Explain the trends in ionization energy across a period and for Lithium vs. Beryllium.

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Explain why there is a general increase in the first ionisation energy on going from left to right across the period.

Identify the key factors influencing ionization energy across a period.

Across a period, the **nuclear charge** (number of protons) increases, while the electrons are added to the same principal energy level. This means the **shielding effect** by inner electrons remains relatively constant.

Explain the effect of these factors on electron attraction and energy required.

The increasing nuclear charge exerts a stronger pull on the valence electrons, causing the **atomic radius** to decrease. More energy is therefore required to remove an electron from the stronger attraction of the nucleus.

2. It is observed that the second ionisation energy of Lithium (Li) is higher than Beryllium (Be). Explain this observation.

Write the electron configurations and consider the first ionization for both elements.

Lithium (Li) has an electron configuration of $1s^2 2s^1$. After losing its first electron, it forms $\text{Li}^+$ with a stable electron configuration of $1s^2$, which is like Helium (a noble gas).  
Beryllium (Be) has an electron configuration of $1s^2 2s^2$. After losing its first electron, it forms $\text{Be}^+$ with an electron configuration of $1s^2 2s^1$.

Compare the energy required for the second ionization.
The second ionization energy of Li involves removing an electron from a very stable, full inner shell ($1s^2$ core electrons). This requires a significantly large amount of energy. In contrast, the second ionization energy of Be involves removing an electron from the $2s$ subshell of $\text{Be}^+$, which is still an outer valence electron, not a core electron. Therefore, the second ionization energy of Lithium is much higher than that of Beryllium.
3. Write down the name of the group of the elements having the highest first ionisation energy. The group of elements having the highest first ionization energy are the Noble Gases.
1. Write down the chemical formulae for: a) Calcium Carbonate Calcium is $\text{Ca}^{2+}$ and carbonate is $\text{CO}_3^{2-}$ . The charges balance, so the formula is: $\boxed{\text{CaCO}_3}$ b) Magnesium oxide Magnesium is $\text{Mg}^{2+}$ and oxide is $\text{O}^{2-}$ . The charges balance, so the formula is: $\boxed{\text{MgO}}$

Explain the trends in ionization energy across a period and for Lithium vs. Beryllium.

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Identify the key factors influencing ionization energy across a period.

Explain the effect of these factors on electron attraction and energy required.

Write the electron configurations and consider the first ionization for both elements.

Compare the energy required for the second ionization.

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