Topic 3: Periodicity Flashcards
How do you find the effective nuclear charge of an element?
Atomic number - inner electronseg. Na11 - 10 = +1
Define the atomic radius.
The distance from the nucleus to the outermost electrons of the Bohr atom.
Describe the trends of atomic radii in the periodic table.
Atomic radii decreases across a period because the nuclear charge increases while the number of shielding electrons remains constant. This means that the attraction between the nucleus and the outer electrons increases so the atomic radii decreases.Atomic radii increases down a group because the number of occupied energy levels increases.
Describe the trends of ionic radii in the periodic table.
Ionic radii decreases across a period from G1 to G14. These ions are isoelectronic. They have all lost electrons to gain a full valence shell. Across a period, a proton is successively added (increasing the nuclear charge) while the number of electrons stays the same. The added proton exerts a stronger pull on the electrons so the ionic radii decreases.Ionic radii decreases across a period from G14 to G17. These ions are isoelectronic. They have all gained electrons to fill their valence shell (with the exception of Si⁴⁺). Across a period, a proton is successively added (increasing the nuclear charge) while the number of electrons stays the same. The added proton exerts a stronger pull on the electrons so the ionic radii decreases. The discontinuity in G14 is because positive ions are smaller than negative ions because they have lost a energy level to gain a full valence shell. Ionic radii increases down a group as the number of occupied energy levels increases.
Define the first ionisation energy.
The energy required to remove one mole of electrons from one mole of gaseous ions to produce one mole of gaseous charged ions.
Describe the trends of ionization energy in the periodic table.
Ionization energy increases across a period. Across a period, a proton is successively added so the nuclear charge increases and the atomic radius decreases. This means there is a greater attraction between the nucleus and the outer electrons therefore it requires more energy to remove the outer electrons.Ionization energy decreases down a group. Down a group the number of occupied energy levels increases so the atomic radii increases, therefore there is a weaker attraction between the nucleus and the outer electrons. So it requires less energy to remove the outer electrons.
Why are there exceptions to the general trend of ionization energy across a period?
Due to the orbital that the outer electron occupies. For example, electrons in p orbitals have a higher energy and are further away from the nucleus than electrons in the s orbital so they require less energy to remove.Also, double occupied orbitals. The electrons repel each other so it requires less energy to remove one than an electron in a half filled orbital.
Define the first electron affinity.
The energy change when one mole of electrons is added to mole of of gaseous atoms to form one mole of gaseous -1 ions.
Describe the trends in electron affinity in the periodic table.
In general, the greater the atomic radius and the greater the electron shielding, the less energy is released when an electron is added.
Define electronegativity.
A measure of the attraction of an atom for a bonding pair of electrons.
Describe the trends in electronegativity in the periodic table.
Electronegativity increases across a period because protons are successively added so the nuclear charge increases. There is an increased attraction between the nucleus and the bonded electrons.Electronegativity decreases down a group because the number of occupied energy levels increases so the bonding electrons are further away from the nucleus. Therefore there is a reduced attraction.
Describe the trends in melting point in G1 and G17.
Melting point decreases down G1. The elements have a metallic structure held together by the attractive forces between the delocalised electrons and the positively charged ions. Down a group, the number of occupied energy levels increases so the atomic radii increases, decreasing the attraction. So less energy is needed to break the forces and trigger a change in state. Melting point increases down G17. The elements have a molecular structure held together by temporary dipoles. These increase with the number of electrons in the element.
What does the melting point of different elements depend on?
The structure of the element and the type of bonding.In increasing melting point:Molecular covalent - metallic bonding - giant covalent network.
Give the following information on the alkali metals.- Physical properties- Chemical properties- Storage- Reaction with water
Physical properties:- Good conductors of electricity and heat- Low density- Grey, shiny surface when freshly cut with a knife.Chemical properties:- Very reactive. Chemical reactivity of the alkali metals increases down the group because the valence electrons are further from the nucleus.Storage:- Stored in oil to prevent contact with air and water.Reaction with water:Alkali metal + water -> metal hydroxide + hydrogen
Give the following information on the halogens.- Physical properties- Chemical properties- Displacement reactions
Physical properties:- Coloured.Chemical properties:- Very reactive non-metals. Chemical reactivity decreases down the group.Displacement reactions:The reactivity of the halogens can be determined by placing them in direct competition for an extra electron. The more reactive molecule will become ionic.