The Periodic table Flashcards
(38 cards)
What did Johann Dobereiener do?
1817 - attempted to group similar elements - Dobereiners triads.
Saw Chlorine, Bromine and iodine had similiar characteristics.
Lithium, sodium and potassium.
Saw that bromine atomic weight fell between chlorine and iodine.
What did John Newlands do?
1863- noticed if he arranged elements in order of mass, elements with similar chemical and physical properties appeared at regular intervals.
The law of octaves, and listed known elements in rows of 7 so similar were in columns.
What is the Periodic Law?
The law of octaves developed into this.
States that if you arrange elements in order of increasing atomic number then their chemical and physical properties will repeat in a systematic way that can be predicted.
But the pattern broke down on the third row.
What did Mendeleev do?
1869 - built on Newlands, by leaving gaps in the table where the next element didn’t fit.
So elements with similar chemical properties were in the same groups.
He predicted the properties of missing elements, and was correct.
What are periods?
All the elements in a period (row) have the same number of electron shells.
This results in a repeating pattern of physical and chemical properties across a period (periodicity).
What are groups?
All elements in a group have the same number of electrons in their outer shell.
So they have similar physical and chemical properties.
Group number tells the number of electrons in the outer shell.
What are the blocks of elements?
s-block elements have an outer shell electron configuration of s1 or s2.
p-block have configuration of s2p1 to s2p6.
d-block have configurations in which d-sub shells are being filled.
What is first ionisation energy?
The energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms.
How should ionisation energies be written?
Use the gas state symbol (g).
Always refer to one mole of atoms.
The lower the ionisation energy, the easier to form an ion.
What is high ionisation energy?
There is strong electrostatic attraction between the nucleus and the electron, so more energy is needed to overcome the attraction and remove the electron.
How does nuclear charge affect ionisation energy?
The more protons 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 ones 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.
What is the trend in ionisation down a group?
Ionisation energies generally fall.
Elements further down have extra electron shells, so atomic radius is larger, and inner shells shield the outer electrons from the attraction.
The increasing nuclear charge is overridden by this.
What is periodicity of ionisation energy?
Ionisation energies generally increase across a period.
Nuclear charge increases, and all the extra electrons are at the same energy level, so similar shielding and atomic radius.
What are the differences in ionisation energies in groups?
The drop in energy between Groups 2 and 4 is due to the extra electrons in group 3 elements being in a p-orbital. Increases shielding and energy level.
The drop between 5 and 6 is due to electron repulsion.
What is electron repulsion?
Electron pairs around a central atom tend to orient themselves as far apart as possible.
Electrons removed from a shared orbital means electrons are easier to remove than from singly occupied orbitals.
What are successive ionisation energies?
Each time an electron is removed.
Second ionisation of oxygen: O+ (g) –> O^2+(g) +e-
What is the trend of ionisation energies in shells?
Within each shell, successive ionisation energies increase.
More electrons are being removed from an increasingly positive ion.
There’s less repulsion, so more energy needed.
Big jumps happen when a new shell is broken into - an electron is being removed from a shell closer to the nucleus.
How do you use graphs to find groups?
Count how many electrons are removed before the first big jump to find the group number.
What are giant covalent lattices?
Large networks of covalently bonded atoms.
Carbon and silicon both form 4 strong covalent bonds.
What is the structure of graphite?
The carbon atoms are sheets of flat hexagons with 3 covalent bonds.
The fourth electron is delocalised.
The sheets are bonded by weak induced dipole dipole forces.
What are the properties of graphite?
The weak forces are easily broken so it’s slippery - dry lubricant and pencils.
Delocalised electrons move along sheets - carry electron flow.
Layers are far apart so has low density, used to make strong, light sports equipment.
The strong covalent bonds give it a high melting point.
It is insoluble.
What is the structure of diamond?
Each carbon atom is covalently bonded to 4 other carbons.
Arranged in a tetrahedral shape.
