Periodicity Flashcards
periodicity is
a regularly repeating pattern of atomic, physical and chemical properties with increasing atomic number
the atomic radius of an element is a measure of
the size of its atoms
the atomic radius is
the distance from the centre of the nucleus to the boundary of the electron cloud
since the atom does not have a well defined boundary, we can find the atomic radius by
determining the distance between the two nuclei and dividing it by two
when measuring the atomic radius of atoms in a covalent bonds, we are measuring the
covalent radius (the atoms will be shown joined, close together)
measuring the radius of two atoms which are not bonded, but touching, is called the
van der Waals radius
for neon and argon, the only radius that can be determined is
the van der Waals radius as they do not bond with other elements
the radius used for metals is called the
metallic radius
when comparing atomic radii, always
compare like with like, as the van der Waals radius will always give a larger value
across a period, the atomic radius
decreases
the atomic radius across a period decreases because
the number of protons increases in the nucleus, so the nuclear charge increases too
elements with giant lattice structure have….melting and boiling points
high
elements with simple molecular structures have…..melting and boiling points
low
there are two anomalies for each period when plotting first ionisation energies on a graph:
group 3 and group 6
although the nuclear charge of born is greater than beryllium, boron has a lower first ionisation energy because
the outer electron has more energy, being in a 2p orbital as opposed to the 2s orbital for beryllium, therefore, less energy is required to remove it. boron’s outer electron also experiences a higher electron-electron repulsion
