Elements of Life Flashcards
What are atoms made up of?
Protons, Neutrons and Electrons
What are the charges for the Subatomic particles?
Proton = +1
Neutron= 0
Electron= -1
What is the relative mass for the subatomic particles?
Proton= 1
Neutron= 1
Electron= 1/2000
What is an ion and what does it mean when it has a negative or positive charge?
An ion is an atom with different numbers of protons and electrons. They either lose or gain electrons in order to have a full outer shell. Negative charge means there is one more electron than proton and positive have fewer electrons than protons.
What is an isotope?
Isotopes of an element are atoms with different number of neutrons, meaning the atomic number remains the same, but the mass number changes.
What decides the chemical properties of an element?
The number and arrangement of electrons.
What to the physical properties of an element often depend on?
The mass of the atom
How did John Dalton describe the structure of the atom and when?
He described them as being solid spheres at the start of he 19th century
How did J J Thomson describe the structure of the atom and when?
He describes them as being a positively charged sphere with negative electrons embedded in it (THE PLUM PUDDING MODEL!!) in 1897
How did Ernest Rutherford and his students Hans Geiger and Ernest Marsden prove the Plum Pudding Model incorrect and when?
By conducting the Geiger-Marsden experiment which involved firing alpha particles (positively charged) at an extremely thin sheet of gold in 1909
What were the results from the Geiger-Marsden experiment?
Most of the particles passed straight through the gold atoms and a very small amount were deflected (through more than 90 degrees)
What was the model that Rutherford came up with?
- There is a tiny, positively charged nucleus at the centre of he atoms where most of the mass is concentrated
- The nucleus is surrounded by a “cloud” of freely orbiting negative electrons
- Most of the atom is empty space
What did Henry Moseley discover and how did that effect how the nucleus was modelled?
He discovered the charge of the nucleus increased from one element to the other by units of 1, leading to Rutherford discovering that the nucleus contained positively charged particles called protons
What did James Chadwick discover?
He discovered the neutron
What were the 4 basic principles of Niels Bohr’s model?
- Electrons can only exist in fixed orbits (or shells)
- Each shell has a fixed energy
- When an electron moves between shells, electromagnetic ration is emitted or absorbed
- Because the energy of shells is fixed, the radiation will have a fixed frequency
How did the Bohr model also explain why some elements (the noble gases) are inert?
The shells of an atom can only hold a fixed number of electrons and that an elements reactivity is due to its electrons. When an atom has full shells, it is stable and doesn’t react.
What is the most accurate model we have today and what does it describe?
The most accurate model today involves quantum mechanics and basically shows that you never know where an electron is and which direction it’s going, but you can say how likely it is to be somewhere and electrons can act as waves as well as particles
What is relative mass?
The average mass of atoms of an element on a scale where an atom of carbon-12 is 12
Why do we uses relative mass?
Because the actual mass of an atom is very, very tiny and too small to weigh
What is relative isotopic mass?
The mass of an atom of an isotope of an element on a scale where an atom of carbon-12 is 12
How can you measure Relative Mass?
By using a mass spectrometer
What can a mass spectrometer be used to measure?
relative atomic mass, relative molecular mass, relative isotopic abundance and molecular structure
What are the 4 things that happen in a mass spectrometer?
- Vaporisation
- Ionisation
- Acceleration
- Detection
What occurs during the first step of mass spectrometry?
Vaporisation- the sample is turned into gas using an electrical heater.
What occurs during the second step of mass spectrometry?
Ionisation- the gas particles are bombarded with high energy electrons to ionise hem. Electrons are knocked off the particles, leaving positive ions
What occurs during the third step of mass spectrometry?
Acceleration- the positive ions are accelerated by an electric field
What occurs during the fourth step of mass spectrometry?
Detection- the time taken for the positive ions to reach the detector is measured. This depends on an ions mass and charge. Light highly charged will reach the detector first whilst heavier ions with small charge will take longer. For each sample, a mass spectrum is produced
What is on the Y axis of a mass spectrum?
The abundance of the icons as a percentage. The height of each peak gives the relative isotopic abundance
What is on the X axis of a mass spectrum?
The units are given as mass/charge ratio. Because the charge is mostly 1+ on the ions, you can often assume it is simply relative mass
How do you calculate the %relative isotopic abundance?
relative abundance/ total relative abundance x100
What is the equation that links number of moles, number of particles and Avogadro’s constant?
Number of moles= number of particles you have/ Avogadro’s constant
What is the equation that links number of moles, mass and molar mass?
n=m/Mr
What is the equation that links number of moles, volume and concentration?
n=VxC
What do ionic equations show?
Ionic equations only show the reacting particles and the products they form
What is an empirical formula?
The smallest whole number ratio of atoms in a compound
What is a molecular formula?
The actual numbers of atoms in a compound
What is the equations for percentage composition?
Percentage composition of element X= Total mass of element in compound/ total mass of compound x100
What is the theoretical yield?
The mass of product that should be made in the reaction if no chemicals are lost in the process
How can you find the theoretical yield?
By using the mole equations and the full balanced equation
What are some reasons why actual yield is never 100%?
- Not all the starting chemicals react fully
- Some chemicals are always lost
e.g. solution left on the filter paper, lost during transfer
What is the equation for percentage yield?
Percentage yield= actual yield/ theoretical yield x100
What is the standard solution and why does it have to be a suitable concentration?
The standard solution is the solution you know the concertation of. If it’s too dilute, you’ll have to add a lot until you neutralise the unknown solution. If its to concentrated, tiny amounts will cause a large pH change, making results inaccuarte.
What do we use titrations for?
To find exactly how much acid is needed to neutralise a quantity of alkali.
What are the 2 main indicators we use and what is the colour change they produce?
- Methyl orange: yellow to red when adding acid to alkali
- Phenolphthalein: Red to colourless when adding acid to alkali
Why don’t we use universal indicator in titrations?
Its colour change is too gradual
How many electrons can each subshell hold in total?
Each orbital only holds up to 2 electrons. In total:
S-shells hold 2
P-shells hold 6
D-shells hold 10
F-Shells hold 14
What are the orbital shells for each subshell?
S-Shells = spherical
P-Shells = dumbbell shape on the axis
D-Shells= dumbbell shape in between the axis
What are the rules when filling electron shells?
- Electrons fill up the lowest subshell first
- Electrons fill orbitals singly before they start pairing
- 4s subshell has a lower energy level than 3d subshell meaning it fills up first. However, the 4s subshell empties before the 3d shell
How does the electron configuration of ions differ?
They are the same but you either add of remove to or from the highest energy occupied subshell.
What is ionic bonding?
When ions are bonded together by electrostatic attraction
What is electrostatic attraction?
The forces that hold positive and negative ions together. When ions are held together like this, it’s called ionic bonding
What occurs between the ions in a giant ionic structure?
Within the lattice of a giant ionic structure, ions with different charges are attracted to one another whilst the ions with the same charge repel one another.
How are the ions arranged in a giant ionic sructure?
The ions arrange themselves to maximise attractions and minimise the repulsion
What are the properties of ionic compounds?
- Conduct electricity when molten or dissolved
- They have high melting points
- Often soluble in water
How does the ionic structure describe the properties?
- The ions in a liquid/solution are free to move, meaning the charge also moves, allowing it to conduct electricity
2.Giant ionic lattices are held together by strong electrostatic forces which take a lot of energy to overcome - Water molecules pull the ions away from the lattice because they are polar whereas part of the molecule has a small negative/ small positive charge, meaning they’re soluble in water.
What is covalent bonding?
When atoms share electrons with one another so they’ve all got a full outer shell
When does covalent bonding occur?
Between non-metals (ionic is between a metal and non-metal)
What is occurring between the nuclei and electrons/ nuclei and nuclei?
-Both positive nuclei are attracted electrostatically to the shared electrons
-There is repulsion occurring between the two positive nuclei
-To maintain covalent bonding, there has to be a balance between repulsion and electrostatic attraction
What are the properties of molecular substances?
- Fairly low melting and boiling point as there is no giant structure to overcome
- They don’t conduct electricity as there is no charge carriers that are free to move
- Usually insoluble in water as the polar water molecules are more attracted to each other rather than the molecular substance (some exceptions)
What is dative (or coordinate) bonding?
When both electrons come from one atom in covalent bonding e.g. Ammonium ion (NH4+). This is shown in diagrams by an arrow pointing to the “donor” atom
What are giant structures made up of?
Covalently bonded atoms where the electrostatic attractions holding the atoms together are much stronger than the ones between simple covalent molecules
What are 2 elements that form giant covalent structures?
Silicon and Carbon
What are the properties of giant covalent structures?
- Very high melting point
- Extremely hard
- Good thermal conductors
- Can’t conduct electricity
What is one acceptation to the “can’t conduct electricity” rule
Graphite- carbon atoms form sheets with each atom sharing 3 of its outer shell electrons with 3 other carbon atoms, leaving the 4th electron in each atom fairly free to move between the sheets, making it a good conductor
What is the structure of giant metallic lattice?
- The outer shell electrons of the metals are delocalised meaning they’re free to move, leaving a positive metal ion
- The positive metal ions are attracted to the negative delocalised electrons meaning they form a lattice of closely packed positive ions in a sea of electrons
What are the properties of metals?
- High melting points (more electrons means higher melting point)
- Fairly mailable (no bonds meaning metal ions can slide over one another)
- Good thermal conductors (delocalised electrons can pass kinetic energy to each other)
- Good electrical conductors (delocalised electrons can pass charges)
- Insoluble, except in liquid metal ( strength of metallic bonds)
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