Periodicity and Periodic Table Flashcards
Define isotopes and radioisotopes
Atoms with same no. of protons but different no. of neutrons are isotopes. Same chemical properties, but have different physical properties due to difference in mass.
Isotopes that are stable do not emit radiation, unlike unstable isotopes (radioisotopes), which undergo alpha, beta and gamma decay.
Limitations of Bohr’s atomic model
- Each shell has a specific energy level, and electrons cannot exist outside of these orbits. The closer the shell is to the nucleus, smaller the energy of that shell.
- For electron to move to another shell, it must absorb or release energy. The amount of energy observed or emitted is dependednt on the difference in energy between the shells.
- When an electron moves to a smaller shell, it releases energy which we observe as light.
- Bohrs model is actually a simplification, electrons do not actually move around nucleus of an atom in neat circular shells.
Heisenberg’s uncertainty principle?
Heisenberg and Schrodinger demonstrated we cannot know with certainty where an electron will be at any given time. We can however identify a 3 dimensional region where a particular electron can be found for 90% of the time. We call this region, an orbital.
No. of electrons in M shell of element with atomic no. 17?
Electronic config. = 1s2 2s 2p6 3s2 3p5
M-shell is 3rd shell, i.e. n=3, so electron in 3rd shell = 2+5= 7.
2 e in 3s2 + 5 e in 3p5 = 7e in M shell (n=3)
Atomic trends/ properties
What are the trends for atomic radius of an element?
- Within each period, the trend in atomic radius decreases as atomic no. increases, i.e. atoms with more electrons have a smaller atomic radius.
- This can be explained with concept of effective nuclear charge, the pull extended on a specific e by the nucleus, taking into account any electron-electron repulsions.
- Outermost electrons are easiest to remove- they have the highest energies, are shielded more, and are furthest from the nucleus.
What is ionisation energy?
Amount of energy required to remove the most loosely bound electron in its ground state is called its 1st ionisation energy.
X(g) –> X+ + e
Energy required to removed 2nd most loosely bound e is called 2nd ionisation energy and so on..
Energy is always required to remove e from atoms or ions, so ionization processes are always endothermic and ionization energy values are always positive.
Atomic trends/ properties
Trends for ionisation energy?
For larger atoms, the most loosely bound e is located farther from the nucleus and so is easier to remove. Therefore, as size (Atomic radius) increases, ionization energy should decrease.
1st ionization energy decreases down a group and increases across a period.
Atomic trends/ properties
Define Electronegativity, and how it is measured
Electronegativity of an atom is how strongly it attracts electrons towards itself. It depends on the atomic radius and atomic no. of the element.
Electronegativity is most commonly measured on the Pauling Scale. Values are shown relative to F, which has highest electronegativity.
Atomic trends/ properties
Define Melting Point
M.P. of an element is the temp at which solid to liquid phase change occurs.
Values shown relative to Carbon’s sublimation point, the highest temp at which any element remains solid.
Atomic trends/ properties
Boiling Point
B.P of an element is the temp at which liquid to gas change occurs.
Values shown relative to Rhenium (Re), element with highest B.P.
Atomic trends/ properties
Density
Amount of mass per unit volume, normally measued in g/cm^3 at room temp.
Values given relative to osmium (Os), element with highest density.
