3.2.1 Periodicity Flashcards
Define periodicity
Trends in the periodic table
What are periods and what do they show?
The rows across the periodic table, that tell us the number of energy levels that an atom of that element has. The periods show repeating patterns in chemical and physical properties.
What is the periodic table?
A list of all known elements, that are arranged in order of increasing atomic number (number of protons).
What are groups and what do they show?
The columns in the periodic table, which tell us the number of electrons in the outer energy level (valence electrons). Elements in the same group have similar chemical properties.
What are blocks and what do they show?
Blocks are a way of dividing the periodic table, to show which sub-shell (s,p,d or f) the outermost and highest energy electrons are in.
State and explain the trend in atomic radius across a period?
Across a period, atomic radius decreases.
-the number of protons, and so the nuclear charge increases
-shielding remains constant as all atoms have the same number of shells across a period.
-the attraction between the outer energy level electrons and the nucleus increases
-this pulls the electrons closer to the nucleus so atomic radius decreases.
State and explain the trend in atomic radius down a group
The atomic radius increases down a group
-the number of shells increases, so shielding increases
-the nuclear charge increases, but not by a significant amount
-the attraction between the outermost energy level electrons and the nucleus decreases
-therefore electrons are not pulled in as closely, so atomic radius decreases.
State and explain the trend in first ionisation energy across a period
Across a period, the first ionisation energy increases
-the nuclear charge increases
-the atomic radius decreases
-there are stronger forces of attraction between the nucleus and outer electrons
-this therefore makes it more difficult to remove an electron, so the first ionisation energy increases.
Which periods show exceptions to the rules of ionisation energy across a period?
Group 2 and group 3
-see ionisation notes
Describe and explain the trend in melting points from sodium to aluminium?
-Na, Mg and Al are all metallic elements
-atomic radius decreases across a period as seen
-nuclear charge increases across a period, as there are more protons in the nucleus
-the number of electrons in the outer shell increases, meaning the number of delocalised electrons increases
-there are stronger electrostatic forces of attraction between positive ions and delocalised electrons, which require more energy to overcome
-this means the mp increases from Na to Al.
What is the general trend of the melting points of period 3 elements?
Rises and then falls
Why does silicon have the highest melting point of the period 3 elements?
Because it is a macromolecular structure- each silicon atom forms 4 strong covalent bonds, which require lots of energy to overcome.
Describe and explain the trend in boiling points from P to Ar
-P, S, Cl and Ar exist as simple molecules
-these exist as P4, S8, Cl2 and Ar
-As molecules decrease in size, the van der waals forces decrease in strength.
-less energy is required to overcome these forces, which leads to a decrease in melting point from S to Ar.
NOTE: S has a higher melting point than P, as it is a larger molecule.
