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Chem Paper 1 - Atomic Structure and the periodic table (Group 1: Alkali…
Chem Paper 1 - Atomic Structure and the periodic table
Elements In The periodic Table
A Diagram made up from about 100 chemicals
The chemicals are called elements
All substances are made from these elements
an "Element" Is a substance made up from only one type of atom
All individual particules that make up a substance are all the same
An "Atom" is the simplest particles that a substance can be broken down into (Gold Cutting Ananolgy)
Metals = Left hand side
Non-Metals = Right Hand Side
Metals and non metals are divided on the periodic table by a staircase shape
Groups are categorizes where elements are put together because they reactivity is similar
Group 1 = Alkali Metals (Lithium, Sodium, Potassium, Rhubidium, Cesium)
Middle Sector = Transition Metals (Has many elements but some popular are: Iron, Copper Gold, Silver, Zinc)
Group 7 = Halogens (Florine, Chlorine, Bromine, Iodine)
Group 0 = Noble Gases, least reactive elements (Helium Neon, Argon)
Discovery Of The Structure Of The atom
John Dalton (1766 - 1844)
All Matter Is Made Of Atoms
All Atoms Are Indivisible and Indestructible
All Atoms of a given element are identical in mass and properies
Compounds are made up from 2 or more different atoms
a Chemical Reaction is a rearrangement of atoms
(Not all his rules were quite correct but they led to help other future scientists explore and refine theory)
J.J. Thomson (1856 - 1940)
Discovered existence of electrons
Atoms were made of smaller particles and were common to all atoms
He suggested these "Subatomic" particles where evenly distributed in the atom
His ideas then became the Plum Pudding Model
Ernest Rutherford (1871 - 1937)
He Disproved the Plum Pudding Model
Most of the mass of an atom is concentrated in the centre
Planetary Model - Protons in the center of the nucleus and the electrons orbit around it
Niels Bohr (1885 - 1962)
Electrons occupy separate orbitals or shells
He adapted Rutherfords model
Atomic Structure
Symbols
O is a symbol of Oxygen
O2 Represents two oxygen atoms joined together
Na is the symbol for sodium
2Na is the symbol for two sodium atoms but these are not joined together
Atoms
The smallest particle that can exist
Still behaves as that element (Cutting Gold Analogy)
Atoms are extremely small
Atoms have a radius of 0.0000000001 M
The radius is written as "1 x 10^-10"
Atoms weigh about 0.00000000000000000000001 g
The Weight is written as "1 x 10^-23"
Atoms Are made up of even smaller particles called Sub Atomic Particles
Subatomic Particles
Different numbers that make elements distinct from one another
Protons
Determines what element the atom is
Each element has a Unique number of protons
Different Number of Protons = Different element
Positive Charge
Relative Mass = 1
Neutrons
Approx. Same size as protons
No Charge
Relative Mass = 1
Electrons
Much smaller than protons and neutrons
Relative mass = 0.0005
Negative Charge
They have Particular places in the atom
Protons and Neutrons are found in the center of the atom in the nucleus
Electrons orbit around the nucleus
Nucleus contains almost all of the mass of the atom
But the nucleus is small compared to the overall size of the atom
Electrons are widely spaced as they orbit the nucleus
Much of the atom is empty space
Protons and electrons have opposite charges
Because protons and electrons have opposite charges, they are attracted to each other
The Protons and Electrons being attracted is what keeps the electrons in orbit around the nucleus
Atoms have no overall charge
Atoms have no overall charge because an atom always have an Equal number of Protons and Electrons so they cancel each other out to be neutral (and a neutron already is neutral)
Subatomic Particles
Protons
Number of protons determines what the element is
Smaller number is the atomic number which is also the proton number
For example: Sodium Will Always Have 11 protons
If an atom had an addition atom it would not longer be Sodium
To keep atoms neutral they need to have the same number of protons and electrons
Mostly all of the mass comes from the nucleus (Protons and Neutrons)
Relative Mass = 1
Neutron
The Mass number is the sum of Protons and Neutrons
So to find the number of neutrons Mass Number - Atomic Number
Sodium has an atomic mass of 23 and the atomic number is 11 so to find the amount of neutrons is 23 - 11, so 12 neutrons
Electrons
Such a tiny mass it doesnt really add to the mass of the atom
Same number of protons
To Keep atoms neutral they need to have the same number of protons and electrons
Electronic Structure
Electrons
Smallest of the subatomic particles
Almost no mass
Negative Charge
They are found around the central nucleus
Electrons move around the nucleus similar to how planets orbit the sub
Electrons are held in place to the attraction to positively charged protons
Atoms have different numbers of electrons
Atomic Number = Electron Number
Organised into energy levels which are called shells
Each shell can hold a particular number of electons
Only when one shell is full can electrons enter the next shell
Electrons fill shells in particular ways
Lowest energy level is found closest to the nucleus
The shells then fill up gradually moving further away from the nucleus bases on their energy levels
First shell can hold 2 electrons
The rest of the shells can hold 8
Electron configuration
Sodium for example: 1st shell has 2, 2nd shell has 8, 3rd shell has 1
Can be represented like this [2,8,1]
can also be represented by a diagram
Determines many chemical characteristics of the element
Having a full outer shell makes a Very Stable Atom
So Noble Gases are very stable atoms
Alkali Metals have some of the most reactive elements because they have the most incomplete outer shell (1 electron)
Electrons are in groups bases on the number of electrons in there outer shell which affects there reactivity, so there group number is how many electrons there are on their outershell
Rows on periodic table
Rows are called periods
As you move across any period, the number of electrons increases
For example: Period 2, begins with Lithium, ALL the elements in this period has 2 shells of electrons that is why it is the seconds period
Each succesive element has 1 more electron than the previous
Combining Elements
An elements is a substance made up from one type of atom
When chemical reactions occur then atoms can join together to become compounds
Compound
A Substance made from atoms of 2 or more elements that are chemically combined together
Can't be separated by physical methods (Filtering for example)
Ionic Bonds
When a metal and a non metal combine
Transfer of electrons from metal to non-metal
After ionic bonding the atoms become oppositely charged
Metal is positively charged and the non metal is negatively charged
Covalent Bonding
When a Non Metal and a Non Metal combine
The atoms share the electrons
when atoms share electrons their held together in pairs or small groups known as molecules
When elements come together to form a compound, they are completely changes
A Compound is a new substance with completely different properties
Water is a compound made from the elements Hydrogen and Oxygen (H2O)
Hydrogen and Oxygen are both highly reactive, And Hydrogen gas is extremely flammable
So in contrast to Hydrogen being flamable and both of them being reactive, Water is a liquid at room temp. Relatively unreactive and can be used to actually put out fires not set them
It is very difficult to get H2O back to Hydrogen and Oxygen
Mixtures
Easy to separate unlike compounds
A Substance made from atoms of 2 or elements that are NOT chemically combined
Representing Chemical Reactions
A Balanced Equation is an equation with the same number of atoms of each type on both sides of the equation
Balanced Equations are neccesary as atoms are only rearraganged in a chemical reaction.
You cant lose or crease new atoms in a chemical reaction
Balancing a symbol equation
Need to know all the chemicals that the reaction starts with (This is called the reactants)
Need to know the chemicals produced in the reaction (These are called the Products)
E.G. Copper Oxide + Hydrochloric Acid --> Copper chloride + Water
Isotopes and Relative Atomic Mass
Element (A substance that consists only of one type of atom)
BUT There are slight differences between atoms of most elements, These are called isotopes
Isotopes are Atoms with the same number of protons and electrons as one another but different number of neutrons
Isotopes behave chemically in the same way because chemical reactions are determined by number of electrons
Isotopes have different masses due to a different number of neutrons
Physical properties such as density will be slightly different
Example: Chlorine has two isotopes ^35Cl and ^37Cl, Those numbers refer to the mass numbers of each isotope, Clorine 37 would be heavier because it has more neutrons in its nucleus
When thinking about chemical reactions it doesn't matter what isotope we have
Elements exist as mixtures of isotopes
If there was a flask with chlorine gas, it would naturally have a mixture of Chlorine 35 and Chlorine 37
Relative atomic mass is an average of all isotopes
It being an average is why when looking at a periodic table not all of the atomic masses are whole numbers
Calculating Relative Atomic Mass
Need to know the mass number of each isotope and the relative abundance
The relative abundance is the percentage of element that exists as an isotope
For Chlorine 75% are Chlorine 35 and only 25% are chlorine 37
So the calculation would be:
Separation methods
Chemical Synthesis
uses reactions to produce a desired substance
Chemical reactions are usually straight foward, all we need to do is mix substances with the correct quantities with suitable temperature & pressure
The Hardest part when the Reaction is finished and we need to separate the product from the mixture
Most chemical reactions take place in solution so involve liquids
Separating funnel
useful in separating immiscible liquids
Made of glass
Bulges in the middle
Allows for the liquids to be shaken together
Allowing dissolved substances so move into their correct layers
Tap at the bottom
When left liquids separate into 2 layers
Opening the tap allows it to only let out the bottom layer of liquid
Immiscible liquids are liquids that don't mix
When liquids don't mix they from 2 distinct layers
Miscible liquids are liquids that do mix. Cant be separated by a separating funnel
Crude Oil and Liquid air are examples of miscible liqiuds
Fractional Distillation is the normal way of separating miscible liquids
Fractional distillation separates components of mixture into franctions
Fractional Distilation
Air is cooled to -200 C
So all gases condense into a liuid except water and carbon dioxide so they can freeze and be easily removed
Different substances have different boiling points
with the different substances having different boiling points we can separate them bu gradually increasing the temperature so that each substance will boil individually while the others remain liquid
The gas given off can then be isolated from the mixture
This is done by using a franctionating column. This column is warmer at the bottom than it is at the top
the gas with the highest boiling point will go all the way to the top and if oxygen boils it will condense back to a liquid where it is cooler
One by one these gases are separated by different columns each times
Crude oil is the main thing distilated this way
Elements & Compounds
Atoms are the smallest particle that can exist on its only, Only some substances exist as single atoms
Elements are made up of only one type of atom
there are 118 elements (Periodic Table)
Gold is an element and is only made up of gold atoms (Gold Cutting Ananolgy)
Gold used for jewelerry is normally mixed with other metals so its not as soft and doesn't get scratches on it as easy
A mixture of different metals is called an Alloy
Group 0 = Noble Gases (Their Gases Which are made up of single atoms)
Oxygen being in the periodic table means it is an element
However it is not made up of individual oxygen atoms but Oxygen molecules
A Molecule is a group of atoms chemically bonded together
Oxygen molecules contain 2 oxygen atoms
this is why it's chemical formula is O2
It shows two oxygen atoms joined together with a covalent bond
Oxygen is a Diatomic Molecule (Di meaning 2)
Oxygen is still an element because it still only contains oxygen atoms but are found it pairs
An oxygen atom can also exist in a three in that cause it is called an ozone
Other Diatomic molecules are: Hydrogen, Nitrogen, Chlorine, Bromine
Some elements are made up of Molecules with many atoms, These are known as Giant Covalent Structures
Giant Covalent structures include Carbon and sulphur
Carbon atoms exist in different forms/ Allotropes such as diamond or graphite because they both contains carbon atoms bonded together in a giant structure
H2O shows that two hydrogen atoms are bonded to one Oxygen atom
(Water is a compound)
A Compound is a substance that contains atoms of 2 or more different elements chemically bonded together
Compounds may be covalent (Atoms are all non metals)
Or ionic (Atoms are metals and non metals)
There are many different compounds, One of the most common ones being Salt which is Sodium and Chlorine
Sodium is a very reactive metal and also a toxic gase
Chlorine is a toxic gas
But both together they make a crystalissed solid that you can eat without no dire consequences
Which shows properties of a compound can be very different
Mixtures
Mixtures are two or elements combined but not chemically
Air is a mixture of different elements including oxygen, nitrogen and argon, along with some compounds like carbon dioxide and water.
Tap water water contains water molecules along with dissolved ions.
These components are separated using physical methods
Distillation for example. Distillation can make tap water into pure water
Group 1: Alkali metals
Found in the first collumn
Contains: Lithium, Sodium, Potassium, Rubidium, Cesium, Francium
These elements are amongst the most reactive
They are metals and have common properties to other metals
Good thermal Conductors
Good electrical conductors
Shiny and silvery but because they are highly reactive the silvery look quickly tarnishes when exposed to air
Reaction with air is an oxidation reaction
Alkali metals are stored under oil to prevent oxidation (oil stops contact with air)
Alkali metals burn in air
When metal atoms react with other elements to form compound they give away there negative particles(electrons) and form ions (positively charged) (This is ionic bonding)
All alkali metals react in the same way to form ions
They all form ions with a single positive charge
This is because they only have 1 electron to give away (Group 1)
Sodium Atom --> Sodium ion + Electron
Na --> Na+ + e-
This shows us a sodium atom loses an electron
This is an oxidation reaction because sodium is losing electrons
We can see that electrons are being lost because it says "e-"
Sodium Chloride is salt. Sodium reacts very vigirously with chlorine when the reaction takes place, releasing alot of energy
For example, Sodium chloride is white and dissolves in water to give a colorlessness solution
Alkali metlas are different from metals because they are not strong or hard wearing infact they are so soft they can be cut with a knife
Lithium is the hardest metal in the group but can still be cut
Sodium is easier to cut and has the consistency of cheese
The further down the group you go the softer the metals become
Alkali metals have quite low melting points
Lithium has the highest melting point (180 C )
Cesium's melting point is so low, the heat produced by your hand is enough to melt it into a liquid
All have low density so they are all fairly light for their size
The first three elements are light enough to float in water
They have no use in construction as they are so weak
Sodium is used in streetlamps to give it their yellow glow
Sodium is also a coolant in some nucleur reactors
Reactivity in Group 1
Lithium with water
Fizzes and produces bubbles of a gas
If this gas is collected if tested in a boiling tube then it will burn rapidly and a squeaky pop will be heard
This squeaky pop tells us that the gas is hydrogen
Sodium With Water
Produces Hydrogen quicker than lithium
Energy is sufficient to melt the sodium
So a ball of Molten Sodium is seen on the surface of the water
Adding universal indicator to the water will make it turn purple to show that an alkali has been produced
This produces Sodium Hydroxide
Sodium + Water --> Sodium Hydroxide + Hydrogen
All reactions with water for hydrogen gas and alkali metal
Potassium With Water
Hydrogen spontaneously ignites
Rubidium With Water
Firework show shooting sparks
Cesium With Water
Violently explosive that he glass with water is completely shattered
Safety with reacting group 1 metals
Lithium, Sodium and Potassium is safe enough to be done in a school but a safety screen may be necessary
All three of these would be stored under oil to prevent reaction with oxygen and water
Rubidium and Cesium are too dangerous to be found in a school so more safety measures are needed to be put into place
As you move down the group the reactivity increases
Least reactive is Lithium
Cesium is highly reactive
This is to do with the relative size of the atom
Lithium has small atoms with a few electrons making it the least reactive (the electron in the outer shell is close to nucleus)
As moving down the group atoms get larger with an extra shell of electrons so the outer shell will be further away from the nucleus
Group 1 metals react readily with the group 7 (The halogens)
e.g. Sodium reacts with Chlorine to make Sodium Chlorine
Group 7 - Halogens
Contains: Florine, Chlorine, Bromine, Iodine (There is Astatine but it is radioactive and not stable enough to be studied easily)
All the halogens look very different
Darker in colour as moving down the group
Florine and Chlorine are gasses, Bromine is a liquid and Iodine is a solid so this represents an increase in melting and boiling points going down the group
Halogens need to be handled carfully as they are a dangerous group of chemicals
Chlorine gas is highly Toxic and should only be handled in a fume cupboard
Bromine Liquid is both Toxic and Corrosive so should be handled wearing gloves and in a fume cupboard
Unlikely to use in dangerous forms
more likely to be used Diluted with water to reduce risk
Halogens always form Diatomic molecules
Meaning a halogen molecule is made up from a pair of atoms
Florine = F2
Bromine = Br2
They all come in pairs because of the number of electrons each element has
all elements have 7 electrons on outer shell
Halogen elements gain a full outer shell by sharing pair of electrons which forms a covalent bond
Astotine is a very rare element
Reactivity in Group 7
Halogens are not stable and are always looking to gain an additional electron
To get this stability they would need to have a covalent bond turning into a halide ion
E.g. Chlorine can gain an electron to form a Chloride ion
A reduction reactions means atoms are gaining electrons
Sodium and Chlorine to make Sodium Chloride which is a stable ion
Group 1 and Group 7 pairing are very common
Lithium and Fluorine making Lithium Floride for example
Also Potassium and Bromine making Potassium Bromide
All halogens react in a similar way
Florine is the most reactive
Other halogens then decrease in reactivity
Colour changes when potassium ions go into Chlorine water, Bromine Water and Iodine water helps us tell the reactivity of a halogen
Potassium Bromine with Chlorine water, the solution turns to a Yellow orange Solution which is the colour of the bromine being produced
This shows chlorine is more reactive than Bromine
They need to become more stable by getting a full out of shell because they have 7 electrons and need one more
This is easier done for fluorine than iodine is because the of the size of the atoms
as moving down the group the atoms become larger
Because Iodine is bigger it means is harder to attract the extra electron it needs
The pattern in reactivity can also been see in the reaction with the halogens and hydrogen to form compounds called Hydrogen Halides
Reactions with Hydrogen
Fluorine - Occurs as soon as gases mix
Chlorine - A Burst of energy in the form of a flash of light is needed to begin the reaction
Bromine - Would need more energy (A Lighted splint) for them to be able to react
All hydrogen halides dissolve readily in water which shows the acidic nature of the compounds
The Noble Gases
Group 0 - Helium, Neon, Argon, Krypton, Xenon, Radon
They are all gases at room temperature
Boiling points below 0 C
Helium is -269
Boiling points increase as going down the group
This also applys for density. Helium would be lightest/Least dense
Helium is about 1/7 of the density of air
This is why Balloons with helium in them will float off
Xenon is 5 times heavier than air
A balloon with Xenon would sink if you let go of it
Noble gases are very unreactive
they are called inert because they were thought not to combine at all
The reason why the lack of reactivity is because of the number of electrons in the outer shell. They have a full outer shell so are not looking to combine to get a full outer shell like other groups
They are only to be discovered fairly recently because of their nonreactive nature
They are amongst the least reactive element known but they still are very useful.
Helium is used in air ships which is a safer alternative to hydrogen as it doesnt set on fire
Liquid helium is used to Cool metal coils so it's used more efficiently
Neon is used in lighting, When a high voltage passes through it, it glows
Argon is used in normal light bulbs to act as a shield around the metal so that the metal doesn't react with oxygen
The Periodic Table
Very useful to see patterns in reactions
Vertical columns are groups
Horizontal rows are periods
It is good to describe an element with its position (its group and its period)
In The Middle Of The Tile There Is A Symbol For The Element
On The Top There Is The Relative Atomic Mass (This is the larger number)
On The Bottom Is The Atomic Number (This is the smaller Number)
The Atomic Number Tells us the number of Protons in the Nucleus and Electrons orbiting the nucleus on the shells
The way of categorizing is easy. Elements that react in similar ways, Are in the same group and that shows by the way they have patters
History Of The Periodic Table
"The most elegant organisational chart ever devised"
Early chemists didnt have the luxury of the periodic table as it had not been established
Early scientists grouped elements into family's with Broadly similar properties.
Johann Wolfgang Dobereiner Placed elements in groups of 3
One of his Triads was made up from the reactive non metals, Chlorine, Bromine, Iodine
John Newlands in 1864 extended this with his law of octaves
He found that if you placed elements in order of increasing atomic weight then a pattern appeared but this wasn't the complete story as after about 20 elements this pattern broke down
Dmitri Mendeleev Grouped elements with similar properties
He thought some elements where missing to leave space for them so his pattern would continue
He would put some elements out of order so they would be with there familys
When sub-atomic particles were discoved in the early 2000s they started catagorising them with there atomic number rather than the atomic weight
this meant elements were grouped together with similar elements and none were "out of order"
CuO + HCl --> CuCl2 + H2O
Cannot Change already existing atoms
So
CuO + 2HCL --> CuCl2 + H2O
[75x35]+[25x37]
100
= 35.5