Periodicity | OCR A Level Chemistry

How are elements arranged in the periodic table?

In order of increasing atomic number.

What determines the block (s, p, or d) of an element?

The orbital in which the highest energy electron is located.

What is the trend for atomic radius across a period?

It decreases from left to right due to increased nuclear charge attracting electrons in the same shell.

Define first ionisation energy.

The energy required to remove one mole of electrons from one mole of gaseous atoms.

What are the three main factors affecting ionisation energy?

Nuclear attraction (number of protons), distance from the nucleus, and shielding by inner shells.

Why do successive ionisation energies increase?

The ion becomes smaller and the proton-to-electron ratio increases, leading to stronger electrostatic attraction.

What does a large jump in successive ionisation energies indicate?

The removal of an electron from a new, inner shell closer to the nucleus.

Why does Helium have the highest first ionisation energy?

Its electrons are in the first shell with no shielding and it has a high nuclear charge relative to its size.

Why do first ionisation energies decrease down a group?

Outer electrons are in shells further from the nucleus and experience more shielding.

Why is there a small drop in ionisation energy from Mg to Al?

Al's outer electron enters a 3p subshell, which is higher in energy and slightly shielded by 3s electrons.

Why is there a small drop in ionisation energy from P to S?

In sulfur, the 4th electron in the 3p subshell pairs with another, causing electron-electron repulsion that makes it easier to remove.

Define metallic bonding.

The electrostatic force of attraction between positive metal ions and delocalised electrons.

What three factors increase the strength of metallic bonding?

More protons, more delocalised electrons, and smaller ion size.

Why does Magnesium have a higher melting point than Sodium?

Mg has more delocalised electrons, a smaller ion, and a higher nuclear charge, leading to stronger metallic bonding.

Describe the structure of diamond.

A macromolecular structure where each carbon atom forms four covalent bonds in a tetrahedral arrangement.

Describe the structure of graphite.

A macromolecular structure with planar layers of carbon atoms where each atom forms three covalent bonds, leaving one delocalised electron per atom.

Why do macromolecular structures have very high melting points?

A large amount of energy is required to break the many strong covalent bonds throughout the giant structure.

Why is graphite a good conductor of electricity?

It contains delocalised electrons between its layers that are free to move.

Why are metals malleable?

The positive ions are identical, allowing planes of ions to slide over one another without breaking the metallic bonds.

Why do simple molecular substances like Cl2 have low melting points?

They are held together by weak London forces which require little energy to overcome.

Why does S8 have a higher melting point than P4?

S8 has more electrons, resulting in stronger London forces between molecules.

What is the general trend for melting points across Period 3?

They increase from Na to Al (metallic), peak at Si (macromolecular), and decrease for P, S, Cl, and Ar (molecular).

Are metals generally soluble in water?

No, they are insoluble.

What is the electronic configuration of Phosphorus?

1s2 2s2 2p6 3s2 3p3.

What is the electronic configuration of Sulfur?

1s2 2s2 2p6 3s2 3p4.

What is the primary reason for the general increase in ionisation energy across a period?

Increasing nuclear charge with the same shielding effect.

Why is Na's first ionisation energy lower than Neon's?

Na's outer electron is in a 3s shell, which is further from the nucleus and more shielded than Neon's 2p electrons.