This applet shows the periodicity of some physical and chemical properties of the elements.

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Generally as we move left to right across a period, atomic radius decreases, ionization energy increases, electronegativity increases.
Atomic radius usually decreases because each successive element has an added proton and electron which causes the electron to be drawn closer to the nucleus.
Ionization energy increases because the more tightly bound an element is, the more energy is required to remove an electron.
Electronegativity increases in the same manner as ionization energy because of the pull exerted on the electrons by the nucleus.
Boiling points and melting points increase and then decrease as we move left to right across a period.

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