Question

w3: periodic properties

1. net attractive force:

a) the net attractive force within an atom from left to right.
explanation:
b) the net attractive force within an atom from top to bottom.
explanation:

1. atomic radius

a) define atomic radius:
b) atomic radius from left to right.
c) atomic radius from top to bottom.
d) which of the following atoms has the largest atomic radius?
k f be ne cs n
e) which of the following atoms has the smallest atomic radius?
s ca si rb k ge

Explanation:

1. Net attractive force

a)

• Step1: Analyze the trend across a period (left - right)

As we move from left to right across a period in the periodic table, the atomic number increases. The number of protons in the nucleus increases (positive charge increases), and the electrons are added to the same principal energy level. The shielding effect (due to inner - shell electrons) remains relatively constant. The effective nuclear charge (\(Z_{eff}=Z - S\), where \(Z\) is the atomic number and \(S\) is the shielding constant) increases. Since the net attractive force is related to the effective nuclear charge, the net attractive force within an atom increases from left to right.

b)

• Step1: Analyze the trend down a group (top - bottom)

As we move from top to bottom in a group, the number of electron shells (principal energy levels) increases. Although the atomic number (number of protons) increases, the shielding effect (due to the increasing number of inner - shell electrons) also increases significantly. The increase in shielding almost cancels out the increase in nuclear charge. So, the net attractive force within an atom decreases from top to bottom.

2. Atomic radius

a)

Atomic radius is defined as half the distance between the nuclei of two identical atoms bonded together (for non - metals in covalent bonds) or half the distance between adjacent nuclei in a metal lattice (for metals).

b)

• Step1: Relate to net attractive force across a period

Since the net attractive force (effective nuclear charge) increases from left to right across a period, the electrons are pulled more closely towards the nucleus. So, the atomic radius decreases from left to right.

c)

• Step1: Consider the number of electron shells down a group

As we move from top to bottom in a group, the number of electron shells increases. The increase in the number of shells has a more dominant effect than the increase in nuclear charge (due to shielding). So, the atomic radius increases from top to bottom.

d)

• Step1: Locate the elements in the periodic table
• \(K\) (potassium) is in period 4, group 1.
• \(F\) (fluorine) is in period 2, group 17.
• \(Be\) (beryllium) is in period 2, group 2.
• \(Ne\) (neon) is in period 2, group 18.
• \(Cs\) (cesium) is in period 6, group 1.
• \(N\) (nitrogen) is in period 2, group 15.

Since atomic radius increases down a group and \(Cs\) is the lowest (in terms of period number among the given elements) in its group (group 1), the atom with the largest atomic radius is \(Cs\).

e)

• Step1: Locate the elements in the periodic table
• \(S\) (sulfur) is in period 3, group 16.
• \(Ca\) (calcium) is in period 4, group 2.
• \(Si\) (silicon) is in period 3, group 14.
• \(Rb\) (rubidium) is in period 5, group 1.
• \(K\) (potassium) is in period 4, group 1.
• \(Ge\) (germanium) is in period 4, group 14.

Since atomic radius decreases from left to right across a period. Among \(S\) (period 3, group 16), \(Si\) (period 3, group 14), and considering the other elements (\(Ca\), \(Rb\), \(K\), \(Ge\) which are in higher periods), the atom with the smallest atomic radius is \(S\).

Answer:

1.
a) increases
b) decreases
2.
a) Half the distance between the nuclei of two identical atoms bonded together (for non - metals in covalent bonds) or half the distance between adjacent nuclei in a metal lattice (for metals)
b) decreases
c) increases
d) \(Cs\)
e) \(S\)