Periodic Trends Flashcards
Who made periodic table and how did he group the elements?
Dmitri Mendelev.
Going in order of atomic number.
Grouped elements in vertical groups.
Features of metal.
Malleable, ductile, conduct electricity and heat.
Define malleable.
Can be moulded into a shape.
Define Ductile
Can be pulled into thin wire.
What is an isotope?
Atoms of sake element with same number of protons but can have different number of neutrons.
Why can isotopes have different physical properties?
Physical properties depend on atomic mass, which varies due to different neutron number.
Rules for Relative atomic mass?
Done to 3 decimal places.
Has no units.
Define Relative atomic mass.
Weighted mean of atomic masses of an elements isotopes.
Relative atomic mass equation?
Percentage in question divided by 100. Multiply by atomic mass of isotope (number on top).
Do for each isotope and add it up for answer.
Trend of atomic radii.
Across period:
- more protons and electrons added
- electrons added to do e P and S sub shells so no size increase.
- Number of protons increases across period, positive charge of nucleus increases. So electrons are pulled closer to nucleus as Van Der Waal attraction is higher so atomic radius decreases.
Down groups:
- Atomic radii increases
- extra electrons added to match higher proton numbers so shells increase so so does radius.
Nuclear charge does increase but shells shield nuclear attraction. So radius can’t reduce as attraction is intercepted.
- Due to this atomic radius continues to increase.
Define Ion and Ionisation.
Ion - charged atom
Ionisation - Atom losing or gaining electrons and becoming charged resultantly.
Trends for Ionisation energies.
Across period:
- Each group 2 element has an extra shell to one above.
- Extra shells shield outer electrons from attractive of nucleus.
- More outer shells means outer electrons are further away from nucleus so nuclear attraction decreases.
- So potential energy needed to ionise atom becomes less age less.
- Across period attraction is stronger as protons increase so potential energy (ionising energy) required to break attraction and ionise atom also increases.
Down groups:
- S-block elements have a large atomic radii so a low value for ionisation energy.
- As atomic radii increases down groups there’s a decrease in value for ionisation energy. (Due to extra shields shielding).
E.g
- Group 1 elements have one electron in outer shell
- Energy required to remove that electron is low.
- means elements easily form +1 ions.
Second ionisation energy is greater as next electron that needs to be removed is from inner shell which is closer to nucleus.
Trend of melting points.
Depends on elements structure and bonding.
Higher can Der Waal energy = higher melting point.
More atoms in molecule means stronger van Der Waal forces = higher melting point.
Across period:
- stronger attraction so harder to break attraction and harder to melt as higher energy therefore temperature needed.
Decreases down group:
- Group 2 elements have a metallic structure with positive ions surrounded by delocalised electrons from outer electron shells.
- Down group metal ions get larger but ion charge and delocalised electron number is always +2 and 2.
- Larger ionic radius means delocalised electrons are further away from positive nuclei so they feel less attraction. So takes less energy to break bonds, so melting point generally decreased as you go down group.
Define delocalised electrons.
Electrons not associated with a single atom or covalent bond.
True or false? Larger atoms have smaller ionisation energies?
True.
