Electron Affinity
The shells are generally filled in order of increasing radius,
since the negatively charged electrons are attracted by the
positively charged protons in the nucleus.
Down the groups, atomic radius increases. This is because
there are more energy levels and therefore a greater
distance between protons and electrons.
● An atom's electron affinity as a measure of the attraction
that exists between the nucleus, which is positively
charged, and the electron, which is negatively charged.
● This implies that factors that tend to reduce this attraction
will also reduce electron affinity.
● An increase in atomic size leads to a decrease in
electron affinity because the incoming electron is added
further away from the nucleus, i.e. on a higher energy
level.
● As you go down a group, the outermost electrons are located
further and further away from the nucleus. This implies that
they feel less pull coming from the nucleus.
● On the other hand, an increase in effective nuclear charge
has the exact opposite effect.
● When you go across a period of the periodic table, atomic
number increases, but electrons are being added to the
same energy level.
● This means that an incoming electron will be more attracted
to the nucleus, which implies that the energy gain when it is
added to the atom will be more significant → electron affinity
increases.
3.1 Energy needed per mole to remove an electron from an atom in a gaseous phase.
3.2 Ionisation energy increases from left to right, across a period.
3.3.1 Be:1s2 2s2 B:1s2 2s2 2p1
3.3.2 B has a 2p energy level; 2p has a higher energy than 2s. Therefore less energy is needed to
remove the valence electrons from B as from Be.
OR
2s electrons are paired and 2p electron is unpaired. Therefore less energy needed to remove 2p
electron.
3.4 False, The energy is high because of filled s and porbitals.
3.5.1 Alkali-metals
3.5.2 Reactivity increases from top to bottom.
3.5.3 Ionisation energy decreases, thus less energy to
remove an electron. Therefore reactivity increases.
Melting Point
● The melting points is the amount of energy required
to break a bond(s) to change the solid phase of a
substance to a liquid.
● Generally, the stronger the bond between the atoms
of an element, the more energy required to break that
bond.
● Metals generally possess a high melting point.
● Most non-metals possess low melting points.
Reactivity
● The farther to the left and down the periodic
chart you go, the easier it is for electrons to
be given or taken away, resulting in higher
reactivity.
● Period - reactivity increases as you go from
the left to the right across a period.
● Group - reactivity decreases as you go down
the group.
End of 2nd of March lesson
A covalent bond, also called a molecular bond, is a
chemical bond that involves the sharing of electron pairs
between atoms.
Challenge: Draw electron diagrams for the following
molecules:
Chlorine gas (Cl2)
Ammonia (NH3),
When a positively
charged ion forms a
bond with a
negatively charged
ions and one atom
transfers electrons
to another.
Draw the electron shell diagram of Lithium and Fluorine
Draw the Lewis dot for magnesium oxide and
calcium chloride