Trends in the Periodic Table: ionisation energy, electronegativity, atomic radius, melting and boling poins

Essay by DookiHigh School, 11th grade June 2005

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Ionisation energy is the energy to remove the first electron from an atom in the gaseous state.

- Increases across a period as electron shells go from near empty to full.

- Decreases down a group as the outer electrons become further removed from the positive nucleus.

- The second ionisation energy is always greater than the first since the electron is now being removed from a positive ion.

Electronegativity is the relative power to attract electrons.

- Increases across a period as the number of protons increases so does the positive charge of the nucleus, thus a stronger attraction and electrons are being held more tightly.

- Decrease down a group as the negatively charged electrons repel each other and the 'invaders'. The more protons, the greater the number of occupied electron shells that shield the nucleus.

- Fluorine is the most electronegative element and when combined with caesium, will react violently.

Atomic Radius

- Decreases across a period because the number of positively charged protons in the nucleus increases, pulling the negative electrons in more tightly.

- Increases down a group as the number of electron shells increase.

Melting and Boiling Points

- Increases to Group IV, then rapidly decreases.

- Groups I and II (Metallic bond). Moderate to high

- Group IV (Covalent network solids). Very high

- Group VII (Diatomic covalent). Forces between molecules are weak so it's low.

- Group VIII (Monatomic gases). Only forces between atoms are weak dispersion forces so its very low