Periodic Trends

Question 1

Define atomic radius.

Answer 1

Atomic radius is the distance the valence electrons are from the nucleus.This distance can be determined by measuring the internuclear distance between to atoms of the same element divided by 2. Given that atoms are considered to behave something like billiard balls (i.e. they behave as if they are spherical), the atomic radius is a good indication of the size of the atom.

Question 2

State the trend for atomic radius in relation to the periodic table.

Answer 2

Across the periodic table the atomic radius decreases; down the periodic table the atomic radius increases.

Question 3

Explain the trend for atomic radius.

Answer 3

Across the periodic table the nuclear charge increases, therefore the force of attraction between the nucleus and the valence electrons increases. Greater force of attaction pulls the valence electrons closer to the nucleus. As a result across the periodic table the atomic radius decreases.Down the periodic table, the number of shells occupied by electrons increases and therefore the valence electrons are further from the nucleus. Therefore down the periodic table the atomic radius increases.

Question 4

Define ionization energy.

Answer 4

Ionization energy is the energy required to completely remove an electron from an atom.

Question 5

State the trend for ionization energy in relation to the periodic table.

Answer 5

Across the periodic table the ionization energy in general increases; down the periodic table the ionization energy decreases.

Question 6

Explain the trend for ionization energy.

Answer 6

Across the periodic table the nuclear charge increases, therefore the force of attraction between the nucleus and the valence electrons increases. Greater force of attaction results in more energy required to remove an electon. As a result across the periodic table the ionization energy in general increases.Down the periodic table, the number of shells occupied by electrons increases and therefore the valence electrons are further from the nucleus. As a result the force of attraction between the valence electrons and the nucleus decreases. Therefore down the periodic table the ionization energy decreases.

Question 7

Define electronegativity.

Answer 7

Electronegativity is the attraction the nucleus has for a shared pair of electrons in a bond.

Question 8

State the trend for electronegativity in relation to the periodic table.

Answer 8

Across the periodic table the electronegativity in general increases; down the periodic table the electronegativity in decreases.

Question 9

Explain the trend for electronegativity.

Answer 9

Across the periodic table the nuclear charge increases, therefore the force of attraction between the nucleus and the valence electrons increases. Greater force of attaction results in a higher electronegativity. As a result across the periodic table the electronegativity in general increases.Down the periodic table, the number of shells occupied by electrons increases and therefore the valence electrons are further from the nucleus. As a result the force of attraction between the valence electrons and the nucleus decreases. Therefore down the periodic table the electronegativity decreases.

Question 10

Define isoelectronic series.

Answer 10

An isoelectronic series describes a collection of atoms or ions who all have identical electron configurations. For example, N^3-, O^2-, F^-, Na⁺, Mg²⁺, Al³⁺ all have the electron configuration 1s²2s²2p⁶. Although they have the identical electron configuration, they differ in size (in ionic radius). N^3- is the largest and Al³⁺ the smallest because from N^3- to Al³⁺ there is an increase in number of protons and therefore nuclear charge.

Question 11

Explain what happens to the radius when an atom is ionized to the corresponding cation and why.

Answer 11

When an atom is changed to a cation, the radius decreases. The main reason for this is a loss of an electron to form a stable cation usually results in one less shell being occupied by electrons. The electron configuration for Na is 1s²2s²2p⁶3s¹ and for Na⁺ 1s²2s²2p⁶.

Question 12

Explain what happens to the radius when an atom is ionized to the corresponding anion and why.

Answer 12

When an atom is changed to an anion, the radius increases. The main reason for this is a gain of one or more electrons. Given that the number of protons does not change but there are more electrons and enhanced repulsion, this repulsion makes the electron “cloud” larger and thus the anion is larger than the corresponding atom.