Periodicity
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What is a group?
The vertical column of elements. The elements in a group have similar properties. The elements in a group have the same number of electrons in their outermost shell.
What is a period?
Horizontal rows of elements.
Describe the trend in atomic radius across a period.
Decreases. Nuclear charge increases. This increased charge pulls electrons in closer to the nucleus. Greater attraction.
Describe the trend in atomic radius down a group.
Increases Number of shells increases as you go down. Outer main level is further from the nucleus and atomic radii increase. Power of attraction between the outer electron and nucleus is reduced. Increased shielding
What is the first ionisation energy?
The energy required to convert one mole of a gaseous atom into a mole of positively charged gaseous ions.
First ionisation energy equation?
X(g) -> X^+(g) + e-
Describe the trend in first ionisation energy across a period.
Increases. Nuclear charge increases. Harder to remove an electron. Atomic radius decreases.
Describe the trend in first ionisation energy down a group.
Decreases. Number of shells increases. Electron being removed is further from the nucleus and so is easier to remove. Increased shielding.
Describe the melting points of sodium, magnesium and aluminium.
Metals with metallic bonding. Melting points increase due to greater positive charged ions. This means more electrons are released as delocalised electrons so the attractive electrostatic forces increase from Na to Al.
Describe the melting point of silicon.
Macromolecular Very strong covalent structure. Covalent bonds require a lot of energy to break. High melting point.
Describe the melting points of sulfur, phosphorus and chlorine.
Simple molecular. Held with weak van der waal forces. Don’t require much energy to overcome these weak forces. Low melting points.
Describe the melting point of argon.
Noble gas. Full outer shell of electrons. Very stable atom. Van der waal forces are very weak. Melting point is very low. Exists as a gas at room temperature.
What does the group number indicate on the periodic table?
Number of outer electrons of an element.
What is periodicity?
Repeating trends within the periodic table.
What does the melting point of period 3 elements depend on?
Bond strength Structure of the element
Why does S have a higher melting point than P?
S8 has more electrons than P4 so stronger van der waal forces.
Explain the pattern in the first ionisation energies of the elements from lithium to neon.
General Trend: - 1st IE increases due to an increased nuclear charge, similar shielding and electrons in the same shell so stronger attraction between nucleus and outer electrons. Deviation 1: - B lower than Be. Outer electron is in 2p and is higher in energy than 2s. Deviation 2: - O lower than N. 2 electrons in 2p need to pair. Pairing causes repulsion.