Outcome 1: Trends of the Periodic Table Flashcards
What is the trend in covalent radius across a period?
Covalent radius decreases
- increase in nuclear charge increases pull of electrons to nucleus so atom becomes smaller
What is the trend of covalent radius down a group?
Covalent radius increases
- increase in energy levels so increase in shielding of nucleus
What is ionisation energy?
The measure of the energy required to remove a mole of electrons from an atom
(in the gaseous state)
What is the second ionisation energy?
The energy required to remove a second mole of electrons from an atom
Why do the noble gases have the highest ionisation energy?
They are very stable due to their full outer electron shells.
Removing an electron would result in the atom becoming less stable
Why is the second ionisation energy higher than the first?
Removing an electron from a lower energy level which is held more tightly to the nucleus thus requiring more energy to remove
Removing from full energy shell
What is the trend in ionisation energy across a period?
Ionisation energy increases
- Covalent radius decreases as increase in nuclear charge/pull so more energy is required to remove e-
What is the trend in ionisation energy down a group?
Ionisation energy decreases
- Increase in covalent radius
- Increase in energy levels
- increase in shielding nucleus
so outer/valence electrons are held less tightly and easier to remove
Why does ionisation energy increase as more electrons are removed?
Electrons further away from the nucleus aren’t held as tightly so require less energy to remove
What is Electron Attachment Enthalpy?
Gaining electrons to form negative ions
First electron affinities are always what type of reaction?
Exothermic
What does electron affinity give?
a measure of the attraction between an incoming electron and the positive nucleus
What is the electron affinity trend going down a group?
The enthalpy value decreases as less energy is involved in the formation of a negative ion
What is electronegativity
A measurement of an element’s ability to attract electron pairs in a covalent compound
the higher the value, the greater the power of attraction
What is the trend for electronegativity across a group?
Electronegativity increases
- covalent radius decreases and increase in nuclear charge/pull
- easier to become negative rather than positive as electrons are held tighter
What is the trend for electronegativity down a group?
Electronegativity decreases
- Covalent radius increases, increasing energy levels, increase of shielding nucleus, valence electrons further away and attracted less tightly
- easier to become positive than negative
What type of bonding is present when the electronegativity pull is equal?
Pure covalent bonds
What type of bonding is present when electronegativity pull is unequal?
Polar covalent bonds
What is the difference in electronegativity for ionic bonds
Full transfer of electrons
Which atom do the electrons accumulate towards in a bond?
The atom with the higher electronegativity (greater pull of electrons)
What happens when both atoms have similar electronegativities?
There will be comparatively equal sharing of the electrons
What happens when there is a large difference between the electronegativities?
The bonding will be ionic as two ions will be formed (one positive, one negative)
What does it mean that a polar bond has a net dipole moment?
It has positive areas and negative areas within the molecule
