3.4 - Thermochemical Principles And Properties Of Particles And Substances Flashcards
Isotopes
Various numbers of neutrons in an atom
Atomic number determined by..?
Number of protons.
Ionisation energy definition
Energy needed in kJ mol-1 to remove one electron from each atom in 1 mole at its gaseous state
Going down/across groups in Ionisation Energy
Across:
Number of protons will increase so more electrons are added in the same shell therefore the effective nuclear charge acting on the outermost electron is stronger.
Down:
Ionisation energy decreases as electron being lost is further away from the nucleus and has more shielding from inner electrons therefore electron is not held as strongly.
S subshell
Filling this gives extra stability to elements He, Be, Mg, Ca so first ionisation energy os above the trend
P subshell
Filling this gives N and P extra stability due to a higher value.
Ionic Radii
metals, non-metals, transition metals
Metals:
Groups 1-3 lose electrons forming +ve ions. Less shielding occurs so greater ENC. Ions are smaller than corresponding atom due to increased attraction.
Non-metals:
Gain electrons to form -ve ions. Therefore more electrons are in the same space creating more repulsion. Larger ionic radius.
Transition:
Groups 4-15 lose some outer electrons. They decrease their radii because there are fewer outer electrons (decreased repulsion). First electrons lost are from the valence shell therefore decreased size.
Atomic Radii definition
Calculated from the average distance between 2 atoms. Dependant on EDSeR.
EDSeR stand for?
Effective Nuclear charge - # protons in nucleus.
Distance of valence electrons from the nucleus.
Shielding - how many electrons between nucleus and valence shell.
Repulsion - of electrons (negative ions)
Atomic Radii
Down/Across
Down:
Electrons go into different energy levels (more shells), each shell is further away from the nucleus and increased shielding occurs due to more inner electrons. Radii gets bigger. Attraction between nucleus and valence electrons decreases.
Across:
Decreases due to increased ENC (more protons). Outside electrons are pulled closer to the nucleus. Similiar shielding effect due to same amount of energy shells between the nucleus and valence electrons. Radii gets smaller.
Electronegativity
Measure of attraction of an atom for a bonded pair of electrons.
Greater the Electronegativity, greater the pull on the electrons.
Polarity.
PEAS
EBELSDSO
Polarity
Electronegativity
Atoms
Symmetry
Electronegativity Bond type Electron clouds Lone pairs Shape Dipoles Symmetry Overall
Polar Covalent Bond Dipoles
Intermolecular forces - weak forces between molecules.
Temporary dipoles - temporary uneven distribution of electrons around an atom which repel electrons in nearby molecules inducing a small dipole. (Electrons move randomly)
Permanent dipoles - occurs between opposite ends of molecules. More polar a molecule, stronger the attraction.
Hydrogen bonds - strongest attraction force. Molecule must contain a H atom bonded to a F, O or N atom.
SHIP - Intermolecular Bonding
Shape
Hydrogen bonds
Instantaneous (temporary) dipoles
Permanent dipoles
Periodic table
- Atomic number increases across a period - protons increase.
- Atoms get smaller across a period - ENC increases, pulling electrons closer.
- Atoms become larger going down a group - # of electron shells increase. ENC decreases from shielding.
- Ions formed by elements on the left are smaller than their atoms as they lose electrons to have an empty shell.
- Ions formed by elements on the right are bigger as they have gained electrons increasing the repulsion between valence electrons.
