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/cm3.

Gallium is a soft metal with a melting point of 29.7°C and a density of

5.91 g/cm3.

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).

periodic lawthe pattern of repeating properties

displayed by elements in the periodic table

Groups are verticaland have similar properties

Group 1 = H through Fr

Periods are horizontalPeriod 2 = Li through Ne

Elements are classified as metals, nonmetals,

and metalloids

Metals 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.

Nonmetals 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 s1 electrons and are extremely reactive(Group 2-alkaline earth metals, Group17-Halogens, p.162)

Group18 noble gases. Helium s2

all others are stables2p6

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 178

• Ions with positive charges are smaller than atoms (lost electrons)

• Ions with negative charges are larger than atoms (gained electrons)