Electron structure / periodicity * MOD 3 LINKS*

How many electrons go into each shell

• 1st shell: 2e- 

• 2nd shell: 8e- 

• 3rd shell: 18e-

• 4th shell: 32e- 

Define orbital

a region within an atom that can hold up to two electrons with opposite spins

Where is the highest energy level?

• in the outer shell

• the larger number of shells, the higher the energy level of the shell and further it is from the nucleus

Describe s-orbitals

• sphere

• holds 2e-

• found on shell 1 onwards

Describe p-orbitals & subshells

• dumbbell shape

• orbital holds 2e-

• subshell is 3 p-orbitals

• subshell holds 6e-

• found on shell 2 onwards

Describe d-orbitals & subshells

• rectangle holds 2e-

• subshell is 5 rectangles and holds 10e-

• found on shell 3 onwards

Describe f-orbitals & subshells

• rectangle holds 2e-

• subshell is 7 rectangles and holds 14e-

• found on shell 4 onwards

What are the exceptions in electronic configuration

• Cr: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵

• Cu: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

→ makes d (half) full to make it stable 

Define 1st ionisation energy

amount of energy required to remove one electron from each atom in a mole of gaseous atoms

Give Mg 1-4 ionisation energies

• Mg₍𝓰₎ → Mg⁺₍𝓰₎  + e-

• Mg⁺₍𝓰₎ → Mg²⁺₍𝓰₎ + e-

• Mg²⁺₍𝓰₎ → Mg³⁺₍𝓰₎ + e-

• Mg³⁺₍𝓰₎ → Mg⁴⁺₍𝓰₎ + e- 

What factors affect ionisation energy?

• atomic radius

• nuclear charge (no. of protons)

• electron shielding

How does atomic radius affect IE?

• the greater the atomic radius, the weaker the electrostatic attraction between nucleus and outermost electrons

How does nuclear charge affect IE?

• the greater the nuclear charge, the greater the forces of attraction between the nucleus and electrons

How does shielding affect IE?

• inner shells electrons repel outer shell electrons → repulsion = shielding

• as the number of inner shells increase, shielding effect increases

• there is a weaker nuclear attraction between nucleus and outer electrons

What is the trend of 1st IE down groups?

• IE decreases down the group

• atomic radius increases 

• shielding increases 

• so there is less/weaker nuclear attraction between nucleus and outershell electrons 

What is the trend of 1st IE across periods?

• IE increases across period

• increased nuclear charge so atomic radius decreases

• so greater nuclear attraction between nucleus and OUTER electrons

• shielding remains the same / outer electrons are in the same shell

Why does it require more energy to remove each successive electron? 

• atomic radius decreases as same amount of protons attract fewer electrons

• nuclear attraction between remaining electrons and nucleus increases

Successive ionisation energy (potassium example)

• large increase indicates change of shell

• amount of e- lost in last shell indicate group number

• every element left with 2e- in inner shell

Why is there a decrease in energy from group 2-3? 

• Be outer electron is in s subshell whereas B outer electron is in a p subshell

• p subshell is in a higher energy level than s subshell so less energy is required to remove the e- 

Why is there a decrease in energy from group 5-6?

• N outer electron has 3e- in 3 p orbitals whereas O outer electron has 4e- in 3 p orbitals

• O has paired electrons in a p orbital which repel each other

• O has increased shielding

Whys there a sharp decrease in IE from the end of the period to the start of the next period

• there is a new subshell so outer electron is removed from a higher energy level

• increased shielding → increased atomic radius → less nuclear attraction

Whats periodicity

trend in physical and chemical properties that is repeated across each period

Why does the B/MP increase from Na-Al

• the charges of each ion increases and the number of delocalised electrons increase

• the ionic radius decreases

• so stronger ef attraction between +ve ions and -ve delocalised electrons

• more energy required to overcome

Why does Si have a higher MP than Al

• Si is a giant covalent structure and atoms held tightly by strong covalent bonds which require more energy to break

Why does Si have a higher MP than P

• Si is a giant covalent structure with atoms held tightly by strong covalent bonds

• whereas P is a simple molecular molecular structure which has weak VDW forces between molecules which requires less energy to break than Si

Why is there a general decrease in M/BP from P-Ar

• all simple molecular structures

• molecules held together by weak London forces

• requires a small amount of energy to break

Why is there a slight increase in M/BP from P-S

• S is bigger than P

• S has more e- so has stronger London forces 

• required more energy to break