Chapter 7- Trends in the Periodic Table

Question 1

Define Atomic Radius:
Define Bond Length

Answer 1

The atomic radius of an atom is half the distance between the nuclei of two atoms of the same element that are joined together by a single covalent bond.
Bond length is the full distance

Question 2

Does The atomic radius of a bond increase or decrease across a group? Explain your answer: (2 reasons)

Answer 2

Reason 1 - No increase in screening effect.
Extra electrons added when moving across a period go into the same outer energy level so no increase in screening.

Reason 2 - Increase in effective nuclear charge.
When the number of protons in the nucleus is increasing there is a greater attractive force on the outer electrons.

Question 3

Define screening effect

Answer 3

The Screening Effect of electrons occurs as the electrons in the inner energy levels screen the outer electrons from the positive charge of the nucleus.

Question 4

Define nuclear charge

Answer 4

Nuclear charge is the attraction between negative electrons and positive protons.

Question 5

Does The atomic radius of a bond increase or decrease down a group? Explain your answer: (2 reasons)

Answer 5

It increases

Reason 1: New energy levels
Additional electrons are going into a new energy level which is further from the nucleus. Making the atomic radius bigger.

Reason 2: Screening effect
The outer electron is shielded from the pull of the positive protons due to the full inner orbits. Thus counteracting the increase in the nuclear charge.

Question 6

Why don’t Nobel gases have an atomic radius?

Answer 6

Nobel gases don’t form atomic radii as they are stable, so intramolecular bonds don’t exist.

Question 7

Define First Ionisation Energy

Answer 7

The first ionisation energy of an atom is the minimum energy required to completely remove the most loosely bound electron from a gaseous atom in its ground state.
X(g) → X+(g) + e-

Question 8

Define Second Ionisation Energy

Answer 8

The second ionisation energy is the energy required to remove an electron from agaseous ion with one positive charge in its ground state.
X+(g) → X2+(g) + e-

Question 9

Does the 1st ionisation energy increase or decrease across a period? Explain why: (2 reasons)

Answer 9

It increases

Reason 1: Increasing nuclear charge
The most loosely bound electron gets pulled more strongly by the nucleus. More energy is needed to remove this electron.

Reason 2: Decreasing atomic radius
The most loosely bound electron gets closer to the nucleus so the nucleus has a stronger pull on the electron. More energy is needed to remove the electron.

Question 10

Does the 1st ionisation energy increases or decrease down a period? Explain why: (2 reasons)

Answer 10

It decreases

Reason 1: Increasing atomic radius
The outermost electron gets further and further from the nucleus, making it easier to remove.

Reason 2: Increasing screening effect
Electrons in the inner energy level(s) shield the outer electrons from the positive charge in the nucleus. Outermost electrons are easier to remove.

Question 11

What is the exception to the general ionisation values trend?

Answer 11

Any half full P sub-level or full D sub-level has extra stability thus slightly higher ionisation values. (Be, N, Mg, P).

Question 12

Define Electronegativity

Answer 12

Electronegativity is the relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond

Question 13

Does electronegativity increase or decrease across a period?
Give a reason for your answer:

Does Electronegativity increase or decrease down a group?
Give a reason for your answer:

Answer 13

It increases because of the growing nuclear charge and decreasing atomic radius.

It decreases because of the increasing atomic radius and screening effect (alkali metals).

Question 14

What are some trends among the Alkali Metals: (8 listed)

Answer 14

Reactivity increase down the group
Very reactive – stored under oil
Extracted from compounds or ores
Low ionisation energy and electronegativity value.
Form ionic bonds as tend to loose electrons
React with oxygen to form oxides
React with water to form hydroxides and hydrogen gas
React with HCl to form chlorides and hydrogen gas.

Question 15

What are some trends among the halogens: (5 listed)

Answer 15

Reactivity decreases down the group
Highly electronegative and most reactive in Periodic Table
Do not exist free in nature.
F is more reactive than Cl, Br, I, etc.

Boiling points increase down the group due to Van der Waals forces existing between atoms and bigger atoms needing more energy to break them apart.