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2.5 The Structure of the Atom -- Part 1
The size of an atom is the same for all elements.
In his time, scientists discovered about 65 different elements, and chemists identified many of their physical and chemical properties.
There was no systematic way of organizing them.
When he listed elements in order of increasing mass, they recurred in a periodic pattern.
The elements are arranged in a way that increases their mass.
To be periodic is to show a repeating pattern.
The table consists of a series of rows in which mass increases from left to right.
The rows were arranged so that elements with the same properties fell in the same columns.
The elements are listed in order of their atomic number.
The Ca properties are the same color.
There are elements that have the same properties that recur in a regular pattern.
The existence of an element was predicted by Mendeleev.
He named it germanium after his home country.
Ca number is more important than relative mass.
The periodic law was based on observation.
The periodic law summarizes many observations, but it doesn't give a reason for the observations in a table with atomic number ing.
In Chapters 8 and 9 we will look at a powerful theory that explains the law and gives the underlying reasons for it.
Gold, copper, strontium, and lead are some of the typical metals.
The zigzag diagonal line is the dividing line between metals and nonmetals.
Nonmetals have a variety of properties, but typically they are poor conductors of heat and electricity and gain electrons when they undergo chemical changes.
Sulfur, bromine, and iodine are nonmetals.
Several metalloids are honored on a Soviet postage stamp.
Semiconductors are useful to us in the manufacture of electronic chips because of their ability to change and control the conductivity.
There are some good examples of metalloids.
There are columns labeled with a number and a letter.
The numbers 1-18 are used in an alternative numbering system.
Most of the periodic tables in this book show both numbering systems.
The elements in a group have the same properties.
Na is used to fill balloons.
Helium is safe to put into balloons because it does not combine with other elements to form compounds.
When dropped into water, a marble-sized piece of sodium explodes.
Rb rubidium is an alkali metal.
Cs don't explode as much as sodium.
Magnesium, strontium, and barium are alkaline earth metals.
A group or family is one of the eight columns.
The periodic table can be used to predict the properties of main-group elements.
Transition elements in the middle of the table are less predictable.
Chlorine is a greenish-yellow gas with a strong odor.
Chlorine is used as a sterilizing agent.
bromine, a red-brown liquid that can easily evaporate into a gas, is one of the halogens.
In chemical reactions, metals tend to lose electrons and nonmetals tend to gain them.
The charge of the resulting ion can be predictable by the number of electrons lost or gained.
The main-group elements have the same number of electrons as the nearest noble gas.
I 1+ cation has the same number of electrons as helium.
A 1- anion formed by chlorine and argon has the same number of electrons.
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