherford’s assistants, Geiger and Marsden 1911
What did the gold foil experiment compose of?
A vacuum with alpha radiation, a piece of gold foil and a detector
Why was the gold foil experiment carried out in a vacuum?
So the air particles wouldn’t get in the way
What occurred during geiger and Marsden’s experiment?
A beam of alpha particles was aimed at gold foil and their passage through was detected. Some atoms were reflected, others deflected, most just passed straight through. This supports Rutherford atomic model
Which particles repel
Positive and positive
What did the gold foil experiment show
Particles passing straight through demonstrated the much free space on the atom.
Particles reflected demonstrated the nucleus with a positive charge.
Particles deflected demonstrated a large nucleus.
Which energy levels are field first?
The lowest
2 8 8 2
What happens when atoms have full electron shells?
More stable, less reactive
Relative formula mass
Relative atomic masses of all atoms within a compound added together.
How do you find the relative formula mass of a compound?
Find relatively Tomich masses of each element on the periodic table and multiplied by the amount of atoms of the element in a compound. Add the total of relative atomic masses.
Empirical formula
The smallest whole number ratio of atoms within the compound.
How can you find the molecular mass of a compound with its empirical formula?
Find the relative masses of each element.
Divide the relative mass by the relative mass of the empirical formula.
Avogadro’s constant
6.02×10 to the 23
Mole
6.02×10 to the 23 particles of an element.
Is equal to Relative particle mass for that element.
Number of moles
Mass (g) / relative mass
What’s concentration measured in
Grams per decimetre cubed
Concentration formula
Mass of solute / volume of solution
How to work out in Perico formulas from masses of the elements
Work out how many moles of each element you have (divide by RAM)
Find smallest whole number ratio
Limiting reactant
The reacting that has been used up in a reaction, causing the reaction to stop.
What is the relationship between amount of product formed and amount of limiting reactant used? why?
Amount of product formed is directly proportional to the amount of limiting reactant used, as more limiting reactant will mean more reactant particles can take part in the reaction and produce more product.
How do you work out the mass of product formed from a given mass of the limiting reactant?
Workout relative formula masses of reactants and products.
Calculate the number of moles in the substance you know the mass of.
Use equation to work out how many moles there will be a bit of other substance.
Calculate mass
How can you balance equations using reacting masses
Divide mass of each substance by relative formula mass to find moles.
Divide number of moles by smallest number of moles in reaction.
