In a video store, the latest movies are usually placed on the shelves in alphabetical order. Older movies are grouped into categories such as Action or Comedy. The manager has to choose a set of categories and then place each movie in the most appropriate location.

Scientists faced a similar challenge when they looked for a logical way to organize the elements.

Mendeleev arranged the elements into rows in order of increasing mass (not atomic #) so that elements with similar properties were in the same column.

There was a hole in this table… a missing element that had not been discovered at the time. Mendeleev predicted the properties of a missing element in his table. He said that eka- aluminum would be a soft metal with a low melting point and a density of 5.9 g/cm 3.

Gallium is a soft metal with a melting point of 29.7°C and a density of 5.91 g/cm 3.

The close match between Mendeleev's predictions and the actual properties of new elements showed how useful his periodic table could be.

In the modern periodic table, elements are arranged by increasing atomic number (number of protons).

periodicperiodic law the pattern of repeating properties displayed by elements in the periodic table

Groups are vertical and have similar properties Group 1 = H through Fr Periods are horizontal Period 2 = Li through Ne

Elements are classified as metals, nonmetals, and metalloids

MetalsMetals are elements that are good conductors of electric current and heat. Most metals are malleable, they do not shatter when hit. Many metals are ductile; that is, they can be drawn into thin wires.

NonmetalsNonmetals are elements that are poor conductors of heat and electric current. All the gases in the periodic table are nonmetals. The nonmetals that are solids at room temperature tend to be brittle. If they are hit with a hammer, they shatter or crumble.

Metalloids are elements with properties that fall between those of metals and nonmetals. For example, metals are good conductors of electric current and nonmetals are poor conductors of electric current.

The elements in Group 1 are called alkali metals. These metals have s 1 electrons and are extremely reactive (Group 2-alkaline earth metals, Group17-Halogens, p.162)metals

Group18 noble gases. Helium s 2 all others are stable s 2 p 6

s, p, d, f blocks

Electronegativity – how much the nucleus wants the electron Atomic radii decreases as electronegativity increases.

Ions- have lost or gained electrons Would something with a high electronegativity want to lose or gain electrons?

Sketch a table, and leave some space

Periodic Trends

First ionization energy – energy needed to remove 1 electron

Which would take more energy to remove an electron from? Fluorine or Oxygen

Electrons have a negative charge How does the charge of an atom change if the atom gains an electron? How does the charge of an atom change if the atom loses an electron?

Atom vs Common Ion Radii p 178Ion

Ions with positive charges are smaller than atoms (lost electrons) Ions with negative charges are larger than atoms (gained electrons)