Question

a) Define the following terms [2]

i) Electronegativity ii) Ionisation potential.

b) (i) What changes occur in the atomic size of third elements from Sodium to chlorine across the

period. [1X5]

ii) Describe the change in metallic character (1) across the period (2) down the group.

iii) How does Ionisation potential vary while going down the group of alkali metals from lithium to

Caesium.

iv) How does the electron affinity of the halogen group vary​

Answer 1

Answer:

Explanation:

i) Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to cesium and francium which are the least electronegative at 0.7.

ii) Ionization potential  or ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule is called an ion.

Answer 2

Answer:

a)I) Electronegativity, symbol χ, measures the tendency of an atom to attract a shared pair of electrons (or electron density). An atom's electronegativity is affected by both its atomic number and the distance at which its valence electrons reside from the charged nucleus.

ii)The second ionisation energy is the energy required to remove the electron from the corresponding mono-valent cation of the respective atom. Oxygen has greater second ionisation energy than fluorine.

b) I)Across the period, the valence electrons for each atom are in the 3-level. They are screened by the same inner electrons. The only difference is the number of protons in the nucleus. From sodium to chlorine, the number of protons steadily increases and so attracts the bonding pair more closely.

ii) As the effective nuclear charge acting on the valence shell electrons increases across a period, the tendency to lose electrons will decrease. Down the group, the effective nuclear charge experienced by valence electrons decreases because the outermost electrons move further away from the nucleus. Therefore, these electrons can be lost easily. Hence, metallic character decreases across a period and increases down a group.

iii)The ionization enthalpies of the alkali metals are considerably low and decrease down the group from Li to Cs. This is because the force of attraction between nucleus and the outermost electron is reduced due to intervening of inner electrons.

iv)Since the atomic size increases down the group, electron affinity generally decreases (At < I < Br < F < Cl). An electron will not be as attracted to the nucleus, resulting in a low electron affinity. However, fluorine has a lower electron affinity than chlorine.