Questions

An isotope is an atom where the number of neutrons is different to the number of protons.

The atomic mass or weight is an average weight of all the different isotopes that appear in nature for an element.

When an atom gives away one or more electrons it is said to be an ion.

Each row represents a period. This is the number of electron shells the atom has.

Each column represents a group. The outermost shell is called the valence. Each shell can have a maximum number of electrons. The first shell can have up to 2 electrons. Then 8, then. The groups represent the number of valence electrons.

The radius tends to get smaller as you go from left to right. This is because their are more protons in the centre which pull harder on the electrons thus contracting the radius.

Ionization energy is the energy required to remove an electron from the atom. Less is required on larger atoms because the attactive force drops off with distance and the shells of larger atoms is further from the nucleus. It’s the opposite of atomic radius. It’s very difficult to ionize helium because it only has one shell that’s close to its nucleus and that shell is full. There are multiple ionization energies for each electron removed from the atom. The second and subsequent ionization energies is always greater than the first and previous energies.

Electron affinity tells us how much an atom wants to gain an electron. Fluorine has the highest electron affinity because its outer shell needs one electron in it’s outer, and only second shell. On the other end (left side) the elements have only one electron in their outer shell and want to lose them. The trend is from bottom left to top right (ignoring the noble gases).

Electronegativity is the ability of an atom to hold electrons tightly. The trend is the same as electron affinity, bottom left to top right but ignoring the noble gases. Electronegativity is important for chemical bonds.

radioactive

4 types:

1. alpha particles - 2 protons and 2 neutrons (same as a helium nucleus). These can travel about 5cm in air before they collide with air particles and stop. Can be stopped by a piece of paper. Very strongly ionising.
2. beta particles - electrons ejected from the nucleus at very high speed. These are formed inside the nucleus when a neutron changes into a proton and an electron. These can travel around 15cm in air before stopping. Can be stopped by several mm of aluminium. Quite strongly ionising.
3. gamma rays - electromagnetic radiation from the nucleus. These travel several metres in air before stopping. Stopped by several cm of 1ead. Weakly ionising.
4. neutron -

ionising power is the power of radiation to colliding with atoms and causing them to lose electrons and become ions.

Some isotopes have an unstable nucleus. To become stable the nucleus gives out radiation. This is called radioactive decay. This is a completely random process.

Activity is the rate at which a source of unstable nuclei decay, This is measured in becquerel or bq. 1bq = 1 decay per second.

Heavenly bodies

In ancient times the 7 known metals were associated with the 7 known heavenly bodies: