Chemistry Module 3.1 Flashcards
In the early 1800s, what were the only ways to categorise elements?
In the early 1800s, the only two ways to categorise elements were by their physical and chemical properties and their relative atomic mass. This was due tot he fact at this time, they only knew how to measure the relative atomic mass.
In 1817, who attempted to group similar elements?
johann Dobereiner attempted to group similar elements - these groups were called Dobereiner’s triads. He saw that chlorine, bromine and iodine had similar characteristics. He also realised that the other properties of bromine (e.g. atomic weight) fell halfway between those of chlorine and iodine. He found other groups of three elements (e.g. lithium, sodium and potassium), and called the triads. It was a start.
In 1863, who made another table of elements?
An English chemist called John Newlands had the first good attempt at making a table of elements in 1863. He noticed that if he arranged the elements in order of mass , similar elements appeared at regular intervals - every eighth element was similar. He called this the law of octaves, and he listed some known elements in rows of seven so that the similar element s lined up as columns.
What was the issue with John Newlands table of elements?
The law of octaves broke down in the third row, with many transition metals like Fe, Cu and Zn disrupting the pattern.
Who created the first accepted version of the periodic table?
Russian chemist, Dmitri Mendeleev produced a better table, which isn’t far off from the one we have today. He arranged all the known elements by atomic mass, but left gaps in the table where the next element didn’t seem to fit. That way he could keep elements with similar chemical properties in the same group. He also predicted the properties of undiscovered elements that would go in the gaps correctly.
How is the periodic table arranged?
The periodic table is arranged into periods (rows) and groups (columns).
What do all the elements within a period have the same number of?
All the elements within a period have the same number of electron shells.
Define periodicty.
Periodicity is the repeating trends in the physical and chemical properties of the elements across each period.
What do all the elements within a group have the same number of?
All the elements within a group have the same number of electrons in their outer shell. This means they have similar chemical properties.
Split the periodic table into an s block, d block and p block.
{Correctly split periodic table}
Define what is means for an atom to be ionised.
When electrons from an atom have been removed it has been ionised.
What is meant by the first ionisation energy?
The first ionisation energy is the energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms.
Why is ionisation an endothermic reaction?
Ionisation is an endothermic reaction because you have to put energy in to a molecule to ionise it.
What is the equation for the 1st ionisation energy of an oxygen atom?
O (g) → O⁺ (g) + e⁻
What are the three most important points about ionisation energies?
- You must always use state symbols, (g), because ionisation energies are measured for gaseous atoms.2. Always refer to 1 mole of atoms, as stated in the definition, rather than to a single atom.3. The lower the ionisation energy, the easier it is to form an ion.
How does Nuclear charge affect ionisation energy?
The more protons there are in the nucleus, the more positively charged the nucleus is and the stronger the attraction for the electrons.
How does Atomic radius affect ionisation energy?
Attraction falls off very rapidly with distance. An electron close to the nucleus will be much more strongly attracted than one further away.
How does shielding affect ionisation energy?
As the number of electrons between the outer electrons and the nucleus increases, the outer electrons feel less attraction towards the nuclear charge. This lessening of the pull of the nucleus by inner shells of electrons is called shielding.
What does a high ionisation energy mean in an atom?
A high ionisation energy means there’s a strong attraction between the electron and the nucleus, so more energy is needed to overcome the attraction and remove the electron.
What happens to ionisation energies as you go down the group?
As you go down a group in the periodic table, ionisation energies generally fall, i.e. it gets easier to remove outer electrons.
Why do the ionisation energies fall as you go down the group?
feeIonisation energies go down a group because: Elements further down a group have extra electron shells compared to ones above. The extra shells mean that the atomic radius is larger, so the outer electrons are further away from the nucleus, which greatly reduces their attraction to the nucleus.The extra inner shells shield the outer electrons from the attraction of the nucleus.This provides evidence that electron shells really exist - a decrease in ionisation energy going down a group supports the Bohr model of the atom.
What is the general trend for the ionisation energies as you move across a period and why?
As you move across a period, the general trend is for the ionisation energies to increase - more energy is required to remove the outer electrons.This is because the no. of protons is increasing. As the positive charge of the nucleus increases, the electrons are pulled closer to the nucleus, making the atomic radius smaller.The extra electrons that the elements gain across a period are added to the outer energy level so they don’t really provide any extra shielding effect (shielding works with inner shells mainly).
What are the two exceptions to the general trend of ionisation energies increasing across a period?
There are two exceptions to the trend:The first ionisation energy decreases between groups 2 and 3, and between groups 5 and 6.
Why is there a drop in ionisation energy between groups 2 and 3?
- The outer electron in group 3 elements is in a p orbital rather than an s orbital.2. A p orbital has a slightly higher energy than an s orbital in the same shell, so the electron is, on average, to be found further from the nucleus.3. The p orbital also has additional shielding provided by the s electrons.4. These factors override the effect of the increased nuclear charge, resulting in the ionisation energy dropping slightly.
Why is there a drop in ionisation energy between groups 5 and 6?
- In the group 5 elements, the electron is being removed from a singly-occupied orbital when ionised.2. In the group 6 elements, the electron is being removed from an orbital containing two electrons.3. The repulsion between two electrons in an orbital means that electrons are easier to remove from shared orbitals.
What is the equation for the second ionisation energy of oxygen?
O⁺ (g) → O²⁺ (g) + e⁻
What happens to successive ionisation energies within each shell?
Within each shell, successive ionisation energies increase. This is because electrons are being removed from an increasingly positive ion, and there’s also less repulsion amongst the remaining electrons. So the electrons are held more strongly by the nucleus.
What causes ‘big jumps’ in successive ionisation energy?
The ‘big jumps’ in ionisation energy happen when a new shell is broken into - an electron is being removed from a shell closer to the nucleus.
How can one tell what group an element belongs to by looking at a successive ionisation energy graph?
One can find out what group an element belongs to from a successive ionisation energy graph by counting the electrons removed before the first big jump to find the group number.
How can one predict the electron configuration of an element by looking at a successive ionisation energy graph?
The graphs can also be used to predict the electronic configuration of an element. Working from right to left, count how many points there are between each big jump to find out how many electrons are in each shell, starting with the first.
What is a Giant covalent lattice?
A giant covalent lattice is a huge network of covalently bonded atoms. (They’re sometimes called macromolecular structures too.)
Give an example of an atom which can form a giant covalent lattice.
Carbon atoms can form this type of structure because they can each form four strong, covalent bonds.
What are different forms of the same element in the same state called?
Different forms of the same element in the same state are called allotropes. Carbon has several allotropes like diamond, graphite and and graphene.
How many carbon atoms does carbon bond to in diamond?
In diamond, each carbon atom is covalently bonded to four other carbon atoms. The atoms rearrange themselves in a tetrahedral shape - its crystal lattice structure.
What are the effects of carbon having lots of strong covalent bonds?
Because it has a lot if strong covalent bonds:1. Diamond has a very high melting point - it actually sublimes at over 3800 K.2. Diamond is extremely hard - it’s used in diamond tipped drills and saws.3. Vibrations can travel easily through the stiff lattice, so it’s a good thermal conductor.4. It can’t conduct electricity - all the outer electrons are held in localised bonds.5. it won’t dissolve in any solvent.
What other element also forms a crystal lattice structure with similar properties to carbon?
Silicon (which is in the same periodic group as carbon) also forms a crystal lattice structure with similar properties to carbon. Each silicon atom is able to form four strong, covalent bonds.
Give the feature of graphite’s structure that means it can be used as a dry lubricant and in pencils.
The weak forces between the layers in graphite are easily broken, so the sheets can slide over each other - graphite feels slippery and is used as a dry lubricant and in pencils.
Give the feature of graphite’s structure that means it’s able to conduct electricity.
the delocalised electrons in graphite aren’t attached to any particular carbon atom and are free to move along the sheets, so an electric current can flow.
Give the feature of graphite’s structure that means it can be used to make lightweight, strong sports equipment.
The layers are quite far apart compared to the length of the covalent bonds, so graphite is less dense than diamond and is used to make strong, lightweight sports equipment.
